carbon-lang/toolchain/parse/node_kind.def

// 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
//
// This is an X-macro header. It does not use `#include` guards, and instead is
// designed to be `#include`ed after the x-macro is defined in order for its
// inclusion to expand to the desired output. Macro definitions are cleaned up
// at the end of this file.
//
// Supported x-macros are:
// - CARBON_PARSE_NODE_KIND(Name)
//   Used as a fallback if other macros are missing. No kinds should use this
//   directly.
//   - CARBON_PARSE_NODE_KIND_BRACKET(Name, BracketName, LexTokenKinds)
//     Defines a bracketed node kind. BracketName should refer to the node
//     kind that is the _start_ of the bracketed range.
//   - CARBON_PARSE_NODE_KIND_CHILD_COUNT(Name, ChildCount, LexTokenKinds)
//     Defines a parse node with a set number of children, often 0. This count
//     must be correct even when the node contains errors.
//   - CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(Name, TokenIndex)
//     Defines a parse node that corresponds to a token that is a single-token
//     literal. The token is wrapped for LexTokenKinds.
//
//   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.
//
// 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.
//
// Parse nodes are clustered based on language feature. Comments will show their
// relationship in postorder, using indentation for child node relationships.

#if !(defined(CARBON_PARSE_NODE_KIND) ||          \
      (defined(CARBON_PARSE_NODE_KIND_BRACKET) && \
       defined(CARBON_PARSE_NODE_KIND_CHILD_COUNT)))
#error "Must define CARBON_PARSE_NODE_KIND family x-macros to use this file."
#endif

// The BRACKET and CHILD_COUNT macros will use CARBON_PARSE_NODE_KIND by default
// when undefined.
#ifndef CARBON_PARSE_NODE_KIND_BRACKET
#define CARBON_PARSE_NODE_KIND_BRACKET(Name, ...) CARBON_PARSE_NODE_KIND(Name)
#endif
#ifndef CARBON_PARSE_NODE_KIND_CHILD_COUNT
#define CARBON_PARSE_NODE_KIND_CHILD_COUNT(Name, ...) \
  CARBON_PARSE_NODE_KIND(Name)
#endif

// This is expected to be used with something like:
//
//   // Use x-macros to handle literal cases.
//   #define CARBON_PARSE_NODE_KIND(...)
//   #define CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(Name, ...) <code>
#ifndef CARBON_PARSE_NODE_KIND_TOKEN_LITERAL
#define CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(Name, LexTokenKinds) \
  CARBON_PARSE_NODE_KIND_CHILD_COUNT(Name, 0, LexTokenKinds)
#endif

// The start of the file.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(FileStart, 0, CARBON_TOKEN(FileStart))

// The end of the file.
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))

// An invalid subtree. Always has an error.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(InvalidParseStart, 0,
                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
CARBON_PARSE_NODE_KIND_BRACKET(InvalidParseSubtree, InvalidParseStart,
                               CARBON_IF_ERROR(CARBON_ANY_TOKEN))

// A placeholder node to be replaced.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(Placeholder, 0, CARBON_ANY_TOKEN)

// An empty declaration, such as `;`.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(EmptyDecl, 0,
                                   CARBON_TOKEN(Semi)
                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))

// A name in a non-expression context, such as a declaration.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(Name, 0,
                                   CARBON_TOKEN(Identifier)
                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))

// A name in an expression context.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(NameExpr, 0, CARBON_TOKEN(Identifier))

// ----------------------------------------------------------------------------

// The comments below follow this pattern:
//
// // Descriptive heading:
// //   Child1
// //   Child2
// // Parent
//
// In this, `Child1`, `Child2`, and `Parent` are all kinds of parse nodes, which
// are then defined using the `CARBON_PARSE_NODE_KIND_*` macros. They are
// written in postorder, with the indentation showing the tree structure. See
// tree.h for more information.
//
// A parse node kind may be preceded by:
// -  `_optional_` if this node (or nodes) may be present or omitted in valid
//    parses, depending on which tokens are in the source code.
// -  `_repeated_` if this node (or nodes) may be repeated or omitted in valid
//    parses, depending on which tokens are in the source code.
// -  `_external_:` if this node is the child of multiple kinds of nodes and
//    is documented separately.
//
// There is generally a close correspondence between handling of tokens and the
// creation of non-external nodes in a given block.

