Adopt new diagnostic conventions in handle_class.cpp (#4327)

Doing this to a couple of diagnostics was suggested in review comments
on #4320, so I've applied the suggestions across the whole file.

---------

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>

toolchain/check/handle_class.cpp

@@ -79,9 +79,9 @@ static auto MergeClassRedecl(Context& context, SemIRLoc new_loc,
   // TODO: The rule here is not yet decided. See #3384.
   if (prev_class.inheritance_kind != new_class.inheritance_kind) {
     CARBON_DIAGNOSTIC(ClassRedeclarationDifferentIntroducer, Error,
-                      "Class redeclared with different inheritance kind.");
+                      "class redeclared with different inheritance kind");
     CARBON_DIAGNOSTIC(ClassRedeclarationDifferentIntroducerPrevious, Note,
-                      "Previously declared here.");
+                      "previously declared here");
     context.emitter()
         .Build(new_loc, ClassRedeclarationDifferentIntroducer)
         .Note(prev_loc, ClassRedeclarationDifferentIntroducerPrevious)
@@ -322,8 +322,7 @@ static auto DiagnoseClassSpecificDeclOutsideClass(Context& context,
                                                   SemIRLoc loc,
                                                   Lex::TokenKind tok) -> void {
   CARBON_DIAGNOSTIC(ClassSpecificDeclOutsideClass, Error,
-                    "`{0}` declaration can only be used in a class.",
-                    Lex::TokenKind);
+                    "`{0}` declaration outside class", Lex::TokenKind);
   context.emitter().Emit(loc, ClassSpecificDeclOutsideClass, tok);
 }
 
@@ -345,16 +344,17 @@ static auto DiagnoseClassSpecificDeclRepeated(Context& context,
                                               SemIRLoc new_loc,
                                               SemIRLoc prev_loc,
                                               Lex::TokenKind tok) -> void {
-  CARBON_DIAGNOSTIC(ClassSpecificDeclRepeated, Error,
-                    "Multiple `{0}` declarations in class.{1}", Lex::TokenKind,
-                    std::string);
-  const llvm::StringRef extra = tok == Lex::TokenKind::Base
-                                    ? " Multiple inheritance is not permitted."
-                                    : "";
+  CARBON_DIAGNOSTIC(AdaptDeclRepeated, Error,
+                    "multiple `adapt` declarations in class");
+  CARBON_DIAGNOSTIC(BaseDeclRepeated, Error,
+                    "multiple `base` declarations in class; multiple "
+                    "inheritance is not permitted");
   CARBON_DIAGNOSTIC(ClassSpecificDeclPrevious, Note,
-                    "Previous `{0}` declaration is here.", Lex::TokenKind);
+                    "previous `{0}` declaration is here", Lex::TokenKind);
+  CARBON_CHECK(tok == Lex::TokenKind::Adapt || tok == Lex::TokenKind::Base);
   context.emitter()
-      .Build(new_loc, ClassSpecificDeclRepeated, tok, extra.str())
+      .Build(new_loc, tok == Lex::TokenKind::Adapt ? AdaptDeclRepeated
+                                                   : BaseDeclRepeated)
       .Note(prev_loc, ClassSpecificDeclPrevious, tok)
       .Emit();
 }
@@ -390,7 +390,7 @@ auto HandleParseNode(Context& context, Parse::AdaptDeclId node_id) -> bool {
   auto adapted_type_id = ExprAsType(context, node_id, adapted_type_expr_id);
   adapted_type_id = context.AsCompleteType(adapted_type_id, [&] {
     CARBON_DIAGNOSTIC(IncompleteTypeInAdaptDecl, Error,
-                      "Adapted type `{0}` is an incomplete type.",
+                      "adapted type `{0}` is an incomplete type",
                       SemIR::TypeId);
     return context.emitter().Build(node_id, IncompleteTypeInAdaptDecl,
                                    adapted_type_id);
@@ -454,8 +454,8 @@ constexpr BaseInfo BaseInfo::Error = {.type_id = SemIR::TypeId::Error,
 static auto DiagnoseBaseIsFinal(Context& context, Parse::NodeId node_id,
                                 SemIR::TypeId base_type_id) -> void {
   CARBON_DIAGNOSTIC(BaseIsFinal, Error,
-                    "Deriving from final type `{0}`. Base type must be an "
-                    "`abstract` or `base` class.",
+                    "deriving from final type `{0}`; base type must be an "
+                    "`abstract` or `base` class",
                     SemIR::TypeId);
   context.emitter().Emit(node_id, BaseIsFinal, base_type_id);
 }
@@ -466,7 +466,7 @@ static auto CheckBaseType(Context& context, Parse::NodeId node_id,
   auto base_type_id = ExprAsType(context, node_id, base_expr_id);
   base_type_id = context.AsCompleteType(base_type_id, [&] {
     CARBON_DIAGNOSTIC(IncompleteTypeInBaseDecl, Error,
-                      "Base `{0}` is an incomplete type.", SemIR::TypeId);
+                      "base `{0}` is an incomplete type", SemIR::TypeId);
     return context.emitter().Build(node_id, IncompleteTypeInBaseDecl,
                                    base_type_id);
   });
@@ -505,7 +505,7 @@ auto HandleParseNode(Context& context, Parse::BaseDeclId node_id) -> bool {
   LimitModifiersOnDecl(context, introducer, KeywordModifierSet::Extend);
   if (!introducer.modifier_set.HasAnyOf(KeywordModifierSet::Extend)) {
     CARBON_DIAGNOSTIC(BaseMissingExtend, Error,
-                      "Missing `extend` before `base` declaration in class.");
+                      "missing `extend` before `base` declaration");
     context.emitter().Emit(node_id, BaseMissingExtend);
   }
 
@@ -570,23 +570,23 @@ static auto CheckCompleteAdapterClassType(Context& context,
     -> SemIR::InstId {
   const auto& class_info = context.classes().Get(class_id);
   if (class_info.base_id.is_valid()) {
-    CARBON_DIAGNOSTIC(AdaptWithBase, Error,
-                      "Adapter cannot have a base class.");
-    CARBON_DIAGNOSTIC(AdaptBaseHere, Note, "`base` declaration is here.");
+    CARBON_DIAGNOSTIC(AdaptWithBase, Error, "adapter with base class");
+    CARBON_DIAGNOSTIC(AdaptWithBaseHere, Note, "`base` declaration is here");
     context.emitter()
         .Build(class_info.adapt_id, AdaptWithBase)
-        .Note(class_info.base_id, AdaptBaseHere)
+        .Note(class_info.base_id, AdaptWithBaseHere)
         .Emit();
     return SemIR::InstId::BuiltinError;
   }
 
   if (!context.inst_blocks().Get(fields_id).empty()) {
     auto first_field_id = context.inst_blocks().Get(fields_id).front();
-    CARBON_DIAGNOSTIC(AdaptWithFields, Error, "Adapter cannot have fields.");
-    CARBON_DIAGNOSTIC(AdaptFieldHere, Note, "First field declaration is here.");
+    CARBON_DIAGNOSTIC(AdaptWithFields, Error, "adapter with fields");
+    CARBON_DIAGNOSTIC(AdaptWithFieldHere, Note,
+                      "first field declaration is here");
     context.emitter()
         .Build(class_info.adapt_id, AdaptWithFields)
-        .Note(first_field_id, AdaptFieldHere)
+        .Note(first_field_id, AdaptWithFieldHere)
         .Emit();
     return SemIR::InstId::BuiltinError;
   }

toolchain/check/testdata/class/fail_adapt_bad_decl.carbon

@@ -53,10 +53,10 @@ library "[[@TEST_NAME]]";
 
 class MultipleAdapts {
   adapt ();
-  // CHECK:STDERR: fail_repeated.carbon:[[@LINE+7]]:3: error: Multiple `adapt` declarations in class.
+  // CHECK:STDERR: fail_repeated.carbon:[[@LINE+7]]:3: error: multiple `adapt` declarations in class
   // CHECK:STDERR:   adapt {};
   // CHECK:STDERR:   ^~~~~~~~~
-  // CHECK:STDERR: fail_repeated.carbon:[[@LINE-4]]:3: Previous `adapt` declaration is here.
+  // CHECK:STDERR: fail_repeated.carbon:[[@LINE-4]]:3: previous `adapt` declaration is here
   // CHECK:STDERR:   adapt ();
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR:
@@ -65,10 +65,10 @@ class MultipleAdapts {
 
 class MultipleAdaptsSameType {
   adapt ();
-  // CHECK:STDERR: fail_repeated.carbon:[[@LINE+7]]:3: error: Multiple `adapt` declarations in class.
+  // CHECK:STDERR: fail_repeated.carbon:[[@LINE+7]]:3: error: multiple `adapt` declarations in class
   // CHECK:STDERR:   adapt ();
   // CHECK:STDERR:   ^~~~~~~~~
-  // CHECK:STDERR: fail_repeated.carbon:[[@LINE-4]]:3: Previous `adapt` declaration is here.
+  // CHECK:STDERR: fail_repeated.carbon:[[@LINE-4]]:3: previous `adapt` declaration is here
   // CHECK:STDERR:   adapt ();
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR:
@@ -79,14 +79,14 @@ class MultipleAdaptsSameType {
 
 library "[[@TEST_NAME]]";
 
-// CHECK:STDERR: fail_bad_scope.carbon:[[@LINE+4]]:1: error: `adapt` declaration can only be used in a class.
+// CHECK:STDERR: fail_bad_scope.carbon:[[@LINE+4]]:1: error: `adapt` declaration outside class
 // CHECK:STDERR: adapt {};
 // CHECK:STDERR: ^~~~~~~~~
 // CHECK:STDERR:
 adapt {};
 
 interface I {
-  // CHECK:STDERR: fail_bad_scope.carbon:[[@LINE+4]]:3: error: `adapt` declaration can only be used in a class.
+  // CHECK:STDERR: fail_bad_scope.carbon:[[@LINE+4]]:3: error: `adapt` declaration outside class
   // CHECK:STDERR:   adapt {};
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR:
@@ -95,7 +95,7 @@ interface I {
 
 class C {
   interface I {
-    // CHECK:STDERR: fail_bad_scope.carbon:[[@LINE+3]]:5: error: `adapt` declaration can only be used in a class.
+    // CHECK:STDERR: fail_bad_scope.carbon:[[@LINE+3]]:5: error: `adapt` declaration outside class
     // CHECK:STDERR:     adapt {};
     // CHECK:STDERR:     ^~~~~~~~~
     adapt {};

toolchain/check/testdata/class/fail_adapt_bad_type.carbon

@@ -15,7 +15,7 @@ library "[[@TEST_NAME]]";
 class Incomplete;
 
 class AdaptIncomplete {
-  // CHECK:STDERR: fail_incomplete_type.carbon:[[@LINE+6]]:3: error: Adapted type `Incomplete` is an incomplete type.
+  // CHECK:STDERR: fail_incomplete_type.carbon:[[@LINE+6]]:3: error: adapted type `Incomplete` is an incomplete type
   // CHECK:STDERR:   adapt Incomplete;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~
   // CHECK:STDERR: fail_incomplete_type.carbon:[[@LINE-6]]:1: class was forward declared here

toolchain/check/testdata/class/fail_adapt_with_subobjects.carbon

@@ -15,11 +15,11 @@ library "[[@TEST_NAME]]";
 base class Base {}
 
 class AdaptWithBase {
-  // CHECK:STDERR: fail_adapt_with_base.carbon:[[@LINE+3]]:3: error: Adapter cannot have a base class.
+  // CHECK:STDERR: fail_adapt_with_base.carbon:[[@LINE+3]]:3: error: adapter with base class
   // CHECK:STDERR:   adapt i32;
   // CHECK:STDERR:   ^~~~~~~~~~
   adapt i32;
-  // CHECK:STDERR: fail_adapt_with_base.carbon:[[@LINE+4]]:3: `base` declaration is here.
+  // CHECK:STDERR: fail_adapt_with_base.carbon:[[@LINE+4]]:3: `base` declaration is here
   // CHECK:STDERR:   extend base: Base;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~
   // CHECK:STDERR:
@@ -31,11 +31,11 @@ class AdaptWithBase {
 library "[[@TEST_NAME]]";
 
