Produce helpful diagnostics when converting to a facet fails (#5109)

When converting to a facet there are three different failure modes:

1. You provided a non-type value. Only types can convert to facets. So
we tell you that we found a non-type value.
2. You provided a facet type (which has type TypeType) which does not
have witnesses for the the target facet's type. So we tell you that the
type `T` implements `X` but needs to implement `Y`.
2. You provided a (non-facet-type) concrete type (of type TypeType)
which does not implement the target facet's type (which is a FacetType).
So we tell you that we need the type to implement the FacetType but it
does not.
3. You provided a FacetAccessType (which is of type TypeType also, but
we special case this), whose underlying FacetType is not compatible with
the target facet's type. So we tell you that we need the type to
implement `X` but found a FacetAccessType `T` which implements `Y`.

Closes #5027

toolchain/check/convert.cpp

@@ -1123,6 +1123,59 @@ static auto PerformCopy(Context& context, SemIR::InstId expr_id, bool diagnose)
   return SemIR::ErrorInst::SingletonInstId;
 }
 
+static auto DiagnoseConversionFailureToConstraintValue(Context& context,
+                                                       SemIR::LocId loc_id,
+                                                       SemIR::InstId expr_id,
+                                                       ConversionTarget target)
+    -> DiagnosticBuilder {
+  CARBON_DCHECK(target.type_id == SemIR::TypeType::SingletonTypeId ||
+                context.types().Is<SemIR::FacetType>(target.type_id));
+
+  auto type_of_expr_id = context.insts().Get(expr_id).type_id();
+  if (context.types().IsFacetType(type_of_expr_id)) {
+    // If the source type is/has a facet value, then we can include its
+    // FacetType in the diagnostic to help explain what interfaces the
+    // source type implements.
+    auto facet_value_inst_id = SemIR::InstId::None;
+    if (auto facet_access_type =
+            context.insts().TryGetAs<SemIR::FacetAccessType>(expr_id)) {
+      facet_value_inst_id = facet_access_type->facet_value_inst_id;
+    } else if (context.types().Is<SemIR::FacetType>(type_of_expr_id)) {
+      facet_value_inst_id = expr_id;
+    }
+
+    if (facet_value_inst_id.has_value()) {
+      CARBON_DIAGNOSTIC(
+          ConversionFailureFacetToFacet, Error,
+          "cannot{0:| implicitly} convert type {1} that implements {2} "
+          "into type implementing {3}{0: with `as`|}",
+          BoolAsSelect, InstIdAsType, TypeOfInstId, SemIR::TypeId);
+      return context.emitter().Build(
+          loc_id, ConversionFailureFacetToFacet,
+          target.kind == ConversionTarget::ExplicitAs, expr_id,
+          facet_value_inst_id, target.type_id);
+    } else {
+      CARBON_DIAGNOSTIC(ConversionFailureTypeToFacet, Error,
+                        "cannot{0:| implicitly} convert type {1} "
+                        "into type implementing {2}{0: with `as`|}",
+                        BoolAsSelect, InstIdAsType, SemIR::TypeId);
+      return context.emitter().Build(
+          loc_id, ConversionFailureTypeToFacet,
+          target.kind == ConversionTarget::ExplicitAs, expr_id, target.type_id);
+    }
+  } else {
+    CARBON_DIAGNOSTIC(
+        ConversionFailureNonTypeToFacet, Error,
+        "cannot{0:| implicitly} convert non-type value of type {1} "
+        "{2:to|into type implementing} {3}{0: with `as`|}",
+        BoolAsSelect, TypeOfInstId, BoolAsSelect, SemIR::TypeId);
+    return context.emitter().Build(
+        loc_id, ConversionFailureNonTypeToFacet,
+        target.kind == ConversionTarget::ExplicitAs, expr_id,
+        target.type_id == SemIR::TypeType::SingletonTypeId, target.type_id);
+  }
+}
+
 auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
              ConversionTarget target) -> SemIR::InstId {
   auto& sem_ir = context.sem_ir();
@@ -1208,19 +1261,24 @@ auto Convert(Context& context, SemIR::LocId loc_id, SemIR::InstId expr_id,
       if (!target.diagnose) {
         return context.emitter().BuildSuppressed();
       }
-      // TODO: Should this message change to say "object of type" when
-      // converting from a reference expression?
-      CARBON_DIAGNOSTIC(ImplicitAsConversionFailure, Error,
-                        "cannot implicitly convert value of type {0} to {1}",
-                        TypeOfInstId, SemIR::TypeId);
-      CARBON_DIAGNOSTIC(ExplicitAsConversionFailure, Error,
-                        "cannot convert value of type {0} to {1} with `as`",
-                        TypeOfInstId, SemIR::TypeId);
-      return context.emitter().Build(loc_id,
-                                     target.kind == ConversionTarget::ExplicitAs
-                                         ? ExplicitAsConversionFailure
-                                         : ImplicitAsConversionFailure,
-                                     expr_id, target.type_id);
+      if (target.type_id == SemIR::TypeType::SingletonTypeId ||
+          sem_ir.types().Is<SemIR::FacetType>(target.type_id)) {
+        // TODO: Move this to PerformBuiltinConversion(). See
+        // https://github.com/carbon-language/carbon-lang/issues/5122.
+        return DiagnoseConversionFailureToConstraintValue(context, loc_id,
+                                                          expr_id, target);
+      } else {
+        // TODO: Should this message change to say "object of type" when
+        // converting from a reference expression?
+        CARBON_DIAGNOSTIC(ConversionFailure, Error,
+                          "cannot{0:| implicitly} convert value of type {1} to "
+                          "{2}{0: with `as`|}",
+                          BoolAsSelect, TypeOfInstId, SemIR::TypeId);
+        return context.emitter().Build(
+            loc_id, ConversionFailure,
+            target.kind == ConversionTarget::ExplicitAs, expr_id,
+            target.type_id);
+      }
     });
 
     // Pull a value directly out of the initializer if possible and wanted.

toolchain/check/testdata/array/fail_bound_overflow.carbon

@@ -14,7 +14,7 @@
 // CHECK:STDERR:
 var a: array(i32, 39999999999999999993);
 
-// CHECK:STDERR: fail_bound_overflow.carbon:[[@LINE+7]]:14: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_bound_overflow.carbon:[[@LINE+7]]:14: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: var b: array(1, 39999999999999999993);
 // CHECK:STDERR:              ^
 // CHECK:STDERR: fail_bound_overflow.carbon:[[@LINE+4]]:14: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/array/fail_invalid_type.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/array/fail_invalid_type.carbon
 
-// CHECK:STDERR: fail_invalid_type.carbon:[[@LINE+7]]:14: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_invalid_type.carbon:[[@LINE+7]]:14: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: var a: array(1, 1);
 // CHECK:STDERR:              ^
 // CHECK:STDERR: fail_invalid_type.carbon:[[@LINE+4]]:14: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/array/fail_type_mismatch.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/array/fail_type_mismatch.carbon
 
-// CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:24: error: cannot implicitly convert value of type `String` to `i32` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:24: error: cannot implicitly convert value of type `String` to `i32` [ConversionFailure]
 // CHECK:STDERR: var a: array(i32, 3) = (1, "Hello", "World");
 // CHECK:STDERR:                        ^~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+4]]:24: note: type `String` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]
@@ -18,7 +18,7 @@
 var a: array(i32, 3) = (1, "Hello", "World");
 
 var t1: (i32, String, String);
-// CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:24: error: cannot implicitly convert value of type `String` to `i32` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:24: error: cannot implicitly convert value of type `String` to `i32` [ConversionFailure]
 // CHECK:STDERR: var b: array(i32, 3) = t1;
 // CHECK:STDERR:                        ^~
 // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+4]]:24: note: type `String` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/as/adapter_conversion.carbon

@@ -154,7 +154,7 @@ class B {
 // We do not try to implicitly convert from the first operand of `as` to the
 // adapted type of the second operand.
 
-// CHECK:STDERR: fail_adapt_init_from_struct.carbon:[[@LINE+7]]:12: error: cannot convert value of type `{.x: Core.IntLiteral}` to `B` with `as` [ExplicitAsConversionFailure]
+// CHECK:STDERR: fail_adapt_init_from_struct.carbon:[[@LINE+7]]:12: error: cannot convert value of type `{.x: Core.IntLiteral}` to `B` with `as` [ConversionFailure]
 // CHECK:STDERR: var b: B = {.x = 1} as B;
 // CHECK:STDERR:            ^~~~~~~~~~~~~
 // CHECK:STDERR: fail_adapt_init_from_struct.carbon:[[@LINE+4]]:12: note: type `{.x: Core.IntLiteral}` does not implement interface `Core.As(B)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/as/fail_no_conversion.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/as/fail_no_conversion.carbon
 
-// CHECK:STDERR: fail_no_conversion.carbon:[[@LINE+7]]:21: error: cannot convert value of type `Core.IntLiteral` to `(i32, i32)` with `as` [ExplicitAsConversionFailure]
+// CHECK:STDERR: fail_no_conversion.carbon:[[@LINE+7]]:21: error: cannot convert value of type `Core.IntLiteral` to `(i32, i32)` with `as` [ConversionFailure]
 // CHECK:STDERR: let n: (i32, i32) = 1 as (i32, i32);
 // CHECK:STDERR:                     ^~~~~~~~~~~~~~~
 // CHECK:STDERR: fail_no_conversion.carbon:[[@LINE+4]]:21: note: type `Core.IntLiteral` does not implement interface `Core.As((i32, i32))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/as/fail_not_type.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/as/fail_not_type.carbon
 
-// CHECK:STDERR: fail_not_type.carbon:[[@LINE+7]]:19: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_not_type.carbon:[[@LINE+7]]:19: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: let n: i32 = 1 as 2;
 // CHECK:STDERR:                   ^
 // CHECK:STDERR: fail_not_type.carbon:[[@LINE+4]]:19: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/basics/fail_non_type_as_type.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/basics/fail_non_type_as_type.carbon
 
-// CHECK:STDERR: fail_non_type_as_type.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_non_type_as_type.carbon:[[@LINE+7]]:1: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: var x: type = 42;
 // CHECK:STDERR: ^~~~~~~~~~~
 // CHECK:STDERR: fail_non_type_as_type.carbon:[[@LINE+4]]:1: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/builtin_conversions/no_prelude/convert_class_value_to_generic_facet_value_value.carbon

@@ -72,7 +72,7 @@ impl forall [T:! type] C as I(T, ()) {}
 fn A[T:! I({}, {})](t: T) {}
 
 fn B() {
-  // CHECK:STDERR: fail_mismatch_impl_constraint_with_fixed_specific.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `I({}, {})` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_mismatch_impl_constraint_with_fixed_specific.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `C` into type implementing `I({}, {})` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   A({} as C);
   // CHECK:STDERR:   ^~~~~~~~~~
   // CHECK:STDERR: fail_mismatch_impl_constraint_with_fixed_specific.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(I({}, {}))` [MissingImplInMemberAccessNote]
@@ -99,7 +99,7 @@ impl forall [T:! type] C(T, ()) as I {}
 fn A[T:! I](t: T) {}
 
 fn B() {
-  // CHECK:STDERR: fail_mismatch_impl_self_with_fixed_specific.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `I` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_mismatch_impl_self_with_fixed_specific.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `C({}, {})` into type implementing `I` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   A({} as C({}, {}));
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_mismatch_impl_self_with_fixed_specific.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(I)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/builtin_conversions/no_prelude/fail_convert_class_type_to_generic_facet_value.carbon

@@ -35,7 +35,7 @@ impl ImplsGeneric as Generic(GenericParam) {
 fn CallGenericMethod(T:! type, U:! Generic(T)) {}
 
 fn G() {
-  // CHECK:STDERR: fail_convert_class_type_to_generic_facet_value.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `Generic(WrongGenericParam)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_convert_class_type_to_generic_facet_value.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `ImplsGeneric` into type implementing `Generic(WrongGenericParam)` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   CallGenericMethod(WrongGenericParam, ImplsGeneric);
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_convert_class_type_to_generic_facet_value.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(Generic(WrongGenericParam))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/builtin_conversions/no_prelude/fail_convert_facet_value_shouldnt_know_concrete_type.carbon

@@ -36,7 +36,7 @@ impl Goat as Eats {}
 fn Feed(e:! Eats) {}
 
 fn F() {
-  // CHECK:STDERR: fail_convert_facet_value_shouldnt_know_concrete_type.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `Animal` to `Eats` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_convert_facet_value_shouldnt_know_concrete_type.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `Goat as Animal` that implements `Animal` into type implementing `Eats` [ConversionFailureFacetToFacet]
   // CHECK:STDERR:   Feed(Goat as Animal);
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_convert_facet_value_shouldnt_know_concrete_type.carbon:[[@LINE+7]]:3: note: type `Animal` does not implement interface `Core.ImplicitAs(Eats)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/builtin_conversions/no_prelude/fail_convert_facet_value_to_missing_impl.carbon

@@ -27,7 +27,7 @@ interface Animal {}
 
 fn Feed[T:! Eats](e: T) {}
 
-// CHECK:STDERR: fail_convert_facet_value_to_missing_impl.carbon:[[@LINE+10]]:37: error: cannot implicitly convert value of type `type` to `Eats` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_convert_facet_value_to_missing_impl.carbon:[[@LINE+10]]:37: error: cannot implicitly convert type `T` that implements `Animal` into type implementing `Eats` [ConversionFailureFacetToFacet]
 // CHECK:STDERR: fn HandleAnimal[T:! Animal](a: T) { Feed(a); }
 // CHECK:STDERR:                                     ^~~~~~~
 // CHECK:STDERR: fail_convert_facet_value_to_missing_impl.carbon:[[@LINE+7]]:37: note: type `type` does not implement interface `Core.ImplicitAs(Eats)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/builtin_conversions/no_prelude/fail_convert_type_erased_type_to_facet.carbon

@@ -35,7 +35,7 @@ fn WalkAnimal(a:! Animal) {}
 
 fn F() {
   let x:! type = Goat;
-  // CHECK:STDERR: fail_convert_type_erased_type_to_facet.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `Animal` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_convert_type_erased_type_to_facet.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `x` into type implementing `Animal` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   WalkAnimal(x);
   // CHECK:STDERR:   ^~~~~~~~~~~~~
   // CHECK:STDERR: fail_convert_type_erased_type_to_facet.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(Animal)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/builtins/int/convert.carbon

@@ -47,7 +47,7 @@ import library "int_ops";
 
 fn F() {
   // Ensure our testing machinery works.
-  // CHECK:STDERR: fail_self_test.carbon:[[@LINE+7]]:3: error: cannot convert value of type `Expect(0)` to `Expect(1)` with `as` [ExplicitAsConversionFailure]
+  // CHECK:STDERR: fail_self_test.carbon:[[@LINE+7]]:3: error: cannot convert value of type `Expect(0)` to `Expect(1)` with `as` [ConversionFailure]
   // CHECK:STDERR:   Test(Int32ToInt32(0)) as Expect(1 as i32);
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_self_test.carbon:[[@LINE+4]]:3: note: type `Expect(0)` does not implement interface `Core.As(Expect(1))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/adapter/extend_adapt.carbon

@@ -48,7 +48,7 @@ class SomeClassAdapter {
 }
 
 fn F(a: SomeClassAdapter) {
-  // CHECK:STDERR: fail_todo_method_access.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `SomeClassAdapter` to `SomeClass` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_method_access.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `SomeClassAdapter` to `SomeClass` [ConversionFailure]
   // CHECK:STDERR:   a.F();
   // CHECK:STDERR:   ^
   // CHECK:STDERR: fail_todo_method_access.carbon:[[@LINE+7]]:3: note: type `SomeClassAdapter` does not implement interface `Core.ImplicitAs(SomeClass)` [MissingImplInMemberAccessNote]
@@ -75,7 +75,7 @@ class SomeClassAdapter {
 }
 
 fn F(a: SomeClassAdapter) -> i32 {
-  // CHECK:STDERR: fail_todo_field_access.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `SomeClassAdapter` to `SomeClass` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_field_access.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `SomeClassAdapter` to `SomeClass` [ConversionFailure]
   // CHECK:STDERR:   return a.b;
   // CHECK:STDERR:          ^~~
   // CHECK:STDERR: fail_todo_field_access.carbon:[[@LINE+4]]:10: note: type `SomeClassAdapter` does not implement interface `Core.ImplicitAs(SomeClass)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/adapter/fail_adapt_bad_decl.carbon

@@ -13,7 +13,7 @@
 library "[[@TEST_NAME]]";
 
 class Bad {
-  // CHECK:STDERR: fail_not_type.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_not_type.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   adapt 100;
   // CHECK:STDERR:   ^~~~~~~~~~
   // CHECK:STDERR: fail_not_type.carbon:[[@LINE+4]]:3: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]
@@ -34,7 +34,7 @@ fn Use(b: Bad) { b.F(); }
 library "[[@TEST_NAME]]";
 
 class Bad {
-  // CHECK:STDERR: fail_extend_not_type.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_extend_not_type.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   extend adapt 100;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_extend_not_type.carbon:[[@LINE+4]]:3: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/adapter/init_adapt.carbon

@@ -52,7 +52,7 @@ let a: C = {.a = 1, .b = 2};
 
 // Cannot implicitly convert between a type and an adapter for the type.
 
-// CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+7]]:17: error: cannot implicitly convert value of type `C` to `AdaptC` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+7]]:17: error: cannot implicitly convert value of type `C` to `AdaptC` [ConversionFailure]
 // CHECK:STDERR: let b: AdaptC = a;
 // CHECK:STDERR:                 ^
 // CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+4]]:17: note: type `C` does not implement interface `Core.ImplicitAs(AdaptC)` [MissingImplInMemberAccessNote]
@@ -61,7 +61,7 @@ let a: C = {.a = 1, .b = 2};
 // CHECK:STDERR:
 let b: AdaptC = a;
 
-// CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+7]]:12: error: cannot implicitly convert value of type `AdaptC` to `C` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+7]]:12: error: cannot implicitly convert value of type `AdaptC` to `C` [ConversionFailure]
 // CHECK:STDERR: let c: C = b;
 // CHECK:STDERR:            ^
 // CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+4]]:12: note: type `AdaptC` does not implement interface `Core.ImplicitAs(C)` [MissingImplInMemberAccessNote]
@@ -74,7 +74,7 @@ fn MakeC() -> C;
 
 fn MakeAdaptC() -> AdaptC;
 
-// CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `C` to `AdaptC` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `C` to `AdaptC` [ConversionFailure]
 // CHECK:STDERR: var d: AdaptC = MakeC();
 // CHECK:STDERR: ^~~~~~~~~~~~~
 // CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+4]]:1: note: type `C` does not implement interface `Core.ImplicitAs(AdaptC)` [MissingImplInMemberAccessNote]
@@ -83,7 +83,7 @@ fn MakeAdaptC() -> AdaptC;
 // CHECK:STDERR:
 var d: AdaptC = MakeC();
 
-// CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `AdaptC` to `C` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `AdaptC` to `C` [ConversionFailure]
 // CHECK:STDERR: var e: C = MakeAdaptC();
 // CHECK:STDERR: ^~~~~~~~
 // CHECK:STDERR: fail_not_implicit.carbon:[[@LINE+4]]:1: note: type `AdaptC` does not implement interface `Core.ImplicitAs(C)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/fail_base_bad_type.carbon

@@ -28,7 +28,7 @@ fn AccessMemberWithInvalidBaseError(p: DeriveFromError*) -> i32 { return (*p).n;
 library "[[@TEST_NAME]]";
 
 class DeriveFromNonType {
-  // CHECK:STDERR: fail_derive_from_non_type.carbon:[[@LINE+7]]:16: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_derive_from_non_type.carbon:[[@LINE+7]]:16: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   extend base: 32;
   // CHECK:STDERR:                ^~
   // CHECK:STDERR: fail_derive_from_non_type.carbon:[[@LINE+4]]:16: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]
@@ -76,7 +76,7 @@ class DeriveFromTuple {
   extend base: (Base,);
 }
 
-// CHECK:STDERR: fail_derive_from_tuple.carbon:[[@LINE+7]]:61: error: cannot implicitly convert value of type `DeriveFromTuple*` to `(Base,)*` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_derive_from_tuple.carbon:[[@LINE+7]]:61: error: cannot implicitly convert value of type `DeriveFromTuple*` to `(Base,)*` [ConversionFailure]
 // CHECK:STDERR: fn ConvertToBadBaseTuple(p: DeriveFromTuple*) -> (Base,)* { return p; }
 // CHECK:STDERR:                                                             ^~~~~~~~~
 // CHECK:STDERR: fail_derive_from_tuple.carbon:[[@LINE+4]]:61: note: type `DeriveFromTuple*` does not implement interface `Core.ImplicitAs((Base,)*)` [MissingImplInMemberAccessNote]
@@ -101,7 +101,7 @@ class DeriveFromStruct {
   extend base: {.a: i32, .b: i32};
 }
 
-// CHECK:STDERR: fail_derive_from_struct.carbon:[[@LINE+7]]:74: error: cannot implicitly convert value of type `DeriveFromStruct*` to `{.a: i32, .b: i32}*` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_derive_from_struct.carbon:[[@LINE+7]]:74: error: cannot implicitly convert value of type `DeriveFromStruct*` to `{.a: i32, .b: i32}*` [ConversionFailure]
 // CHECK:STDERR: fn ConvertToBadBaseStruct(p: DeriveFromStruct*) -> {.a: i32, .b: i32}* { return p; }
 // CHECK:STDERR:                                                                          ^~~~~~~~~
 // CHECK:STDERR: fail_derive_from_struct.carbon:[[@LINE+4]]:74: note: type `DeriveFromStruct*` does not implement interface `Core.ImplicitAs({.a: i32, .b: i32}*)` [MissingImplInMemberAccessNote]
@@ -134,7 +134,7 @@ class DeriveFromIncomplete {
   extend base: Incomplete;
 }
 
-// CHECK:STDERR: fail_derive_from_incomplete.carbon:[[@LINE+7]]:74: error: cannot implicitly convert value of type `DeriveFromIncomplete*` to `Incomplete*` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_derive_from_incomplete.carbon:[[@LINE+7]]:74: error: cannot implicitly convert value of type `DeriveFromIncomplete*` to `Incomplete*` [ConversionFailure]
 // CHECK:STDERR: fn ConvertToBadBaseIncomplete(p: DeriveFromIncomplete*) -> Incomplete* { return p; }
 // CHECK:STDERR:                                                                          ^~~~~~~~~
 // CHECK:STDERR: fail_derive_from_incomplete.carbon:[[@LINE+4]]:74: note: type `DeriveFromIncomplete*` does not implement interface `Core.ImplicitAs(Incomplete*)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/fail_compound_type_mismatch.carbon

@@ -17,7 +17,7 @@ class B {
 }
 
 fn AccessBInA(a: A) -> i32 {
-  // CHECK:STDERR: fail_compound_type_mismatch.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `A` to `B` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_compound_type_mismatch.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `A` to `B` [ConversionFailure]
   // CHECK:STDERR:   return a.(B.b);
   // CHECK:STDERR:          ^~~~~~~
   // CHECK:STDERR: fail_compound_type_mismatch.carbon:[[@LINE+4]]:10: note: type `A` does not implement interface `Core.ImplicitAs(B)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/fail_derived_to_base.carbon

@@ -21,7 +21,7 @@ class B2 {
   var b: i32;
 }
 
-// CHECK:STDERR: fail_derived_to_base.carbon:[[@LINE+7]]:38: error: cannot implicitly convert value of type `B2*` to `A1*` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_derived_to_base.carbon:[[@LINE+7]]:38: error: cannot implicitly convert value of type `B2*` to `A1*` [ConversionFailure]
 // CHECK:STDERR: fn ConvertUnrelated(p: B2*) -> A1* { return p; }
 // CHECK:STDERR:                                      ^~~~~~~~~
 // CHECK:STDERR: fail_derived_to_base.carbon:[[@LINE+4]]:38: note: type `B2*` does not implement interface `Core.ImplicitAs(A1*)` [MissingImplInMemberAccessNote]
@@ -32,7 +32,7 @@ fn ConvertUnrelated(p: B2*) -> A1* { return p; }
 
 class Incomplete;
 
-// CHECK:STDERR: fail_derived_to_base.carbon:[[@LINE+7]]:47: error: cannot implicitly convert value of type `Incomplete*` to `A2*` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_derived_to_base.carbon:[[@LINE+7]]:47: error: cannot implicitly convert value of type `Incomplete*` to `A2*` [ConversionFailure]
 // CHECK:STDERR: fn ConvertIncomplete(p: Incomplete*) -> A2* { return p; }
 // CHECK:STDERR:                                               ^~~~~~~~~
 // CHECK:STDERR: fail_derived_to_base.carbon:[[@LINE+4]]:47: note: type `Incomplete*` does not implement interface `Core.ImplicitAs(A2*)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/fail_self.carbon

@@ -43,7 +43,7 @@ class WrongSelf {
 }
 
 fn CallWrongSelf(ws: WrongSelf) {
-  // CHECK:STDERR: fail_self.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `WrongSelf` to `Class` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_self.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `WrongSelf` to `Class` [ConversionFailure]
   // CHECK:STDERR:   ws.F();
   // CHECK:STDERR:   ^~
   // CHECK:STDERR: fail_self.carbon:[[@LINE+7]]:3: note: type `WrongSelf` does not implement interface `Core.ImplicitAs(Class)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/generic/adapt.carbon

@@ -48,7 +48,7 @@ class Adapter {
 
 fn Access(a: Adapter) -> i32 {
   // TODO: This should presumably work, but the design doesn't say how yet.
-  // CHECK:STDERR: fail_todo_extend_adapt_specific_type.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `Adapter` to `C(i32)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_extend_adapt_specific_type.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `Adapter` to `C(i32)` [ConversionFailure]
   // CHECK:STDERR:   return a.x;
   // CHECK:STDERR:          ^~~
   // CHECK:STDERR: fail_todo_extend_adapt_specific_type.carbon:[[@LINE+4]]:10: note: type `Adapter` does not implement interface `Core.ImplicitAs(C(i32))` [MissingImplInMemberAccessNote]
@@ -81,7 +81,7 @@ import library "extend_adapt_specific_type_library";
 
 fn ImportedAccess(a: Adapter) -> i32 {
   // TODO: This should presumably work, but the design doesn't say how yet.
-  // CHECK:STDERR: fail_todo_import_extend_adapt_specific_type.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `Adapter` to `C(i32)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_import_extend_adapt_specific_type.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `Adapter` to `C(i32)` [ConversionFailure]
   // CHECK:STDERR:   return a.x;
   // CHECK:STDERR:          ^~~
   // CHECK:STDERR: fail_todo_import_extend_adapt_specific_type.carbon:[[@LINE+4]]:10: note: type `Adapter` does not implement interface `Core.ImplicitAs(C(i32))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/generic/call.carbon

@@ -55,7 +55,7 @@ library "[[@TEST_NAME]]";
 
 class Class(T:! type, N:! i32) {}
 
-// CHECK:STDERR: fail_no_conversion.carbon:[[@LINE+10]]:8: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_no_conversion.carbon:[[@LINE+10]]:8: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: var a: Class(5, i32*);
 // CHECK:STDERR:        ^~~~~~~~~~~~~~
 // CHECK:STDERR: fail_no_conversion.carbon:[[@LINE+7]]:8: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/generic/import.carbon

@@ -55,7 +55,7 @@ import library "foo";
 
 fn Use() {
   // TODO: Include the generic arguments in the formatted type name.
-  // CHECK:STDERR: fail_generic_arg_mismatch.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `CompleteClass(i32)` to `CompleteClass(i32*)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_generic_arg_mismatch.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `CompleteClass(i32)` to `CompleteClass(i32*)` [ConversionFailure]
   // CHECK:STDERR:   var v: CompleteClass(i32*) = F();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_generic_arg_mismatch.carbon:[[@LINE+4]]:3: note: type `CompleteClass(i32)` does not implement interface `Core.ImplicitAs(CompleteClass(i32*))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/generic/member_access.carbon

@@ -39,7 +39,7 @@ class Class(T:! type) {
 }
 
 fn StaticMemberFunctionCall(T:! type) -> Class(T) {
-  // CHECK:STDERR: fail_todo_static_member_fn_call.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `Class(T)` to `Class(T)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_static_member_fn_call.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `Class(T)` to `Class(T)` [ConversionFailure]
   // CHECK:STDERR:   return Class(T).Make();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_todo_static_member_fn_call.carbon:[[@LINE+4]]:3: note: type `Class(T)` does not implement interface `Core.ImplicitAs(Class(T))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/generic/stringify.carbon

@@ -16,7 +16,7 @@ class NoParams {}
 class EmptyParams() {}
 
 var v: NoParams;
-// CHECK:STDERR: fail_empty_params.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `NoParams` to `EmptyParams()` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_empty_params.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `NoParams` to `EmptyParams()` [ConversionFailure]
 // CHECK:STDERR: var w: EmptyParams() = v;
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR: fail_empty_params.carbon:[[@LINE+4]]:1: note: type `NoParams` does not implement interface `Core.ImplicitAs(EmptyParams())` [MissingImplInMemberAccessNote]
@@ -37,7 +37,7 @@ class Outer(T:! type) {
 var v: Outer({}*);
 
 // TODO: It would be nice to include the `Outer({}*).` prefix in the name of `Inner`.
-// CHECK:STDERR: fail_nested.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `Outer({}*)` to `Inner({.a: i32}*)` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_nested.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `Outer({}*)` to `Inner({.a: i32}*)` [ConversionFailure]
 // CHECK:STDERR: var w: Outer({}*).Inner({.a: i32}*) = v;
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR: fail_nested.carbon:[[@LINE+4]]:1: note: type `Outer({}*)` does not implement interface `Core.ImplicitAs(Inner({.a: i32}*))` [MissingImplInMemberAccessNote]
@@ -52,7 +52,7 @@ library "[[@TEST_NAME]]";
 
 class C(N:! i32) {}
 
-// CHECK:STDERR: fail_int_value.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `()` to `C(123)` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_int_value.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `()` to `C(123)` [ConversionFailure]
 // CHECK:STDERR: var v: C(123) = ();
 // CHECK:STDERR: ^~~~~~~~~~~~~
 // CHECK:STDERR: fail_int_value.carbon:[[@LINE+4]]:1: note: type `()` does not implement interface `Core.ImplicitAs(C(123))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/class/self.carbon

@@ -32,7 +32,7 @@ fn Class.G[addr self: Self*]() -> i32 {
 library "[[@TEST_NAME]]";
 
 class Class {
-  // CHECK:STDERR: fail_return_self_value.carbon:[[@LINE+7]]:25: error: cannot implicitly convert value of type `Class` to `type` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_return_self_value.carbon:[[@LINE+7]]:25: error: cannot implicitly convert non-type value of type `Class` to `type` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   fn F[self: Self]() -> self;
   // CHECK:STDERR:                         ^~~~
   // CHECK:STDERR: fail_return_self_value.carbon:[[@LINE+4]]:25: note: type `Class` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/const/fail_collapse.carbon

@@ -13,7 +13,7 @@
 // CHECK:STDERR:         ^~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
 fn G(p: const (const i32)**) -> i32** {
-  // CHECK:STDERR: fail_collapse.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `const i32**` to `i32**` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_collapse.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `const i32**` to `i32**` [ConversionFailure]
   // CHECK:STDERR:   return p;
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR: fail_collapse.carbon:[[@LINE+4]]:3: note: type `const i32**` does not implement interface `Core.ImplicitAs(i32**)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/deduce/array.carbon

@@ -58,7 +58,7 @@ fn F[T:! type](a: array(T, 2)) -> T { return a[0]; }
 fn G() -> C {
   // TODO: We succeed at deducing T here but fail to convert. Is this the right behavior?
   var a: array(C, 3) = ({}, {}, {});
-  // CHECK:STDERR: fail_bound_mismatch.carbon:[[@LINE+10]]:12: error: cannot implicitly convert value of type `[C; 3]` to `[C; 2]` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_bound_mismatch.carbon:[[@LINE+10]]:12: error: cannot implicitly convert value of type `[C; 3]` to `[C; 2]` [ConversionFailure]
   // CHECK:STDERR:   return F(a);
   // CHECK:STDERR:            ^
   // CHECK:STDERR: fail_bound_mismatch.carbon:[[@LINE+7]]:12: note: type `[C; 3]` does not implement interface `Core.ImplicitAs([C; 2])` [MissingImplInMemberAccessNote]
@@ -83,7 +83,7 @@ fn F[N:! Core.IntLiteral()](a: array(C, N)) -> i32 { return N; }
 fn G() -> i32 {
   // TODO: We succeed at deducing N here but fail to convert. Is this the right behavior?
   var a: array(D, 3) = ({}, {}, {});
-  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+10]]:12: error: cannot implicitly convert value of type `[D; 3]` to `[C; 3]` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+10]]:12: error: cannot implicitly convert value of type `[D; 3]` to `[C; 3]` [ConversionFailure]
   // CHECK:STDERR:   return F(a);
   // CHECK:STDERR:            ^
   // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:12: note: type `[D; 3]` does not implement interface `Core.ImplicitAs([C; 3])` [MissingImplInMemberAccessNote]

toolchain/check/testdata/facet/min_prelude/combine.carbon

@@ -99,7 +99,7 @@ impl C as B {}
 fn G[T:! A(P2) & B](t: T) {}
 
 fn F() {
-  // CHECK:STDERR: fail_wrong_generic_interface.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `A(P2) & B` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_wrong_generic_interface.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `C` into type implementing `A(P2) & B` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   G({} as C);
   // CHECK:STDERR:   ^~~~~~~~~~
   // CHECK:STDERR: fail_wrong_generic_interface.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(A(P2) & B)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/facet/min_prelude/fail_incomplete.carbon

@@ -19,7 +19,7 @@ fn G[T:! A](t: T) {}
 fn H[T:! A & B](t: T) {}
 
 fn F() {
-  // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+7]]:17: error: cannot convert value of type `type` to `A` with `as` [ExplicitAsConversionFailure]
+  // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+7]]:17: error: cannot convert type `C` into type implementing `A` with `as` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   ({} as C) as (C as A);
   // CHECK:STDERR:                 ^~~~~~
   // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+4]]:17: note: type `type` does not implement interface `Core.As(A)` [MissingImplInMemberAccessNote]
@@ -28,7 +28,7 @@ fn F() {
   // CHECK:STDERR:
   ({} as C) as (C as A);
 
-  // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+7]]:17: error: cannot convert value of type `type` to `A & B` with `as` [ExplicitAsConversionFailure]
+  // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+7]]:17: error: cannot convert type `C` into type implementing `A & B` with `as` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   ({} as C) as (C as (A & B));
   // CHECK:STDERR:                 ^~~~~~~~~~~~
   // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+4]]:17: note: type `type` does not implement interface `Core.As(A & B)` [MissingImplInMemberAccessNote]
@@ -37,7 +37,7 @@ fn F() {
   // CHECK:STDERR:
   ({} as C) as (C as (A & B));
 
-  // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `A` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `C` into type implementing `A` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   G({} as C);
   // CHECK:STDERR:   ^~~~~~~~~~
   // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(A)` [MissingImplInMemberAccessNote]
@@ -49,7 +49,7 @@ fn F() {
   // CHECK:STDERR:
   G({} as C);
 
-  // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `A & B` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `C` into type implementing `A & B` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   H({} as C);
   // CHECK:STDERR:   ^~~~~~~~~~
   // CHECK:STDERR: fail_incomplete.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(A & B)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/facet/min_prelude/fail_todo_call_combined_impl_witness.carbon

@@ -39,7 +39,7 @@ fn G[T:! A & Empty & B](t: T) {
   // TODO: Qualified lookup of `AA` and `BB` should also be possible here, using
   // the witnesses found in type deduction.
 
-  // CHECK:STDERR: fail_todo_call_combined_impl_witness.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `Empty & A & B` to `A` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_call_combined_impl_witness.carbon:[[@LINE+7]]:3: error: cannot implicitly convert type `T` that implements `Empty & A & B` into type implementing `A` [ConversionFailureFacetToFacet]
   // CHECK:STDERR:   T.(A.AA)();
   // CHECK:STDERR:   ^~~~~~~~
   // CHECK:STDERR: fail_todo_call_combined_impl_witness.carbon:[[@LINE+4]]:3: note: type `Empty & A & B` does not implement interface `Core.ImplicitAs(A)` [MissingImplInMemberAccessNote]
@@ -47,7 +47,7 @@ fn G[T:! A & Empty & B](t: T) {
   // CHECK:STDERR:   ^~~~~~~~
   // CHECK:STDERR:
   T.(A.AA)();
-  // CHECK:STDERR: fail_todo_call_combined_impl_witness.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `Empty & A & B` to `B` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_call_combined_impl_witness.carbon:[[@LINE+7]]:3: error: cannot implicitly convert type `T` that implements `Empty & A & B` into type implementing `B` [ConversionFailureFacetToFacet]
   // CHECK:STDERR:   T.(B.BB)();
   // CHECK:STDERR:   ^~~~~~~~
   // CHECK:STDERR: fail_todo_call_combined_impl_witness.carbon:[[@LINE+4]]:3: note: type `Empty & A & B` does not implement interface `Core.ImplicitAs(B)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/function/call/fail_param_type.carbon

@@ -11,7 +11,7 @@
 fn G(a: i32) {}
 
 fn F() {
-  // CHECK:STDERR: fail_param_type.carbon:[[@LINE+10]]:5: error: cannot implicitly convert value of type `f64` to `i32` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_param_type.carbon:[[@LINE+10]]:5: error: cannot implicitly convert value of type `f64` to `i32` [ConversionFailure]
   // CHECK:STDERR:   G(1.0);
   // CHECK:STDERR:     ^~~
   // CHECK:STDERR: fail_param_type.carbon:[[@LINE+7]]:5: note: type `f64` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/function/call/fail_return_type_mismatch.carbon

@@ -11,7 +11,7 @@
 fn Foo() -> f64 { return 1.0; }
 
 fn Run() {
-  // CHECK:STDERR: fail_return_type_mismatch.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `f64` to `i32` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_return_type_mismatch.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `f64` to `i32` [ConversionFailure]
   // CHECK:STDERR:   var x: i32 = Foo();
   // CHECK:STDERR:   ^~~~~~~~~~
   // CHECK:STDERR: fail_return_type_mismatch.carbon:[[@LINE+4]]:3: note: type `f64` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/impl/assoc_const_self.carbon