// ----------------------------------------------------------------------------

// The name of a package or library for `package`, `import`, and `library`.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PackageName, 0, CARBON_TOKEN(Identifier))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(LibraryName, 0, CARBON_TOKEN(StringLiteral))

// `package`:
//   PackageIntroducer
//   _optional_ _external_: PackageName
//   _optional_ _external_: LibrarySpecifier
//   PackageApi or PackageImpl
// PackageDirective
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_TOKEN(Package)))

// `import`:
//   ImportIntroducer
//   _optional_ _external_: PackageName
//   _optional_ _external_: LibrarySpecifier
// 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_TOKEN(Import)))
// `library` as directive:
//   LibraryIntroducer
//   DefaultLibrary or _external_: LibraryName
// LibraryDirective
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_TOKEN(Library)))

// `library` in `package` or `import`:
//   _external_: LibraryName
// LibrarySpecifier
CARBON_PARSE_NODE_KIND_CHILD_COUNT(LibrarySpecifier, 1, CARBON_TOKEN(Library))

// `namespace`:
//   NamespaceStart
//   _external_: Name or QualifiedDecl
// Namespace
CARBON_PARSE_NODE_KIND_CHILD_COUNT(NamespaceStart, 0, CARBON_TOKEN(Namespace))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(Namespace, 2,
                                   CARBON_TOKEN(Semi)
                                       CARBON_IF_ERROR(CARBON_TOKEN(Namespace)))

// A code block:
//   CodeBlockStart
//   _repeated_ _external_: statement
// CodeBlock
CARBON_PARSE_NODE_KIND_CHILD_COUNT(CodeBlockStart, 0,
                                   CARBON_TOKEN(OpenCurlyBrace)
                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
CARBON_PARSE_NODE_KIND_BRACKET(CodeBlock, CodeBlockStart,
                               CARBON_TOKEN(CloseCurlyBrace)
                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))

// `fn`:
//     FunctionIntroducer
//     _repeated_ _external_: AccessModifierKeyword or DeclModifierKeyword
//     _external_: Name or QualifiedDecl
//     _external_: ParamList
//       _external_: type expression
//     ReturnType
//   FunctionDefinitionStart
//   _repeated_ _external_: statement
// FunctionDefinition
//
// The above is the structure for a definition; for a declaration,
// FunctionDefinitionStart and later nodes are removed and replaced by
// FunctionDecl.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(FunctionIntroducer, 0, CARBON_TOKEN(Fn))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ReturnType, 1, CARBON_TOKEN(MinusGreater))
CARBON_PARSE_NODE_KIND_BRACKET(FunctionDefinitionStart, FunctionIntroducer,
                               CARBON_TOKEN(OpenCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(FunctionDefinition, FunctionDefinitionStart,
                               CARBON_TOKEN(CloseCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(FunctionDecl, FunctionIntroducer,
                               CARBON_TOKEN(Semi)
                                   CARBON_IF_ERROR(CARBON_TOKEN(Fn)))

// A parameter list, possibly implicit:
//   [Implicit]ParamListStart
//     _external_: [Generic]BindingPattern
//     ParamListComma
//   _repeated_
// [Implicit]ParamList
//
// [Generic]PatternBinding and ParamListComma may repeat with ParamListComma
// as a separator.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ParamListStart, 0, CARBON_TOKEN(OpenParen))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ImplicitParamListStart, 0,
                                   CARBON_TOKEN(OpenSquareBracket))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ParamListComma, 0, CARBON_TOKEN(Comma))
CARBON_PARSE_NODE_KIND_BRACKET(ParamList, ParamListStart,
                               CARBON_TOKEN(CloseParen))
CARBON_PARSE_NODE_KIND_BRACKET(ImplicitParamList, ImplicitParamListStart,
                               CARBON_TOKEN(CloseSquareBracket))

// An array type, such as  `[i32; 3]` or `[i32;]`:
//     ArrayExprStart
//     _external_: type expression
//   ArrayExprSemi
//   _optional_ _external_: expression
// ArrayExpr
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_PARSE_NODE_KIND_BRACKET(ArrayExpr, ArrayExprSemi,
                               CARBON_TOKEN(CloseSquareBracket))

// A binding pattern, such as `name: Type`:
//       Name or SelfValueName
//       _external_: type expression
//     [Generic]BindingPattern
//   _optional_ Address
// _optional_ Template
CARBON_PARSE_NODE_KIND_CHILD_COUNT(BindingPattern, 2,
                                   CARBON_TOKEN(Colon)
                                       CARBON_IF_ERROR(CARBON_ANY_TOKEN))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(GenericBindingPattern, 2,
                                   CARBON_TOKEN(ColonExclaim))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(Address, 1, CARBON_TOKEN(Addr))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(Template, 1, CARBON_TOKEN(Template))

// `let`:
//   LetIntroducer
//   _repeated_ _external_: AccessModifierKeyword or DeclModifierKeyword
//   _external_: BindingPattern
//   LetInitializer
//   _external_: expression
// LetDecl
//
// Modifier keywords only appear for `let` declarations, not `let` statements.
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_TOKEN(Let)))

// `var` and `returned var`:
//   VariableIntroducer
//   _repeated_ _external_: AccessModifierKeyword or DeclModifierKeyword
//   _optional_ ReturnedModifier
//   _external_: BindingPattern
//     VariableInitializer
//     _external_: expression
//   _optional_
// VariableDecl
//
// Access and declaration modifier keywords only appear for `var` declarations,
// whereas the returned modifier only appears on `var` statements.
// 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_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_TOKEN(Var)
                                                       CARBON_TOKEN(Returned)))

// An expression statement:
//   _external_: expression
// ExprStatement
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ExprStatement, 1, CARBON_TOKEN(Semi))

// `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_TOKEN(Break)))

// `continue`:
//   ContinueStatementStart
// ContinueStatement
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_TOKEN(Continue)))

// `return`:
//   ReturnStatementStart
//   _optional_ ReturnVarModifier or _external_: expression
// ReturnStatement
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_TOKEN(Return)))

// `for`:
//     ForHeaderStart
//       VariableIntroducer
//       _external_: BindingPattern
//     ForIn
//     _external_: expression
//   ForHeader
//   _external_: CodeBlock
// ForStatement
//
// 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_PARSE_NODE_KIND_BRACKET(ForIn, VariableIntroducer,
                               CARBON_TOKEN(In)
                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
CARBON_PARSE_NODE_KIND_BRACKET(ForHeader, ForHeaderStart,
                               CARBON_TOKEN(CloseParen)
                                   CARBON_IF_ERROR(CARBON_TOKEN(For)))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ForStatement, 2, CARBON_TOKEN(For))

// `if` statement + `else`:
//     IfConditionStart
//     _external_: expression
//   IfCondition
//   _external_: CodeBlock
//   IfStatementElse
//   _external_: CodeBlock or IfStatement
// IfStatement
//
// 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_PARSE_NODE_KIND_BRACKET(IfCondition, IfConditionStart,
                               CARBON_TOKEN(CloseParen)
                                   CARBON_IF_ERROR(CARBON_TOKEN(If)))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfStatementElse, 0, CARBON_TOKEN(Else))
CARBON_PARSE_NODE_KIND_BRACKET(IfStatement, IfCondition, CARBON_TOKEN(If))

// `while`:
//     WhileConditionStart
//     _external_: expression
//   WhileCondition
//   _external_: CodeBlock
// WhileStatement
CARBON_PARSE_NODE_KIND_CHILD_COUNT(WhileConditionStart, 0,
                                   CARBON_TOKEN(OpenParen))
CARBON_PARSE_NODE_KIND_BRACKET(WhileCondition, WhileConditionStart,
                               CARBON_TOKEN(CloseParen))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(WhileStatement, 2, CARBON_TOKEN(While))

// Index expressions, such as `a[1]`:
//     _external_: expression
//   IndexExprStart
//   _external_: expression
// IndexExpr
CARBON_PARSE_NODE_KIND_CHILD_COUNT(IndexExprStart, 1,
                                   CARBON_TOKEN(OpenSquareBracket))
CARBON_PARSE_NODE_KIND_BRACKET(IndexExpr, IndexExprStart,
                               CARBON_TOKEN(CloseSquareBracket))

// Parenthesized expressions, such as `(2)`:
//   ParenExprOrTupleLiteralStart
//   _external_: expression
// ParenExpr
//
// Tuples, such as `(1, 2)`:
//   ParenExprOrTupleLiteralStart
//     _external_: expression
//     TupleLiteralComma
//   _repeated_
// TupleLiteral
//
// Expressions and TupleLiteralComma may repeat with TupleLiteralComma as a
// separator.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ParenExprOrTupleLiteralStart, 0,
                                   CARBON_TOKEN(OpenParen))
CARBON_PARSE_NODE_KIND_BRACKET(ParenExpr, ParenExprOrTupleLiteralStart,
                               CARBON_TOKEN(CloseParen))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(TupleLiteralComma, 0, CARBON_TOKEN(Comma))
CARBON_PARSE_NODE_KIND_BRACKET(TupleLiteral, ParenExprOrTupleLiteralStart,
                               CARBON_TOKEN(CloseParen))

// Call expressions, such as `a()`:
//     _external_: expression
//   CallExprStart
//     _external_: expression
//     CallExprComma
//   _repeated_
// CallExpr
//
// Exprs and CallExprComma may repeat with CallExprComma as a separator.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(CallExprStart, 1, CARBON_TOKEN(OpenParen))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(CallExprComma, 0, CARBON_TOKEN(Comma))
CARBON_PARSE_NODE_KIND_BRACKET(CallExpr, CallExprStart,
                               CARBON_TOKEN(CloseParen))