 class AdaptWithField {
-  // CHECK:STDERR: fail_adapt_with_fields.carbon:[[@LINE+3]]:3: error: Adapter cannot have fields.
+  // CHECK:STDERR: fail_adapt_with_fields.carbon:[[@LINE+3]]:3: error: adapter with fields
   // CHECK:STDERR:   adapt i32;
   // CHECK:STDERR:   ^~~~~~~~~~
   adapt i32;
-  // CHECK:STDERR: fail_adapt_with_fields.carbon:[[@LINE+4]]:7: First field declaration is here.
+  // CHECK:STDERR: fail_adapt_with_fields.carbon:[[@LINE+4]]:7: first field declaration is here
   // CHECK:STDERR:   var n: i32;
   // CHECK:STDERR:       ^~~~~~
   // CHECK:STDERR:
@@ -43,11 +43,11 @@ class AdaptWithField {
 }
 
 class AdaptWithFields {
-  // CHECK:STDERR: fail_adapt_with_fields.carbon:[[@LINE+3]]:3: error: Adapter cannot have fields.
+  // CHECK:STDERR: fail_adapt_with_fields.carbon:[[@LINE+3]]:3: error: adapter with fields
   // CHECK:STDERR:   adapt i32;
   // CHECK:STDERR:   ^~~~~~~~~~
   adapt i32;
-  // CHECK:STDERR: fail_adapt_with_fields.carbon:[[@LINE+4]]:7: First field declaration is here.
+  // CHECK:STDERR: fail_adapt_with_fields.carbon:[[@LINE+4]]:7: first field declaration is here
   // CHECK:STDERR:   var a: i32;
   // CHECK:STDERR:       ^~~~~~
   // CHECK:STDERR:
@@ -65,10 +65,10 @@ base class Base {}
 class AdaptWithBaseAndFields {
   extend base: Base;
   var n: i32;
-  // CHECK:STDERR: fail_adapt_with_base_and_fields.carbon:[[@LINE+6]]:3: error: Adapter cannot have a base class.
+  // CHECK:STDERR: fail_adapt_with_base_and_fields.carbon:[[@LINE+6]]:3: error: adapter with base class
   // CHECK:STDERR:   adapt {};
   // CHECK:STDERR:   ^~~~~~~~~
-  // CHECK:STDERR: fail_adapt_with_base_and_fields.carbon:[[@LINE-5]]:3: `base` declaration is here.
+  // CHECK:STDERR: fail_adapt_with_base_and_fields.carbon:[[@LINE-5]]:3: `base` declaration is here
   // CHECK:STDERR:   extend base: Base;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~
   adapt {};

toolchain/check/testdata/class/fail_base_bad_type.carbon

@@ -38,7 +38,7 @@ class DeriveFromNonType {
 fn AccessMemberWithInvalidBasNonType(p: DeriveFromNonType*) -> i32 { return (*p).n; }
 
 class DeriveFromi32 {
-  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+4]]:16: error: Deriving from final type `i32`. Base type must be an `abstract` or `base` class.
+  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+4]]:16: error: deriving from final type `i32`; base type must be an `abstract` or `base` class
   // CHECK:STDERR:   extend base: i32;
   // CHECK:STDERR:                ^~~
   // CHECK:STDERR:
@@ -59,7 +59,7 @@ fn ConvertToBadBasei32(p: DeriveFromi32*) -> i32* { return p; }
 fn AccessMemberWithInvalidBasei32(p: DeriveFromi32*) -> i32 { return (*p).n; }
 
