Fix crash when importing an invalid impl (#5875)

Dropping this in with basic.carbon as an aspirational way to encourage
more tests there.

This currently crashes because `CollectCandidateImplsForQuery` tries
building a type structure which cannot contain `ErrorInst`.

toolchain/check/testdata/impl/basic.carbon

@@ -3,8 +3,6 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // INCLUDE-FILE: toolchain/testing/testdata/min_prelude/none.carbon
-// TODO: Add ranges and switch to "--dump-sem-ir-ranges=only".
-// EXTRA-ARGS: --dump-sem-ir-ranges=if-present
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
@@ -12,41 +10,67 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/impl/basic.carbon
 
+// --- basic.carbon
+
+library "[[@TEST_NAME]]";
+
 interface Simple {
   fn F();
 }
 
 class C {}
 
+//@dump-sem-ir-begin
 impl C as Simple {
   fn F() {}
 }
+//@dump-sem-ir-end
+
+// --- fail_invalid_impl.carbon
+
+library "[[@TEST_NAME]]";
+
+interface I {
+  fn Op[self: Self]();
+}
+
+class C {}
+
+// This produces an invalid impl.
+// CHECK:STDERR: fail_invalid_impl.carbon:[[@LINE+4]]:6: error: name `Unknown` not found [NameNotFound]
+// CHECK:STDERR: impl Unknown as I {
+// CHECK:STDERR:      ^~~~~~~
+// CHECK:STDERR:
+impl Unknown as I {
+  fn Op[self: Self]() {}
+}
+
+// --- fail_import_invalid_impl.carbon
+
+library "[[@TEST_NAME]]";
+import library "invalid_impl";
+
+fn F() {
+  // This impl doesn't exist, but it still tests that we can ignore the
+  // `impl Unknown as I` on import.
+  // CHECK:STDERR: fail_import_invalid_impl.carbon:[[@LINE+4]]:3: error: cannot access member of interface `I` in type `type` that does not implement that interface [MissingImplInMemberAccess]
+  // CHECK:STDERR:   C.(I.Op)();
+  // CHECK:STDERR:   ^~~~~~~~
+  // CHECK:STDERR:
+  C.(I.Op)();
+}
 
 // CHECK:STDOUT: --- basic.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %Simple.type: type = facet_type <@Simple> [concrete]
-// CHECK:STDOUT:   %Self: %Simple.type = bind_symbolic_name Self, 0 [symbolic]
-// CHECK:STDOUT:   %Simple.F.type: type = fn_type @Simple.F [concrete]
-// CHECK:STDOUT:   %Simple.F: %Simple.F.type = struct_value () [concrete]
-// CHECK:STDOUT:   %Simple.assoc_type: type = assoc_entity_type @Simple [concrete]
-// CHECK:STDOUT:   %assoc0: %Simple.assoc_type = assoc_entity element0, @Simple.%Simple.F.decl [concrete]
 // CHECK:STDOUT:   %C: type = class_type @C [concrete]
-// CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [concrete]
-// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [concrete]
 // CHECK:STDOUT:   %Simple.impl_witness: <witness> = impl_witness file.%Simple.impl_witness_table [concrete]
 // CHECK:STDOUT:   %C.as.Simple.impl.F.type: type = fn_type @C.as.Simple.impl.F [concrete]
 // CHECK:STDOUT:   %C.as.Simple.impl.F: %C.as.Simple.impl.F.type = struct_value () [concrete]
-// CHECK:STDOUT:   %Simple.facet: %Simple.type = facet_value %C, (%Simple.impl_witness) [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: file {
-// CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
-// CHECK:STDOUT:     .Simple = %Simple.decl
-// CHECK:STDOUT:     .C = %C.decl
-// CHECK:STDOUT:   }
-// CHECK:STDOUT:   %Simple.decl: type = interface_decl @Simple [concrete = constants.%Simple.type] {} {}
-// CHECK:STDOUT:   %C.decl: type = class_decl @C [concrete = constants.%C] {} {}
 // CHECK:STDOUT:   impl_decl @C.as.Simple.impl [concrete] {} {
 // CHECK:STDOUT:     %C.ref: type = name_ref C, file.%C.decl [concrete = constants.%C]
 // CHECK:STDOUT:     %Simple.ref: type = name_ref Simple, file.%Simple.decl [concrete = constants.%Simple.type]
@@ -55,17 +79,6 @@ impl C as Simple {
 // CHECK:STDOUT:   %Simple.impl_witness: <witness> = impl_witness %Simple.impl_witness_table [concrete = constants.%Simple.impl_witness]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: interface @Simple {
-// CHECK:STDOUT:   %Self: %Simple.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self]
-// CHECK:STDOUT:   %Simple.F.decl: %Simple.F.type = fn_decl @Simple.F [concrete = constants.%Simple.F] {} {}
-// CHECK:STDOUT:   %assoc0: %Simple.assoc_type = assoc_entity element0, %Simple.F.decl [concrete = constants.%assoc0]
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = %Self
-// CHECK:STDOUT:   .F = %assoc0
-// CHECK:STDOUT:   witness = (%Simple.F.decl)
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: impl @C.as.Simple.impl: %C.ref as %Simple.ref {
 // CHECK:STDOUT:   %C.as.Simple.impl.F.decl: %C.as.Simple.impl.F.type = fn_decl @C.as.Simple.impl.F [concrete = constants.%C.as.Simple.impl.F] {} {}
 // CHECK:STDOUT:
@@ -74,25 +87,8 @@ impl C as Simple {
 // CHECK:STDOUT:   witness = file.%Simple.impl_witness
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: class @C {
-// CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [concrete = constants.%empty_struct_type]
-// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [concrete = constants.%complete_type]
-// CHECK:STDOUT:   complete_type_witness = %complete_type
-// CHECK:STDOUT:
-// CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = constants.%C
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
-// CHECK:STDOUT: generic fn @Simple.F(@Simple.%Self: %Simple.type) {
-// CHECK:STDOUT:   fn();
-// CHECK:STDOUT: }
-// CHECK:STDOUT:
 // CHECK:STDOUT: fn @C.as.Simple.impl.F() {
 // CHECK:STDOUT: !entry:
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: specific @Simple.F(constants.%Self) {}
-// CHECK:STDOUT:
-// CHECK:STDOUT: specific @Simple.F(constants.%Simple.facet) {}
-// CHECK:STDOUT:

toolchain/sem_ir/type_iterator.cpp

@@ -79,6 +79,7 @@ auto TypeIterator::Next() -> Step {
 
       case SemIR::AssociatedEntityType::Kind:
       case SemIR::BoolType::Kind:
+      case SemIR::ErrorInst::Kind:
       case SemIR::FacetType::Kind:
       case SemIR::FloatType::Kind:
       case SemIR::FunctionType::Kind: