On invalid parse nodes, if the token may vary, allow any token. (#3484)

Note #3486 rewrites the macro behavior, and is already approved: so this
PR is only for the changed enforcement during error. Also, #3493 already
changed several things to allow any token while this PR was awaiting
review, but this still changes enforcement for `For` and `If`.

This was brought up on
[#toolchain](https://discord.com/channels/655572317891461132/655578254970716160/1182066616456970251),
and I think this any-on-error approach gets at least some support. We
could try setting it to the introducer, but it's quite possible we want
it to be something like the token which led to the parse error, rather
than a static token. That leads to a conclusion that, most typically,
we'll expect arbitrary tokens when error conditions may lead to tokens
which aren't the expected token.

A couple related, recent `CARBON_IF_ERROR` crash fixes can be found in
#3404 and #3424. Something like #3404 would've been needed regardless
because `namespace` didn't have `CARBON_IF_ERROR` before, although I
might've missed the underlying issue with declarations because only
`namespace` had a relevant test (that is, if #3404 had added
`CARBON_ANY_TOKEN_ON_ERROR`, I wouldn't have had a crash in #3462).
#3424 would've been avoided with this change because there was a
`CARBON_IF_ERROR`, and it was just too restrictive.

toolchain/parse/node_kind.cpp

@@ -50,6 +50,11 @@ auto NodeKind::child_count() const -> int32_t {
 // NOLINTNEXTLINE(readability-function-size): It's hard to extract macros.
 auto CheckNodeMatchesLexerToken(NodeKind node_kind, Lex::TokenKind token_kind,
                                 bool has_error) -> void {
+  // As a special-case, a placeholder node may correspond to any lexer token.
+  if (node_kind == NodeKind::Placeholder) {
+    return;
+  }
+
   switch (node_kind) {
     // Use `CARBON_LOG CARBON_ANY_TOKEN` to discover which combinations happen
     // in practice.
@@ -58,16 +63,14 @@ auto CheckNodeMatchesLexerToken(NodeKind node_kind, Lex::TokenKind token_kind,
                << " and has_error " << has_error << " for lexical token " \
                << token_kind << "\n";
 
-#define CARBON_ANY_TOKEN return;
-
 #define CARBON_TOKEN(Expected)                  \
   if (token_kind == Lex::TokenKind::Expected) { \
     return;                                     \
   }
 
-#define CARBON_IF_ERROR(MatchActions) \
-  if (has_error) {                    \
-    MatchActions                      \
+#define CARBON_ANY_TOKEN_ON_ERROR \
+  if (has_error) {                \
+    return;                       \
   }
 
 #define CARBON_CASE(Name, MatchActions)                    \

toolchain/parse/node_kind.def

@@ -31,9 +31,8 @@
 //   In both cases, LexTokenKinds says which Lex::TokenKind values that this
 //   parse node can correspond to, and is a sequence of:
 //   - CARBON_TOKEN(kind): This node can correspond to this kind of token.
-//   - CARBON_ANY_TOKEN: This node can correspond to any token.
-//   - CARBON_IF_ERROR(LexTokenKinds): This node can additionally correspond
-//     to the given kinds of tokens if its `has_error` flag is set.
+//   - CARBON_ANY_TOKEN_ON_ERROR: When the `has_error` flag is set, this node
+//     can correspond to any token.
 //
 // This tree represents the subset relationship between these macros, where if a
 // specific x-macro isn't defined, it'll fall back to the parent macro.
@@ -64,8 +63,7 @@
 //   #define CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Name, ...) <code>
 #ifndef CARBON_PARSE_NODE_KIND_INFIX_OPERATOR
 #define CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Name) \
-  CARBON_PARSE_NODE_KIND_CHILD_COUNT(InfixOperator##Name, 2, \
-                                     CARBON_TOKEN(Name))
+  CARBON_PARSE_NODE_KIND_CHILD_COUNT(InfixOperator##Name, 2, CARBON_TOKEN(Name))
 #endif
 
 // This is expected to be used with something like:
@@ -74,7 +72,7 @@
 //   #define CARBON_PARSE_NODE_KIND(...)
 //   #define CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Name, ...) <code>
 #ifndef CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR
-#define CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Name) \
+#define CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Name)          \
   CARBON_PARSE_NODE_KIND_CHILD_COUNT(PrefixOperator##Name, 1, \
                                      CARBON_TOKEN(Name))
 #endif
@@ -106,27 +104,26 @@ CARBON_PARSE_NODE_KIND_CHILD_COUNT(FileStart, 0, CARBON_TOKEN(FileStart))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(FileEnd, 0, CARBON_TOKEN(FileEnd))
 
 // An invalid parse. Used to balance the parse tree. Always has an error.
-CARBON_PARSE_NODE_KIND_CHILD_COUNT(InvalidParse, 0,
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+CARBON_PARSE_NODE_KIND_CHILD_COUNT(InvalidParse, 0, CARBON_ANY_TOKEN_ON_ERROR)
 
 // An invalid subtree. Always has an error.
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(InvalidParseStart, 0,
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                   CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_BRACKET(InvalidParseSubtree, InvalidParseStart,
-                               CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_ANY_TOKEN_ON_ERROR)
 
-// A placeholder node to be replaced.
-CARBON_PARSE_NODE_KIND_CHILD_COUNT(Placeholder, 0, CARBON_ANY_TOKEN)
+// A placeholder node to be replaced. Its token kind is not enforced even when
+// valid, as a special-case in node_kind.cpp.
+CARBON_PARSE_NODE_KIND_CHILD_COUNT(Placeholder, 0, CARBON_ANY_TOKEN_ON_ERROR)
 
 // An empty declaration, such as `;`.
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(EmptyDecl, 0,
-                                   CARBON_TOKEN(Semi)
-                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                   CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // An identifier name in a non-expression context, such as a declaration.
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(IdentifierName, 0,
                                    CARBON_TOKEN(Identifier)
-                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                       CARBON_ANY_TOKEN_ON_ERROR)
 
 // An identifier name in an expression context.
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(IdentifierNameExpr, 0,
@@ -190,8 +187,7 @@ CARBON_PARSE_NODE_KIND_CHILD_COUNT(PackageIntroducer, 0, CARBON_TOKEN(Package))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(PackageApi, 0, CARBON_TOKEN(Api))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(PackageImpl, 0, CARBON_TOKEN(Impl))
 CARBON_PARSE_NODE_KIND_BRACKET(PackageDirective, PackageIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `import`:
 //   ImportIntroducer
@@ -200,8 +196,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(PackageDirective, PackageIntroducer,
 // ImportDirective
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ImportIntroducer, 0, CARBON_TOKEN(Import))
 CARBON_PARSE_NODE_KIND_BRACKET(ImportDirective, ImportIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 // `library` as directive:
 //   LibraryIntroducer
 //   DefaultLibrary or _external_: LibraryName
@@ -209,8 +204,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(ImportDirective, ImportIntroducer,
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(DefaultLibrary, 0, CARBON_TOKEN(Default))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(LibraryIntroducer, 0, CARBON_TOKEN(Library))
 CARBON_PARSE_NODE_KIND_BRACKET(LibraryDirective, LibraryIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `library` in `package` or `import`:
 //   _external_: LibraryName
@@ -224,8 +218,7 @@ CARBON_PARSE_NODE_KIND_CHILD_COUNT(LibrarySpecifier, 1, CARBON_TOKEN(Library))
 // Namespace
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(NamespaceStart, 0, CARBON_TOKEN(Namespace))
 CARBON_PARSE_NODE_KIND_BRACKET(Namespace, NamespaceStart,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // A code block:
 //   CodeBlockStart
@@ -233,10 +226,10 @@ CARBON_PARSE_NODE_KIND_BRACKET(Namespace, NamespaceStart,
 // CodeBlock
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(CodeBlockStart, 0,
                                    CARBON_TOKEN(OpenCurlyBrace)
-                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                       CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_BRACKET(CodeBlock, CodeBlockStart,
                                CARBON_TOKEN(CloseCurlyBrace)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                   CARBON_ANY_TOKEN_ON_ERROR)
 
 // `fn`:
 //     FunctionIntroducer
@@ -259,8 +252,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(FunctionDefinitionStart, FunctionIntroducer,
 CARBON_PARSE_NODE_KIND_BRACKET(FunctionDefinition, FunctionDefinitionStart,
                                CARBON_TOKEN(CloseCurlyBrace))
 CARBON_PARSE_NODE_KIND_BRACKET(FunctionDecl, FunctionIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // A tuple pattern:
 //   TuplePatternStart
@@ -288,8 +280,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(TuplePattern, TuplePatternStart,
 // separator.
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ImplicitParamListStart, 0,
                                    CARBON_TOKEN(OpenSquareBracket))
-CARBON_PARSE_NODE_KIND_BRACKET(ImplicitParamList,
-                               ImplicitParamListStart,
+CARBON_PARSE_NODE_KIND_BRACKET(ImplicitParamList, ImplicitParamListStart,
                                CARBON_TOKEN(CloseSquareBracket))
 
 // An array type, such as  `[i32; 3]` or `[i32;]`:
@@ -301,8 +292,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(ImplicitParamList,
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ArrayExprStart, 0,
                                    CARBON_TOKEN(OpenSquareBracket))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ArrayExprSemi, 2,
-                                   CARBON_TOKEN(Semi)
-                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                   CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_BRACKET(ArrayExpr, ArrayExprSemi,
                                CARBON_TOKEN(CloseSquareBracket))
 
@@ -314,7 +304,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(ArrayExpr, ArrayExprSemi,
 // _optional_ Template
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(BindingPattern, 2,
                                    CARBON_TOKEN(Colon)
-                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                       CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(GenericBindingPattern, 2,
                                    CARBON_TOKEN(ColonExclaim))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(Address, 1, CARBON_TOKEN(Addr))
@@ -332,8 +322,7 @@ CARBON_PARSE_NODE_KIND_CHILD_COUNT(Template, 1, CARBON_TOKEN(Template))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(LetIntroducer, 0, CARBON_TOKEN(Let))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(LetInitializer, 0, CARBON_TOKEN(Equal))
 CARBON_PARSE_NODE_KIND_BRACKET(LetDecl, LetIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `var` and `returned var`:
 //   VariableIntroducer
@@ -350,28 +339,24 @@ CARBON_PARSE_NODE_KIND_BRACKET(LetDecl, LetIntroducer,
 // The VariableInitializer and following expression are paired: either both will
 // be present, or neither will.
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(VariableIntroducer, 0,
-                                   CARBON_TOKEN(Var)
-                                       CARBON_IF_ERROR(CARBON_TOKEN(Returned)))
+                                   CARBON_TOKEN(Var) CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ReturnedModifier, 0, CARBON_TOKEN(Returned))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(VariableInitializer, 0, CARBON_TOKEN(Equal))
 CARBON_PARSE_NODE_KIND_BRACKET(VariableDecl, VariableIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // An expression statement:
 //   _external_: expression
 // ExprStatement
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ExprStatement, 1,
-                                   CARBON_TOKEN(Semi)
-                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                   CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `break`:
 //   BreakStatementStart
 // BreakStatement
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(BreakStatementStart, 0, CARBON_TOKEN(Break))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(BreakStatement, 1,
-                                   CARBON_TOKEN(Semi)
-                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                   CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `continue`:
 //   ContinueStatementStart
@@ -379,8 +364,7 @@ CARBON_PARSE_NODE_KIND_CHILD_COUNT(BreakStatement, 1,
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ContinueStatementStart, 0,
                                    CARBON_TOKEN(Continue))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ContinueStatement, 1,
-                                   CARBON_TOKEN(Semi)
-                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                                   CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `return`:
 //   ReturnStatementStart
@@ -390,8 +374,7 @@ CARBON_PARSE_NODE_KIND_CHILD_COUNT(ReturnStatementStart, 0,
                                    CARBON_TOKEN(Return))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ReturnVarModifier, 0, CARBON_TOKEN(Var))
 CARBON_PARSE_NODE_KIND_BRACKET(ReturnStatement, ReturnStatementStart,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `for`:
 //     ForHeaderStart
@@ -406,13 +389,12 @@ CARBON_PARSE_NODE_KIND_BRACKET(ReturnStatement, ReturnStatementStart,
 // Versus a normal `var`, ForIn replaces VariableDecl.
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ForHeaderStart, 0,
                                    CARBON_TOKEN(OpenParen)
-                                       CARBON_IF_ERROR(CARBON_TOKEN(For)))
+                                       CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_BRACKET(ForIn, VariableIntroducer,
-                               CARBON_TOKEN(In)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(In) CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_BRACKET(ForHeader, ForHeaderStart,
                                CARBON_TOKEN(CloseParen)
-                                   CARBON_IF_ERROR(CARBON_TOKEN(For)))
+                                   CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(ForStatement, 2, CARBON_TOKEN(For))
 
 // `if` statement + `else`:
@@ -427,10 +409,10 @@ CARBON_PARSE_NODE_KIND_CHILD_COUNT(ForStatement, 2, CARBON_TOKEN(For))
 // IfStatementElse and the following node are optional based on `else` presence.
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfConditionStart, 0,
                                    CARBON_TOKEN(OpenParen)
-                                       CARBON_IF_ERROR(CARBON_TOKEN(If)))
+                                       CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_BRACKET(IfCondition, IfConditionStart,
                                CARBON_TOKEN(CloseParen)
-                                   CARBON_IF_ERROR(CARBON_TOKEN(If)))
+                                   CARBON_ANY_TOKEN_ON_ERROR)
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfStatementElse, 0, CARBON_TOKEN(Else))
 CARBON_PARSE_NODE_KIND_BRACKET(IfStatement, IfCondition, CARBON_TOKEN(If))
 
@@ -470,8 +452,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(IndexExpr, IndexExprStart,
 //
 // Expressions and TupleLiteralComma may repeat with TupleLiteralComma as a
 // separator.
-CARBON_PARSE_NODE_KIND_CHILD_COUNT(ExprOpenParen, 0,
-                                   CARBON_TOKEN(OpenParen))
+CARBON_PARSE_NODE_KIND_CHILD_COUNT(ExprOpenParen, 0, CARBON_TOKEN(OpenParen))
 CARBON_PARSE_NODE_KIND_BRACKET(ParenExpr, ExprOpenParen,
                                CARBON_TOKEN(CloseParen))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(TupleLiteralComma, 0, CARBON_TOKEN(Comma))
@@ -611,8 +592,7 @@ CARBON_PARSE_NODE_KIND_CHILD_COUNT(PostfixOperatorStar, 1, CARBON_TOKEN(Star))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfExprIf, 1, CARBON_TOKEN(If))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfExprThen, 1, CARBON_TOKEN(Then))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfExprElse, 3,
-                                   CARBON_TOKEN(Else)
-                                       CARBON_IF_ERROR(CARBON_TOKEN(If)))
+                                   CARBON_TOKEN(Else) CARBON_ANY_TOKEN_ON_ERROR)
 
 // Struct literals, such as `{.a = 0}`:
 //   StructLiteralOrStructTypeLiteralStart
@@ -682,8 +662,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(ClassDefinitionStart, ClassIntroducer,
 CARBON_PARSE_NODE_KIND_BRACKET(ClassDefinition, ClassDefinitionStart,
                                CARBON_TOKEN(CloseCurlyBrace))
 CARBON_PARSE_NODE_KIND_BRACKET(ClassDecl, ClassIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `base`:
 //   BaseIntroducer
@@ -694,8 +673,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(ClassDecl, ClassIntroducer,
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(BaseIntroducer, 0, CARBON_TOKEN(Base))
 CARBON_PARSE_NODE_KIND_CHILD_COUNT(BaseColon, 0, CARBON_TOKEN(Colon))
 CARBON_PARSE_NODE_KIND_BRACKET(BaseDecl, BaseIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `interface`:
 //     InterfaceIntroducer
@@ -715,8 +693,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDefinitionStart, InterfaceIntroducer,
 CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDefinition, InterfaceDefinitionStart,
                                CARBON_TOKEN(CloseCurlyBrace))
 CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDecl, InterfaceIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `impl ... as`:
 //     ImplIntroducer
@@ -744,8 +721,7 @@ CARBON_PARSE_NODE_KIND_BRACKET(ImplDefinitionStart, ImplIntroducer,
 CARBON_PARSE_NODE_KIND_BRACKET(ImplDefinition, ImplDefinitionStart,
                                CARBON_TOKEN(CloseCurlyBrace))
 CARBON_PARSE_NODE_KIND_BRACKET(ImplDecl, ImplIntroducer,
-                               CARBON_TOKEN(Semi)
-                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
+                               CARBON_TOKEN(Semi) CARBON_ANY_TOKEN_ON_ERROR)
 