 class DeriveFromTuple {
-  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+4]]:16: error: Deriving from final type `(Base,)`. Base type must be an `abstract` or `base` class.
+  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+4]]:16: error: deriving from final type `(Base,)`; base type must be an `abstract` or `base` class
   // CHECK:STDERR:   extend base: (Base,);
   // CHECK:STDERR:                ^~~~~~~
   // CHECK:STDERR:
@@ -80,7 +80,7 @@ fn AccessMemberWithInvalidBaseTuple(p: DeriveFromTuple*) -> i32 { return (*p).n;
 // TODO: Should we allow this?
 // We do allow `{.base = {.a: i32, .b: i32}}`.
 class DeriveFromStruct {
-  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+4]]:16: error: Deriving from final type `{.a: i32, .b: i32}`. Base type must be an `abstract` or `base` class.
+  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+4]]:16: error: deriving from final type `{.a: i32, .b: i32}`; base type must be an `abstract` or `base` class
   // CHECK:STDERR:   extend base: {.a: i32, .b: i32};
   // CHECK:STDERR:                ^~~~~~~~~~~~~~~~~~
   // CHECK:STDERR:
@@ -102,7 +102,7 @@ fn AccessMemberWithInvalidBaseStruct(p: DeriveFromStruct*) -> i32 { return (*p).
 base class Incomplete;
 
 class DeriveFromIncomplete {
-  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+7]]:16: error: Base `Incomplete` is an incomplete type.
+  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+7]]:16: error: base `Incomplete` is an incomplete type
   // CHECK:STDERR:   extend base: Incomplete;
   // CHECK:STDERR:                ^~~~~~~~~~
   // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE-6]]:1: class was forward declared here
@@ -124,7 +124,7 @@ fn ConvertToBadBaseIncomplete(p: DeriveFromIncomplete*) -> Incomplete* { return
 fn AccessMemberWithInvalidBaseIncomplete(p: DeriveFromIncomplete*) -> i32 { return (*p).n; }
 
 class DeriveFromFinal {
-  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+4]]:16: error: Deriving from final type `Final`. Base type must be an `abstract` or `base` class.
+  // CHECK:STDERR: fail_base_bad_type.carbon:[[@LINE+4]]:16: error: deriving from final type `Final`; base type must be an `abstract` or `base` class
   // CHECK:STDERR:   extend base: Final;
   // CHECK:STDERR:                ^~~~~
   // CHECK:STDERR:

toolchain/check/testdata/class/fail_base_misplaced.carbon

@@ -10,7 +10,7 @@
 
 base class B {}
 
-// CHECK:STDERR: fail_base_misplaced.carbon:[[@LINE+4]]:1: error: `base` declaration can only be used in a class.
+// CHECK:STDERR: fail_base_misplaced.carbon:[[@LINE+4]]:1: error: `base` declaration outside class
 // CHECK:STDERR: extend base: B;
 // CHECK:STDERR: ^~~~~~~~~~~~~~~
 // CHECK:STDERR:

toolchain/check/testdata/class/fail_base_modifiers.carbon

@@ -23,7 +23,7 @@ class C2 {
   // CHECK:STDERR:   abstract base: B;
   // CHECK:STDERR:   ^~~~~~~~
   // CHECK:STDERR:
-  // CHECK:STDERR: fail_base_modifiers.carbon:[[@LINE+4]]:3: error: Missing `extend` before `base` declaration in class.
+  // CHECK:STDERR: fail_base_modifiers.carbon:[[@LINE+4]]:3: error: missing `extend` before `base` declaration
   // CHECK:STDERR:   abstract base: B;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~
   // CHECK:STDERR:

toolchain/check/testdata/class/fail_base_no_extend.carbon

@@ -11,7 +11,7 @@
 base class B {}
 
 class C {
-  // CHECK:STDERR: fail_base_no_extend.carbon:[[@LINE+3]]:3: error: Missing `extend` before `base` declaration in class.
+  // CHECK:STDERR: fail_base_no_extend.carbon:[[@LINE+3]]:3: error: missing `extend` before `base` declaration
   // CHECK:STDERR:   base: B;
   // CHECK:STDERR:   ^~~~~~~~
   base: B;