@@ -28,7 +28,7 @@ interface I {
   let V:! Self;
 }
 
-// CHECK:STDERR: fail_assoc_const_mismatch.carbon:[[@LINE+7]]:12: error: cannot implicitly convert value of type `Core.IntLiteral` to `{}` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_assoc_const_mismatch.carbon:[[@LINE+7]]:12: error: cannot implicitly convert value of type `Core.IntLiteral` to `{}` [ConversionFailure]
 // CHECK:STDERR: impl {} as I where .V = 0 {}
 // CHECK:STDERR:            ^~~~~~~~~~~~~~
 // CHECK:STDERR: fail_assoc_const_mismatch.carbon:[[@LINE+4]]:12: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs({})` [MissingImplInMemberAccessNote]
@@ -86,7 +86,7 @@ fn F(T:! I where {} impls Core.ImplicitAs(.Self) and .V = {});
 
 fn CallF() {
   // TODO: This call should eventually work.
-  // CHECK:STDERR: fail_todo_constrained_fn.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `{}` to `I where .(I.V) = {} and...` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_constrained_fn.carbon:[[@LINE+10]]:3: error: cannot implicitly convert non-type value of type `{}` into type implementing `I where .(I.V) = {} and...` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   F({});
   // CHECK:STDERR:   ^~~~~
   // CHECK:STDERR: fail_todo_constrained_fn.carbon:[[@LINE+7]]:3: note: type `{}` does not implement interface `Core.ImplicitAs(I where .(I.V) = {} and...)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/impl/fail_impl_bad_interface.carbon

@@ -12,7 +12,7 @@
 
 library "[[@TEST_NAME]]";
 
-// CHECK:STDERR: fail_impl_as_false.carbon:[[@LINE+7]]:13: error: cannot implicitly convert value of type `bool` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_impl_as_false.carbon:[[@LINE+7]]:13: error: cannot implicitly convert non-type value of type `bool` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: impl i32 as false {}
 // CHECK:STDERR:             ^~~~~
 // CHECK:STDERR: fail_impl_as_false.carbon:[[@LINE+4]]:13: note: type `bool` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/impl/lookup/min_prelude/impl_cycle.carbon

@@ -134,7 +134,7 @@ fn F() {
   // CHECK:STDERR: fn Compare[T:! type, U:! ComparableWith(T)](t: T, u: U) {}
   // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR:
-  // CHECK:STDERR: fail_impl_cycle_one_generic_param.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `ComparableWith(C)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_impl_cycle_one_generic_param.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `C` into type implementing `ComparableWith(C)` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   Compare({} as C, {} as C);
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_impl_cycle_one_generic_param.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(ComparableWith(C))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/impl/no_prelude/compound.carbon

@@ -44,7 +44,7 @@ impl {.b: ()} as NonInstance2 {
 }
 
 fn NonInstanceCall2(n: {.b: ()}) {
-  // CHECK:STDERR: fail_non-instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `{.b: ()}` to `NonInstance2` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_non-instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `{.b: ()}` into type implementing `NonInstance2` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   n.(NonInstance2.F2)();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_non-instance.carbon:[[@LINE+4]]:3: note: type `{.b: ()}` does not implement interface `Core.ImplicitAs(NonInstance2)` [MissingImplInMemberAccessNote]
@@ -68,7 +68,7 @@ impl {.c: ()} as NonInstance3 {
 }
 
 fn NonInstanceCallIndirect(p: {.c: ()}*) {
-  // CHECK:STDERR: fail_non-instance_indirect.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `{.c: ()}` to `NonInstance3` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_non-instance_indirect.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `{.c: ()}` into type implementing `NonInstance3` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   p->(NonInstance3.F3)();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_non-instance_indirect.carbon:[[@LINE+4]]:3: note: type `{.c: ()}` does not implement interface `Core.ImplicitAs(NonInstance3)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/impl/no_prelude/import_compound.carbon

@@ -50,7 +50,7 @@ import library "lib";
 import Core;
 
 fn NonInstanceCallImportFail(n: {.i: ()}) {
-  // CHECK:STDERR: fail_import_non-instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `{.i: ()}` to `NonInstance` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_import_non-instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `{.i: ()}` into type implementing `NonInstance` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   n.(NonInstance.F)();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_import_non-instance.carbon:[[@LINE+4]]:3: note: type `{.i: ()}` does not implement interface `Core.ImplicitAs(NonInstance)` [MissingImplInMemberAccessNote]
@@ -67,7 +67,7 @@ import library "lib";
 import Core;
 
 fn NonInstanceCallIndirectImport(p: {.i: ()}*) {
-  // CHECK:STDERR: fail_import_non-instance_indirect.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `{.i: ()}` to `NonInstance` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_import_non-instance_indirect.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `{.i: ()}` into type implementing `NonInstance` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   p->(NonInstance.F)();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_import_non-instance_indirect.carbon:[[@LINE+4]]:3: note: type `{.i: ()}` does not implement interface `Core.ImplicitAs(NonInstance)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/impl/no_prelude/interface_args.carbon

@@ -88,7 +88,7 @@ import Core;
 class C {}
 
 fn MakeC() -> C {
-  // CHECK:STDERR: fail_factory.impl.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `type` to `Factory(C)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_factory.impl.carbon:[[@LINE+7]]:10: error: cannot implicitly convert type `A` into type implementing `Factory(C)` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   return A.(Factory(C).Make)();
   // CHECK:STDERR:          ^~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_factory.impl.carbon:[[@LINE+4]]:10: note: type `type` does not implement interface `Core.ImplicitAs(Factory(C))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/impl/use_assoc_const.carbon

@@ -116,7 +116,7 @@ interface J {
 }
 
 fn GenericCallFI32[T:! J where .U = i32](t: T) -> i32 {
-  // CHECK:STDERR: fail_todo_use_where.carbon:[[@LINE+17]]:14: error: cannot implicitly convert value of type `Core.IntLiteral` to `T.(J.U)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_use_where.carbon:[[@LINE+17]]:14: error: cannot implicitly convert value of type `Core.IntLiteral` to `T.(J.U)` [ConversionFailure]
   // CHECK:STDERR:   return t.F(2);
   // CHECK:STDERR:              ^
   // CHECK:STDERR: fail_todo_use_where.carbon:[[@LINE+14]]:14: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(T.(J.U))` [MissingImplInMemberAccessNote]
@@ -126,7 +126,7 @@ fn GenericCallFI32[T:! J where .U = i32](t: T) -> i32 {
   // CHECK:STDERR:   fn F(u: U) -> U;
   // CHECK:STDERR:        ^~~~
   // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_use_where.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `T.(J.U)` to `i32` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_use_where.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `T.(J.U)` to `i32` [ConversionFailure]
   // CHECK:STDERR:   return t.F(2);
   // CHECK:STDERR:   ^~~~~~~~~~~~~~
   // CHECK:STDERR: fail_todo_use_where.carbon:[[@LINE+4]]:3: note: type `T.(J.U)` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]
@@ -146,14 +146,14 @@ interface J {
 
 class E {
   extend impl as J where .U = i32 {
-    // CHECK:STDERR: fail_todo_use_associated_constant_in_impl.carbon:[[@LINE+14]]:13: error: cannot implicitly convert value of type `<associated entity in J>` to `type` [ImplicitAsConversionFailure]
+    // CHECK:STDERR: fail_todo_use_associated_constant_in_impl.carbon:[[@LINE+14]]:13: error: cannot implicitly convert non-type value of type `<associated entity in J>` to `type` [ConversionFailureNonTypeToFacet]
     // CHECK:STDERR:     fn F(u: U) -> U {
     // CHECK:STDERR:             ^
     // CHECK:STDERR: fail_todo_use_associated_constant_in_impl.carbon:[[@LINE+11]]:13: note: type `<associated entity in J>` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]
     // CHECK:STDERR:     fn F(u: U) -> U {
     // CHECK:STDERR:             ^
     // CHECK:STDERR:
-    // CHECK:STDERR: fail_todo_use_associated_constant_in_impl.carbon:[[@LINE+7]]:19: error: cannot implicitly convert value of type `<associated entity in J>` to `type` [ImplicitAsConversionFailure]
+    // CHECK:STDERR: fail_todo_use_associated_constant_in_impl.carbon:[[@LINE+7]]:19: error: cannot implicitly convert non-type value of type `<associated entity in J>` to `type` [ConversionFailureNonTypeToFacet]
     // CHECK:STDERR:     fn F(u: U) -> U {
     // CHECK:STDERR:                   ^
     // CHECK:STDERR: fail_todo_use_associated_constant_in_impl.carbon:[[@LINE+4]]:19: note: type `<associated entity in J>` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]
@@ -283,7 +283,7 @@ fn F() {
   // TODO: `D.(Z.X)` is `C(D)`, but is incorrecty treated only as the symbolic
   // `C(T)` here which fails to convert.
 
-  // CHECK:STDERR: fail_todo_symbolic_associated_type_in_concrete_context.carbon:[[@LINE+7]]:20: error: cannot implicitly convert value of type `C(D)` to `C(T)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_symbolic_associated_type_in_concrete_context.carbon:[[@LINE+7]]:20: error: cannot implicitly convert value of type `C(D)` to `C(T)` [ConversionFailure]
   // CHECK:STDERR:   let a: D.(Z.X) = {} as C(D);
   // CHECK:STDERR:                    ^~~~~~~~~~
   // CHECK:STDERR: fail_todo_symbolic_associated_type_in_concrete_context.carbon:[[@LINE+4]]:20: note: type `C(D)` does not implement interface `Core.ImplicitAs(C(T))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/index/fail_array_non_int_indexing.carbon

@@ -9,7 +9,7 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/index/fail_array_non_int_indexing.carbon
 
 var a: array(i32, 1) = (12,);
-// CHECK:STDERR: fail_array_non_int_indexing.carbon:[[@LINE+7]]:16: error: cannot implicitly convert value of type `f64` to `i32` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_array_non_int_indexing.carbon:[[@LINE+7]]:16: error: cannot implicitly convert value of type `f64` to `i32` [ConversionFailure]
 // CHECK:STDERR: var b: i32 = a[2.6];
 // CHECK:STDERR:                ^~~
 // CHECK:STDERR: fail_array_non_int_indexing.carbon:[[@LINE+4]]:16: note: type `f64` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/interface/fail_assoc_const_bad_default.carbon

@@ -9,7 +9,7 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interface/fail_assoc_const_bad_default.carbon
 
 interface I {
-  // CHECK:STDERR: fail_assoc_const_bad_default.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_assoc_const_bad_default.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   let T:! type = 42;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_assoc_const_bad_default.carbon:[[@LINE+4]]:3: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/interface/min_prelude/compound_member_access.carbon

@@ -56,7 +56,7 @@ fn Simple3(T:! K2, x: T) {
 // Compound member access does not. It tries to convert `y` to `K2`, but only
 // its type `V` can.
 fn Compound3(V:! K2, y: V) {
-  // CHECK:STDERR: fail_caller_instance_interface_not.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `V` to `K2` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_caller_instance_interface_not.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `V` into type implementing `K2` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   y.(K2.Q2)();
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR: fail_caller_instance_interface_not.carbon:[[@LINE+4]]:3: note: type `V` does not implement interface `Core.ImplicitAs(K2)` [MissingImplInMemberAccessNote]
@@ -146,7 +146,7 @@ impl C as A {
 // Since `A.G` is a non-instance method, compound member access may only be
 // used with a type, not an instance.
 fn Fails() {
-  // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `C` to `A` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `C` into type implementing `A` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   ({} as C).((A & A).G)();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+4]]:3: note: type `C` does not implement interface `Core.ImplicitAs(A)` [MissingImplInMemberAccessNote]
@@ -154,7 +154,7 @@ fn Fails() {
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR:
   ({} as C).((A & A).G)();
-  // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `C` to `A` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `C` into type implementing `A` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   (({} as C) as (C as (A & A))).((A & A).G)();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+4]]:3: note: type `C` does not implement interface `Core.ImplicitAs(A)` [MissingImplInMemberAccessNote]
@@ -162,7 +162,7 @@ fn Fails() {
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR:
   (({} as C) as (C as (A & A))).((A & A).G)();
-  // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `C` to `A` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert non-type value of type `C` into type implementing `A` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   (({} as C) as (C as (A & A))).(A.G)();
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_combine_non_instance.carbon:[[@LINE+4]]:3: note: type `C` does not implement interface `Core.ImplicitAs(A)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/interface/no_prelude/fail_assoc_const_alias.carbon

@@ -26,7 +26,7 @@ interface I {
 
 interface J {
   alias U = I.T;
-  // CHECK:STDERR: fail_alias_to_different_interface.carbon:[[@LINE+7]]:13: error: cannot implicitly convert value of type `J` to `I` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_alias_to_different_interface.carbon:[[@LINE+7]]:13: error: cannot implicitly convert type `Self` that implements `J` into type implementing `I` [ConversionFailureFacetToFacet]
   // CHECK:STDERR:   fn F() -> U;
   // CHECK:STDERR:             ^
   // CHECK:STDERR: fail_alias_to_different_interface.carbon:[[@LINE+4]]:13: note: type `J` does not implement interface `Core.ImplicitAs(I)` [MissingImplInMemberAccessNote]
@@ -51,7 +51,7 @@ impl forall [V:! J2] V as I2 where .T2 = () {}
 
 interface J2 {
   alias U2 = I2.T2;
-  // CHECK:STDERR: fail_todo_alias_to_different_interface_with_requires.carbon:[[@LINE+7]]:14: error: cannot implicitly convert value of type `J2` to `I2` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_alias_to_different_interface_with_requires.carbon:[[@LINE+7]]:14: error: cannot implicitly convert type `Self` that implements `J2` into type implementing `I2` [ConversionFailureFacetToFacet]
   // CHECK:STDERR:   fn F2() -> U2;
   // CHECK:STDERR:              ^~
   // CHECK:STDERR: fail_todo_alias_to_different_interface_with_requires.carbon:[[@LINE+4]]:14: note: type `J2` does not implement interface `Core.ImplicitAs(I2)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/interface/no_prelude/fail_member_lookup.carbon

@@ -33,7 +33,7 @@ fn F() {
   // CHECK:STDERR:
   Interface.F();
 
-  // CHECK:STDERR: fail_member_lookup.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `<associated entity in Interface>` to `type` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_member_lookup.carbon:[[@LINE+7]]:10: error: cannot implicitly convert non-type value of type `<associated entity in Interface>` to `type` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   var v: Interface.T;
   // CHECK:STDERR:          ^~~~~~~~~~~
   // CHECK:STDERR: fail_member_lookup.carbon:[[@LINE+4]]:10: note: type `<associated entity in Interface>` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]
@@ -45,7 +45,7 @@ fn F() {
 
 interface Different {}
 
-// CHECK:STDERR: fail_member_lookup.carbon:[[@LINE+7]]:24: error: cannot implicitly convert value of type `Different` to `Interface` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_member_lookup.carbon:[[@LINE+7]]:24: error: cannot implicitly convert type `U` that implements `Different` into type implementing `Interface` [ConversionFailureFacetToFacet]
 // CHECK:STDERR: fn G(U:! Different) -> U.(Interface.T);
 // CHECK:STDERR:                        ^~~~~~~~~~~~~~~
 // CHECK:STDERR: fail_member_lookup.carbon:[[@LINE+4]]:24: note: type `Different` does not implement interface `Core.ImplicitAs(Interface)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/let/fail_generic.carbon

@@ -11,7 +11,7 @@
 // TODO: Should this be valid?
 fn F(a: i32) -> i32 {
   let T:! type = i32;
-  // CHECK:STDERR: fail_generic.carbon:[[@LINE+7]]:14: error: cannot implicitly convert value of type `Core.IntLiteral` to `T` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_generic.carbon:[[@LINE+7]]:14: error: cannot implicitly convert value of type `Core.IntLiteral` to `T` [ConversionFailure]
   // CHECK:STDERR:   let x: T = 5;
   // CHECK:STDERR:              ^
   // CHECK:STDERR: fail_generic.carbon:[[@LINE+4]]:14: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(T)` [MissingImplInMemberAccessNote]
@@ -19,7 +19,7 @@ fn F(a: i32) -> i32 {
   // CHECK:STDERR:              ^
   // CHECK:STDERR:
   let x: T = 5;
-  // CHECK:STDERR: fail_generic.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `T` to `i32` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_generic.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `T` to `i32` [ConversionFailure]
   // CHECK:STDERR:   return x;
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR: fail_generic.carbon:[[@LINE+4]]:3: note: type `T` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/operators/builtin/fail_type_mismatch.carbon

@@ -9,7 +9,7 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/operators/builtin/fail_type_mismatch.carbon
 
 fn Main() {
-  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:17: error: cannot implicitly convert value of type `Core.IntLiteral` to `bool` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:17: error: cannot implicitly convert value of type `Core.IntLiteral` to `bool` [ConversionFailure]
   // CHECK:STDERR:   var x: bool = not 12;
   // CHECK:STDERR:                 ^~~~~~
   // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+4]]:17: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(bool)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/operators/builtin/fail_type_mismatch_assignment.carbon

@@ -10,7 +10,7 @@
 
 fn Main() {
   var a: i32 = 3;
-  // CHECK:STDERR: fail_type_mismatch_assignment.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `f64` to `i32` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_type_mismatch_assignment.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `f64` to `i32` [ConversionFailure]
   // CHECK:STDERR:   a = 5.6;
   // CHECK:STDERR:   ^~~~~~~
   // CHECK:STDERR: fail_type_mismatch_assignment.carbon:[[@LINE+4]]:3: note: type `f64` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/operators/overloaded/eq.carbon

@@ -62,7 +62,7 @@ impl C as Core.Eq {
 }
 
 fn TestRhsBad(a: C, b: D) -> bool {
-  // CHECK:STDERR: fail_no_impl_for_args.carbon:[[@LINE+10]]:15: error: cannot implicitly convert value of type `D` to `C` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_no_impl_for_args.carbon:[[@LINE+10]]:15: error: cannot implicitly convert value of type `D` to `C` [ConversionFailure]
   // CHECK:STDERR:   return a == b;
   // CHECK:STDERR:               ^
   // CHECK:STDERR: fail_no_impl_for_args.carbon:[[@LINE+7]]:15: note: type `D` does not implement interface `Core.ImplicitAs(C)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/operators/overloaded/fail_no_impl_for_arg.carbon

@@ -21,7 +21,7 @@ impl C as Core.AddAssign {
 }
 
 fn Test(a: C, b: D) -> C {
-  // CHECK:STDERR: fail_no_impl_for_arg.carbon:[[@LINE+10]]:14: error: cannot implicitly convert value of type `D` to `C` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_no_impl_for_arg.carbon:[[@LINE+10]]:14: error: cannot implicitly convert value of type `D` to `C` [ConversionFailure]
   // CHECK:STDERR:   return a + b;
   // CHECK:STDERR:              ^
   // CHECK:STDERR: fail_no_impl_for_arg.carbon:[[@LINE+7]]:14: note: type `D` does not implement interface `Core.ImplicitAs(C)` [MissingImplInMemberAccessNote]
@@ -36,7 +36,7 @@ fn Test(a: C, b: D) -> C {
 
 fn TestAssign(b: D) {
   var a: C = {};
-  // CHECK:STDERR: fail_no_impl_for_arg.carbon:[[@LINE+10]]:8: error: cannot implicitly convert value of type `D` to `C` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_no_impl_for_arg.carbon:[[@LINE+10]]:8: error: cannot implicitly convert value of type `D` to `C` [ConversionFailure]
   // CHECK:STDERR:   a += b;
   // CHECK:STDERR:        ^
   // CHECK:STDERR: fail_no_impl_for_arg.carbon:[[@LINE+7]]:8: note: type `D` does not implement interface `Core.ImplicitAs(C)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/operators/overloaded/index.carbon