 // `constraint`:
 //     NamedConstraintIntroducer
@@ -777,5 +753,4 @@ CARBON_PARSE_NODE_KIND_BRACKET(NamedConstraintDecl, NamedConstraintIntroducer,
 #undef CARBON_PARSE_NODE_KIND_TOKEN_LITERAL
 #undef CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER
 #undef CARBON_TOKEN
-#undef CARBON_ANY_TOKEN
-#undef CARBON_IF_ERROR
+#undef CARBON_ANY_TOKEN_ON_ERROR

toolchain/parse/testdata/class/fail_modifiers.carbon

@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+virtual class B
+
+// CHECK:STDERR: fail_modifiers.carbon:[[@LINE+6]]:1: ERROR: `virtual` declarations must either end with a `;` or have a `{ ... }` block for a definition.
+// CHECK:STDERR: impl class
+// CHECK:STDERR: ^~~~
+// CHECK:STDERR: fail_modifiers.carbon:[[@LINE+3]]:6: ERROR: `class` introducer should be followed by a name.
+// CHECK:STDERR: impl class
+// CHECK:STDERR:      ^~~~~
+impl class
+
+// CHECK:STDOUT: - filename: fail_modifiers.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:       {kind: 'ClassIntroducer', text: 'class'},
+// CHECK:STDOUT:       {kind: 'VirtualModifier', text: 'virtual'},
+// CHECK:STDOUT:       {kind: 'IdentifierName', text: 'B'},
+// CHECK:STDOUT:     {kind: 'ClassDecl', text: 'impl', has_error: yes, subtree_size: 4},
+// CHECK:STDOUT:       {kind: 'ClassIntroducer', text: 'class'},
+// CHECK:STDOUT:       {kind: 'InvalidParse', text: '', has_error: yes},
+// CHECK:STDOUT:     {kind: 'ClassDecl', text: 'class', has_error: yes, subtree_size: 3},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]

toolchain/parse/testdata/namespace/fail_modifiers.carbon

@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+virtual namespace B
+
+// CHECK:STDERR: fail_modifiers.carbon:[[@LINE+6]]:1: ERROR: `namespace` declarations must end with a `;`.
+// CHECK:STDERR: impl namespace
+// CHECK:STDERR: ^~~~
+// CHECK:STDERR: fail_modifiers.carbon:[[@LINE+3]]:6: ERROR: `namespace` introducer should be followed by a name.
+// CHECK:STDERR: impl namespace
+// CHECK:STDERR:      ^~~~~~~~~
+impl namespace
+
+// CHECK:STDOUT: - filename: fail_modifiers.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:       {kind: 'NamespaceStart', text: 'namespace'},
+// CHECK:STDOUT:       {kind: 'VirtualModifier', text: 'virtual'},
+// CHECK:STDOUT:       {kind: 'IdentifierName', text: 'B'},
+// CHECK:STDOUT:     {kind: 'Namespace', text: 'impl', has_error: yes, subtree_size: 4},
+// CHECK:STDOUT:       {kind: 'NamespaceStart', text: 'namespace'},
+// CHECK:STDOUT:       {kind: 'InvalidParse', text: '', has_error: yes},
+// CHECK:STDOUT:     {kind: 'Namespace', text: 'namespace', has_error: yes, subtree_size: 3},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]