toolchain/check/testdata/class/fail_base_repeated.carbon

@@ -13,10 +13,10 @@ base class B2 {}
 
 class C {
   extend base: B1;
-  // CHECK:STDERR: fail_base_repeated.carbon:[[@LINE+7]]:3: error: Multiple `base` declarations in class. Multiple inheritance is not permitted.
+  // CHECK:STDERR: fail_base_repeated.carbon:[[@LINE+7]]:3: error: multiple `base` declarations in class; multiple inheritance is not permitted
   // CHECK:STDERR:   extend base: B2;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
-  // CHECK:STDERR: fail_base_repeated.carbon:[[@LINE-4]]:3: Previous `base` declaration is here.
+  // CHECK:STDERR: fail_base_repeated.carbon:[[@LINE-4]]:3: previous `base` declaration is here
   // CHECK:STDERR:   extend base: B1;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
   // CHECK:STDERR:
@@ -26,10 +26,10 @@ class C {
 class D {
   // TODO: Consider adding a custom diagnostic for this case.
   extend base: B1;
-  // CHECK:STDERR: fail_base_repeated.carbon:[[@LINE+6]]:3: error: Multiple `base` declarations in class. Multiple inheritance is not permitted.
+  // CHECK:STDERR: fail_base_repeated.carbon:[[@LINE+6]]:3: error: multiple `base` declarations in class; multiple inheritance is not permitted
   // CHECK:STDERR:   extend base: B1;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
-  // CHECK:STDERR: fail_base_repeated.carbon:[[@LINE-4]]:3: Previous `base` declaration is here.
+  // CHECK:STDERR: fail_base_repeated.carbon:[[@LINE-4]]:3: previous `base` declaration is here
   // CHECK:STDERR:   extend base: B1;
   // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
   extend base: B1;

toolchain/check/testdata/class/fail_redeclaration_introducer.carbon

@@ -13,10 +13,10 @@
 library "[[@TEST_NAME]]";
 
 class A;
-// CHECK:STDERR: fail_add_base.carbon:[[@LINE+7]]:1: error: Class redeclared with different inheritance kind.
+// CHECK:STDERR: fail_add_base.carbon:[[@LINE+7]]:1: error: class redeclared with different inheritance kind
 // CHECK:STDERR: base class A {}
 // CHECK:STDERR: ^~~~~~~~~~~~~~
-// CHECK:STDERR: fail_add_base.carbon:[[@LINE-4]]:1: Previously declared here.
+// CHECK:STDERR: fail_add_base.carbon:[[@LINE-4]]:1: previously declared here
 // CHECK:STDERR: class A;
 // CHECK:STDERR: ^~~~~~~~
 // CHECK:STDERR:
@@ -27,10 +27,10 @@ base class A {}
 library "[[@TEST_NAME]]";
 
 class B;
-// CHECK:STDERR: fail_add_abstract.carbon:[[@LINE+7]]:1: error: Class redeclared with different inheritance kind.
+// CHECK:STDERR: fail_add_abstract.carbon:[[@LINE+7]]:1: error: class redeclared with different inheritance kind
 // CHECK:STDERR: abstract class B {}
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
-// CHECK:STDERR: fail_add_abstract.carbon:[[@LINE-4]]:1: Previously declared here.
+// CHECK:STDERR: fail_add_abstract.carbon:[[@LINE-4]]:1: previously declared here
 // CHECK:STDERR: class B;
 // CHECK:STDERR: ^~~~~~~~
 // CHECK:STDERR:
@@ -41,10 +41,10 @@ abstract class B {}
 library "[[@TEST_NAME]]";
 
 base class C;
-// CHECK:STDERR: fail_remove_base.carbon:[[@LINE+7]]:1: error: Class redeclared with different inheritance kind.
+// CHECK:STDERR: fail_remove_base.carbon:[[@LINE+7]]:1: error: class redeclared with different inheritance kind
 // CHECK:STDERR: class C {}
 // CHECK:STDERR: ^~~~~~~~~
-// CHECK:STDERR: fail_remove_base.carbon:[[@LINE-4]]:1: Previously declared here.
+// CHECK:STDERR: fail_remove_base.carbon:[[@LINE-4]]:1: previously declared here
 // CHECK:STDERR: base class C;
 // CHECK:STDERR: ^~~~~~~~~~~~~
 // CHECK:STDERR:
@@ -55,10 +55,10 @@ class C {}
 library "[[@TEST_NAME]]";
 