@@ -54,7 +54,7 @@ impl C as Core.IndexWith(SubscriptType, ElementType) {
 }
 
 let c: C = {};
-// CHECK:STDERR: fail_invalid_subscript_type.carbon:[[@LINE+7]]:22: error: cannot implicitly convert value of type `Core.IntLiteral` to `SubscriptType` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_invalid_subscript_type.carbon:[[@LINE+7]]:22: error: cannot implicitly convert value of type `Core.IntLiteral` to `SubscriptType` [ConversionFailure]
 // CHECK:STDERR: let x: ElementType = c[0];
 // CHECK:STDERR:                      ^~~~
 // CHECK:STDERR: fail_invalid_subscript_type.carbon:[[@LINE+4]]:22: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(SubscriptType)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/pointer/fail_type_mismatch.carbon

@@ -9,7 +9,7 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/pointer/fail_type_mismatch.carbon
 
 fn ConstMismatch(p: const {}*) -> const ({}*) {
-  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `const {}*` to `const ({}*)` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `const {}*` to `const ({}*)` [ConversionFailure]
   // CHECK:STDERR:   return p;
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+4]]:3: note: type `const {}*` does not implement interface `Core.ImplicitAs(const ({}*))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/return/fail_type_mismatch.carbon

@@ -9,7 +9,7 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/return/fail_type_mismatch.carbon
 
 fn Main() -> i32 {
-  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `f64` to `i32` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+7]]:3: error: cannot implicitly convert value of type `f64` to `i32` [ConversionFailure]
   // CHECK:STDERR:   return 1.0;
   // CHECK:STDERR:   ^~~~~~~~~~~
   // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+4]]:3: note: type `f64` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/struct/fail_type_assign.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/struct/fail_type_assign.carbon
 
-// CHECK:STDERR: fail_type_assign.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `type` to `{.a: i32}` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_type_assign.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `type` to `{.a: i32}` [ConversionFailure]
 // CHECK:STDERR: var x: {.a: i32} = {.a: i32};
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~
 // CHECK:STDERR: fail_type_assign.carbon:[[@LINE+4]]:1: note: type `type` does not implement interface `Core.ImplicitAs({.a: i32})` [MissingImplInMemberAccessNote]

toolchain/check/testdata/struct/fail_value_as_type.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/struct/fail_value_as_type.carbon
 
-// CHECK:STDERR: fail_value_as_type.carbon:[[@LINE+7]]:8: error: cannot implicitly convert value of type `{.a: Core.IntLiteral}` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_value_as_type.carbon:[[@LINE+7]]:8: error: cannot implicitly convert non-type value of type `{.a: Core.IntLiteral}` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: var x: {.a = 1};
 // CHECK:STDERR:        ^~~~~~~~
 // CHECK:STDERR: fail_value_as_type.carbon:[[@LINE+4]]:8: note: type `{.a: Core.IntLiteral}` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/struct/import.carbon

@@ -43,7 +43,7 @@ var c_bad: C({.c = 1, .d = 2}) = F();
 // --- fail_bad_value.impl.carbon
 
 impl package Implicit;
-// CHECK:STDERR: fail_bad_value.impl.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `C({.a = 1, .b = 2})` to `C({.a = 3, .b = 4})` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_bad_value.impl.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `C({.a = 1, .b = 2})` to `C({.a = 3, .b = 4})` [ConversionFailure]
 // CHECK:STDERR: var c_bad: C({.a = 3, .b = 4}) = F();
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR: fail_bad_value.impl.carbon:[[@LINE+4]]:1: note: type `C({.a = 1, .b = 2})` does not implement interface `Core.ImplicitAs(C({.a = 3, .b = 4}))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/tuple/access/fail_non_int_indexing.carbon

@@ -9,7 +9,7 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/tuple/access/fail_non_int_indexing.carbon
 
 var a: (i32, i32) = (12, 6);
-// CHECK:STDERR: fail_non_int_indexing.carbon:[[@LINE+7]]:17: error: cannot implicitly convert value of type `f64` to `Core.IntLiteral` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_non_int_indexing.carbon:[[@LINE+7]]:17: error: cannot implicitly convert value of type `f64` to `Core.IntLiteral` [ConversionFailure]
 // CHECK:STDERR: var b: i32 = a.(2.6);
 // CHECK:STDERR:                 ^~~
 // CHECK:STDERR: fail_non_int_indexing.carbon:[[@LINE+4]]:17: note: type `f64` does not implement interface `Core.ImplicitAs(Core.IntLiteral)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/tuple/fail_element_type_mismatch.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/tuple/fail_element_type_mismatch.carbon
 
-// CHECK:STDERR: fail_element_type_mismatch.carbon:[[@LINE+7]]:21: error: cannot implicitly convert value of type `f64` to `i32` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_element_type_mismatch.carbon:[[@LINE+7]]:21: error: cannot implicitly convert value of type `f64` to `i32` [ConversionFailure]
 // CHECK:STDERR: var x: (i32, i32) = (2, 65.89);
 // CHECK:STDERR:                     ^~~~~~~~~~
 // CHECK:STDERR: fail_element_type_mismatch.carbon:[[@LINE+4]]:21: note: type `f64` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/tuple/fail_type_assign.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/tuple/fail_type_assign.carbon
 
-// CHECK:STDERR: fail_type_assign.carbon:[[@LINE+7]]:18: error: cannot implicitly convert value of type `type` to `i32` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_type_assign.carbon:[[@LINE+7]]:18: error: cannot implicitly convert value of type `type` to `i32` [ConversionFailure]
 // CHECK:STDERR: var x: (i32, ) = (i32, );
 // CHECK:STDERR:                  ^~~~~~~
 // CHECK:STDERR: fail_type_assign.carbon:[[@LINE+4]]:18: note: type `type` does not implement interface `Core.ImplicitAs(i32)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/tuple/fail_value_as_type.carbon

@@ -8,7 +8,7 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/tuple/fail_value_as_type.carbon
 
-// CHECK:STDERR: fail_value_as_type.carbon:[[@LINE+7]]:8: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_value_as_type.carbon:[[@LINE+7]]:8: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: var x: (1, );
 // CHECK:STDERR:        ^~~~~
 // CHECK:STDERR: fail_value_as_type.carbon:[[@LINE+4]]:8: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/tuple/import.carbon

@@ -45,7 +45,7 @@ var c_bad: C((1, 2, 3)) = F();
 
 impl package Implicit;
 
-// CHECK:STDERR: fail_bad_value.impl.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `C((1, 2))` to `C((3, 4))` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_bad_value.impl.carbon:[[@LINE+7]]:1: error: cannot implicitly convert value of type `C((1, 2))` to `C((3, 4))` [ConversionFailure]
 // CHECK:STDERR: var c_bad: C((3, 4)) = F();
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~
 // CHECK:STDERR: fail_bad_value.impl.carbon:[[@LINE+4]]:1: note: type `C((1, 2))` does not implement interface `Core.ImplicitAs(C((3, 4)))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/var/fail_storage_is_literal.carbon

@@ -9,7 +9,7 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/var/fail_storage_is_literal.carbon
 
 fn Main() {
-  // CHECK:STDERR: fail_storage_is_literal.carbon:[[@LINE+7]]:10: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_storage_is_literal.carbon:[[@LINE+7]]:10: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
   // CHECK:STDERR:   var x: 1 = 1;
   // CHECK:STDERR:          ^
   // CHECK:STDERR: fail_storage_is_literal.carbon:[[@LINE+4]]:10: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/where_expr/constraints.carbon

@@ -42,7 +42,7 @@ fn AssociatedTypeImpls(W:! K where .Associated impls M);
 
 library "[[@TEST_NAME]]";
 
-// CHECK:STDERR: fail_left_of_impls_non_type.carbon:[[@LINE+7]]:32: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_left_of_impls_non_type.carbon:[[@LINE+7]]:32: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: fn NonTypeImpls(U:! type where 7 impls type);
 // CHECK:STDERR:                                ^
 // CHECK:STDERR: fail_left_of_impls_non_type.carbon:[[@LINE+4]]:32: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]
@@ -55,7 +55,7 @@ fn NonTypeImpls(U:! type where 7 impls type);
 
 library "[[@TEST_NAME]]";
 
-// CHECK:STDERR: fail_right_of_impls_non_type.carbon:[[@LINE+7]]:44: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_right_of_impls_non_type.carbon:[[@LINE+7]]:44: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: fn ImplsNonType(U:! type where .Self impls 7);
 // CHECK:STDERR:                                            ^
 // CHECK:STDERR: fail_right_of_impls_non_type.carbon:[[@LINE+4]]:44: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]
@@ -86,7 +86,7 @@ impl C as J {}
 
 // TODO: Should report that `C` does not meet the constraint.
 fn DoesNotImplI() {
-  // CHECK:STDERR: fail_todo_enforce_constraint.carbon:[[@LINE+11]]:3: error: cannot implicitly convert value of type `type` to `J where...` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_enforce_constraint.carbon:[[@LINE+11]]:3: error: cannot implicitly convert type `C` into type implementing `J where...` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   Impls(C);
   // CHECK:STDERR:   ^~~~~~~~
   // CHECK:STDERR: fail_todo_enforce_constraint.carbon:[[@LINE+8]]:3: note: type `type` does not implement interface `Core.ImplicitAs(J where...)` [MissingImplInMemberAccessNote]
@@ -104,7 +104,7 @@ fn EmptyStruct(Y:! J where .Self == {});
 
 // TODO: Should report that `C` does not meeet the constraint.
 fn NotEmptyStruct() {
-  // CHECK:STDERR: fail_todo_enforce_constraint.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `type` to `J where...` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_todo_enforce_constraint.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `C` into type implementing `J where...` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   EmptyStruct(C);
   // CHECK:STDERR:   ^~~~~~~~~~~~~~
   // CHECK:STDERR: fail_todo_enforce_constraint.carbon:[[@LINE+7]]:3: note: type `type` does not implement interface `Core.ImplicitAs(J where...)` [MissingImplInMemberAccessNote]

toolchain/check/testdata/where_expr/equal_rewrite.carbon

@@ -73,7 +73,7 @@ interface O {
 fn WithInteger(Q:! O where .P = i32) {}
 
 fn WithBool(R:! O where .P = bool) {
-  // CHECK:STDERR: fail_rewrites_mismatch_right.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `O where .(O.P) = bool` to `O where .(O.P) = i32` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_rewrites_mismatch_right.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `R` that implements `O where .(O.P) = bool` into type implementing `O where .(O.P) = i32` [ConversionFailureFacetToFacet]
   // CHECK:STDERR:   WithInteger(R);
   // CHECK:STDERR:   ^~~~~~~~~~~~~~
   // CHECK:STDERR: fail_rewrites_mismatch_right.carbon:[[@LINE+7]]:3: note: type `O where .(O.P) = bool` does not implement interface `Core.ImplicitAs(O where .(O.P) = i32)` [MissingImplInMemberAccessNote]
@@ -98,7 +98,7 @@ interface S {
 fn WithT(V:! S where .T = ()) {}
 
 fn WithU(W:! S where .U = ()) {
-  // CHECK:STDERR: fail_rewrites_mismatch_left.carbon:[[@LINE+10]]:3: error: cannot implicitly convert value of type `S where .(S.U) = ()` to `S where .(S.T) = ()` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_rewrites_mismatch_left.carbon:[[@LINE+10]]:3: error: cannot implicitly convert type `W` that implements `S where .(S.U) = ()` into type implementing `S where .(S.T) = ()` [ConversionFailureFacetToFacet]
   // CHECK:STDERR:   WithT(W);
   // CHECK:STDERR:   ^~~~~~~~
   // CHECK:STDERR: fail_rewrites_mismatch_left.carbon:[[@LINE+7]]:3: note: type `S where .(S.U) = ()` does not implement interface `Core.ImplicitAs(S where .(S.T) = ())` [MissingImplInMemberAccessNote]
@@ -119,7 +119,7 @@ import library "equal_constraint";
 import library "nested_rewrites";
 
 fn Calls() {
-  // CHECK:STDERR: fail_import_rewrites.carbon:[[@LINE+11]]:3: error: cannot implicitly convert value of type `type` to `N where .(N.P) = {}` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_import_rewrites.carbon:[[@LINE+11]]:3: error: cannot implicitly convert type `bool` into type implementing `N where .(N.P) = {}` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   Equal(bool);
   // CHECK:STDERR:   ^~~~~~~~~~~
   // CHECK:STDERR: fail_import_rewrites.carbon:[[@LINE+8]]:3: note: type `type` does not implement interface `Core.ImplicitAs(N where .(N.P) = {})` [MissingImplInMemberAccessNote]
@@ -132,7 +132,7 @@ fn Calls() {
   // CHECK:STDERR:
   Equal(bool);
 
-  // CHECK:STDERR: fail_import_rewrites.carbon:[[@LINE+11]]:3: error: cannot implicitly convert value of type `type` to `A where .(A.C) = () and .(A.B) = bool` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_import_rewrites.carbon:[[@LINE+11]]:3: error: cannot implicitly convert type `i32` into type implementing `A where .(A.C) = () and .(A.B) = bool` [ConversionFailureTypeToFacet]
   // CHECK:STDERR:   NestedRewrite(i32);
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_import_rewrites.carbon:[[@LINE+8]]:3: note: type `type` does not implement interface `Core.ImplicitAs(A where .(A.C) = () and .(A.B) = bool)` [MissingImplInMemberAccessNote]
@@ -155,7 +155,7 @@ interface I {
 }
 
 // `2` can't be converted to the type of `I.Member`
-// CHECK:STDERR: fail_check_rewrite_constraints.carbon:[[@LINE+7]]:46: error: cannot implicitly convert value of type `Core.IntLiteral` to `type` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_check_rewrite_constraints.carbon:[[@LINE+7]]:46: error: cannot implicitly convert non-type value of type `Core.IntLiteral` to `type` [ConversionFailureNonTypeToFacet]
 // CHECK:STDERR: fn RewriteTypeMismatch(X:! I where .Member = 2);
 // CHECK:STDERR:                                              ^
 // CHECK:STDERR: fail_check_rewrite_constraints.carbon:[[@LINE+4]]:46: note: type `Core.IntLiteral` does not implement interface `Core.ImplicitAs(type)` [MissingImplInMemberAccessNote]
@@ -172,7 +172,7 @@ interface A {}
 class D {}
 impl D as A {}
 // TODO: This should be a compile-time binding, once that is supported.
-// CHECK:STDERR: fail_todo_let.carbon:[[@LINE+7]]:35: error: cannot implicitly convert value of type `type` to `type where...` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_todo_let.carbon:[[@LINE+7]]:35: error: cannot implicitly convert type `D` into type implementing `type where...` [ConversionFailureTypeToFacet]
 // CHECK:STDERR: let B: type where .Self impls A = D;
 // CHECK:STDERR:                                   ^
 // CHECK:STDERR: fail_todo_let.carbon:[[@LINE+4]]:35: note: type `type` does not implement interface `Core.ImplicitAs(type where...)` [MissingImplInMemberAccessNote]
@@ -192,7 +192,7 @@ interface E {
 // Testing how these types get stringified in error messages.
 
 // TODO: This should be a compile-time binding, once that is supported.
-// CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+7]]:42: error: cannot implicitly convert value of type `type` to `E where .(E.G) = () and .(E.F) = bool` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+7]]:42: error: cannot implicitly convert type `f64` into type implementing `E where .(E.G) = () and .(E.F) = bool` [ConversionFailureTypeToFacet]
 // CHECK:STDERR: let H: (E where .F = bool and .G = ()) = f64;
 // CHECK:STDERR:                                          ^~~
 // CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+4]]:42: note: type `type` does not implement interface `Core.ImplicitAs(E where .(E.G) = () and .(E.F) = bool)` [MissingImplInMemberAccessNote]
@@ -201,7 +201,7 @@ interface E {
 // CHECK:STDERR:
 let H: (E where .F = bool and .G = ()) = f64;
 
-// CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+7]]:45: error: cannot implicitly convert value of type `type` to `E where .(E.G) = i32 and .(E.F) = {}` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+7]]:45: error: cannot implicitly convert type `bool` into type implementing `E where .(E.G) = i32 and .(E.F) = {}` [ConversionFailureTypeToFacet]
 // CHECK:STDERR: let J: ((E where .F = {}) where .G = i32) = bool;
 // CHECK:STDERR:                                             ^~~~
 // CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+4]]:45: note: type `type` does not implement interface `Core.ImplicitAs(E where .(E.G) = i32 and .(E.F) = {})` [MissingImplInMemberAccessNote]
@@ -210,7 +210,7 @@ let H: (E where .F = bool and .G = ()) = f64;
 // CHECK:STDERR:
 let J: ((E where .F = {}) where .G = i32) = bool;
 
-// CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+7]]:33: error: cannot implicitly convert value of type `type` to `E where .(E.F) = .(E.G)` [ImplicitAsConversionFailure]
+// CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+7]]:33: error: cannot implicitly convert type `bool` into type implementing `E where .(E.F) = .(E.G)` [ConversionFailureTypeToFacet]
 // CHECK:STDERR: let K: (E where .F = .Self.G) = bool;
 // CHECK:STDERR:                                 ^~~~
 // CHECK:STDERR: fail_type_does_not_implement_where.carbon:[[@LINE+4]]:33: note: type `type` does not implement interface `Core.ImplicitAs(E where .(E.F) = .(E.G))` [MissingImplInMemberAccessNote]

toolchain/check/testdata/while/fail_bad_condition.carbon

@@ -9,7 +9,7 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/while/fail_bad_condition.carbon
 
 fn While() {
-  // CHECK:STDERR: fail_bad_condition.carbon:[[@LINE+7]]:9: error: cannot implicitly convert value of type `String` to `bool` [ImplicitAsConversionFailure]
+  // CHECK:STDERR: fail_bad_condition.carbon:[[@LINE+7]]:9: error: cannot implicitly convert value of type `String` to `bool` [ConversionFailure]
   // CHECK:STDERR:   while ("Hello") {}
   // CHECK:STDERR:         ^~~~~~~~~
   // CHECK:STDERR: fail_bad_condition.carbon:[[@LINE+4]]:9: note: type `String` does not implement interface `Core.ImplicitAs(bool)` [MissingImplInMemberAccessNote]

toolchain/diagnostics/diagnostic_kind.def

@@ -408,8 +408,10 @@ CARBON_DIAGNOSTIC_KIND(ReturnStatementDisallowExpr)
 CARBON_DIAGNOSTIC_KIND(ReturnTypeHereNote)
 CARBON_DIAGNOSTIC_KIND(ReturnTypeOmittedNote)
 CARBON_DIAGNOSTIC_KIND(ReturnStatementMissingExpr)
-CARBON_DIAGNOSTIC_KIND(ImplicitAsConversionFailure)
-CARBON_DIAGNOSTIC_KIND(ExplicitAsConversionFailure)
+CARBON_DIAGNOSTIC_KIND(ConversionFailure)
+CARBON_DIAGNOSTIC_KIND(ConversionFailureNonTypeToFacet)
+CARBON_DIAGNOSTIC_KIND(ConversionFailureFacetToFacet)
+CARBON_DIAGNOSTIC_KIND(ConversionFailureTypeToFacet)
 CARBON_DIAGNOSTIC_KIND(TypeExprEvaluationFailure)
 CARBON_DIAGNOSTIC_KIND(UnexpectedDeclNameParams)
 CARBON_DIAGNOSTIC_KIND(QualifiedNameInNonScope)