 base class D;
-// CHECK:STDERR: fail_base_to_abstract.carbon:[[@LINE+7]]:1: error: Class redeclared with different inheritance kind.
+// CHECK:STDERR: fail_base_to_abstract.carbon:[[@LINE+7]]:1: error: class redeclared with different inheritance kind
 // CHECK:STDERR: abstract class D {}
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~~
-// CHECK:STDERR: fail_base_to_abstract.carbon:[[@LINE-4]]:1: Previously declared here.
+// CHECK:STDERR: fail_base_to_abstract.carbon:[[@LINE-4]]:1: previously declared here
 // CHECK:STDERR: base class D;
 // CHECK:STDERR: ^~~~~~~~~~~~~
 // CHECK:STDERR:
@@ -69,10 +69,10 @@ abstract class D {}
 library "[[@TEST_NAME]]";
 
 abstract class E;
-// CHECK:STDERR: fail_remove_abstract.carbon:[[@LINE+7]]:1: error: Class redeclared with different inheritance kind.
+// CHECK:STDERR: fail_remove_abstract.carbon:[[@LINE+7]]:1: error: class redeclared with different inheritance kind
 // CHECK:STDERR: class E {}
 // CHECK:STDERR: ^~~~~~~~~
-// CHECK:STDERR: fail_remove_abstract.carbon:[[@LINE-4]]:1: Previously declared here.
+// CHECK:STDERR: fail_remove_abstract.carbon:[[@LINE-4]]:1: previously declared here
 // CHECK:STDERR: abstract class E;
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~
 // CHECK:STDERR:
@@ -83,10 +83,10 @@ class E {}
 library "[[@TEST_NAME]]";
 
 abstract class F;
-// CHECK:STDERR: fail_abstract_to_base.carbon:[[@LINE+6]]:1: error: Class redeclared with different inheritance kind.
+// CHECK:STDERR: fail_abstract_to_base.carbon:[[@LINE+6]]:1: error: class redeclared with different inheritance kind
 // CHECK:STDERR: base class F {}
 // CHECK:STDERR: ^~~~~~~~~~~~~~
-// CHECK:STDERR: fail_abstract_to_base.carbon:[[@LINE-4]]:1: Previously declared here.
+// CHECK:STDERR: fail_abstract_to_base.carbon:[[@LINE-4]]:1: previously declared here
 // CHECK:STDERR: abstract class F;
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~~
 base class F {}

toolchain/diagnostics/diagnostic_kind.def

@@ -202,10 +202,12 @@ CARBON_DIAGNOSTIC_KIND(UnknownBuiltinFunctionName)
 CARBON_DIAGNOSTIC_KIND(InvalidBuiltinSignature)
 
 // Class checking.
+CARBON_DIAGNOSTIC_KIND(AdaptDeclRepeated)
 CARBON_DIAGNOSTIC_KIND(AdaptWithBase)
 CARBON_DIAGNOSTIC_KIND(AdaptWithFields)
-CARBON_DIAGNOSTIC_KIND(AdaptBaseHere)
-CARBON_DIAGNOSTIC_KIND(AdaptFieldHere)
+CARBON_DIAGNOSTIC_KIND(AdaptWithBaseHere)
+CARBON_DIAGNOSTIC_KIND(AdaptWithFieldHere)
+CARBON_DIAGNOSTIC_KIND(BaseDeclRepeated)
 CARBON_DIAGNOSTIC_KIND(BaseIsFinal)
 CARBON_DIAGNOSTIC_KIND(BaseMissingExtend)
 CARBON_DIAGNOSTIC_KIND(ClassForwardDeclaredHere)
@@ -213,7 +215,6 @@ CARBON_DIAGNOSTIC_KIND(ClassRedeclarationDifferentIntroducer)
 CARBON_DIAGNOSTIC_KIND(ClassRedeclarationDifferentIntroducerPrevious)
 CARBON_DIAGNOSTIC_KIND(ClassSpecificDeclOutsideClass)
 CARBON_DIAGNOSTIC_KIND(ClassSpecificDeclPrevious)
-CARBON_DIAGNOSTIC_KIND(ClassSpecificDeclRepeated)
 CARBON_DIAGNOSTIC_KIND(ClassIncompleteWithinDefinition)
 CARBON_DIAGNOSTIC_KIND(ConstructionOfAbstractClass)