// A qualified declaration, such as `a.b`:
//   _external_: Name or QualifiedDecl
//   _external_: Name
// QualifiedDecl
//
// TODO: This will eventually more general expressions, for example with
// `GenericType(type_args).ChildType(child_type_args).Name`.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(QualifiedDecl, 2, CARBON_TOKEN(Period))

// A member access expression, such as `a.b` or
// `GetObject().(Interface.member)`:
//   _external_: lhs expression
//   _external_: rhs expression
// QualifiedExpr
CARBON_PARSE_NODE_KIND_CHILD_COUNT(MemberAccessExpr, 2, CARBON_TOKEN(Period))

// A pointer member access expression, such as `a->b` or
// `GetObject()->(Interface.member)`:
//   _external_: lhs expression
//   _external_: rhs expression
// QualifiedExpr
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PointerMemberAccessExpr, 2,
                                   CARBON_TOKEN(MinusGreater))

// A value literal.
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(BoolLiteralFalse, CARBON_TOKEN(False))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(BoolLiteralTrue, CARBON_TOKEN(True))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(IntLiteral,
                                     CARBON_TOKEN(IntLiteral))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(RealLiteral, CARBON_TOKEN(RealLiteral))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(StringLiteral, CARBON_TOKEN(StringLiteral))

// A type literal.
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(BoolTypeLiteral, CARBON_TOKEN(Bool))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(IntTypeLiteral,
                                     CARBON_TOKEN(IntTypeLiteral))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(UnsignedIntTypeLiteral,
                                     CARBON_TOKEN(UnsignedIntTypeLiteral))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(FloatTypeLiteral,
                                     CARBON_TOKEN(FloatTypeLiteral))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(StringTypeLiteral,
                                     CARBON_TOKEN(StringTypeLiteral))
CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(TypeTypeLiteral, CARBON_TOKEN(Type))

// clang-format off

// A prefix operator:
//   _external_: expression
// PrefixOperator
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PrefixOperator, 1,
                                   CARBON_TOKEN(Star)
                                   CARBON_TOKEN(Amp)
                                   CARBON_TOKEN(Not)
                                   CARBON_TOKEN(Minus)
                                   CARBON_TOKEN(MinusMinus)
                                   CARBON_TOKEN(PlusPlus)
                                   CARBON_TOKEN(Caret)
                                   CARBON_TOKEN(Const))

// An infix operator:
//   _external_: lhs expression
//   _external_: rhs expression
// InfixOperator
CARBON_PARSE_NODE_KIND_CHILD_COUNT(InfixOperator, 2,
                                   CARBON_TOKEN(Amp)
                                   CARBON_TOKEN(AmpEqual)
                                   CARBON_TOKEN(And)
                                   CARBON_TOKEN(As)
                                   CARBON_TOKEN(Caret)
                                   CARBON_TOKEN(CaretEqual)
                                   CARBON_TOKEN(Equal)
                                   CARBON_TOKEN(EqualEqual)
                                   CARBON_TOKEN(ExclaimEqual)
                                   CARBON_TOKEN(Greater)
                                   CARBON_TOKEN(GreaterEqual)
                                   CARBON_TOKEN(GreaterGreater)
                                   CARBON_TOKEN(GreaterGreaterEqual)
                                   CARBON_TOKEN(Less)
                                   CARBON_TOKEN(LessEqual)
                                   CARBON_TOKEN(LessLess)
                                   CARBON_TOKEN(LessLessEqual)
                                   CARBON_TOKEN(Minus)
                                   CARBON_TOKEN(MinusEqual)
                                   CARBON_TOKEN(Or)
                                   CARBON_TOKEN(Percent)
                                   CARBON_TOKEN(PercentEqual)
                                   CARBON_TOKEN(Pipe)
                                   CARBON_TOKEN(PipeEqual)
                                   CARBON_TOKEN(Plus)
                                   CARBON_TOKEN(PlusEqual)
                                   CARBON_TOKEN(Slash)
                                   CARBON_TOKEN(SlashEqual)
                                   CARBON_TOKEN(Star)
                                   CARBON_TOKEN(StarEqual))

// clang-format on

// The first operand of a short-circuiting infix operator:
//     _external_: expression
//   ShortCircuitOperand
//   _external_: expression
// _external_: InfixOperator
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ShortCircuitOperand, 1,
                                   CARBON_TOKEN(And) CARBON_TOKEN(Or))

// A postfix operator:
//   _external_: expression
// PostfixOperator
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PostfixOperator, 1, CARBON_TOKEN(Star))

// `if` expression + `then` + `else`:
//     _external_: expression
//   IfExprIf
//     _external_: expression
//   IfExprThen
//   _external_: expression
// IfExprElse
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)))

// Struct literals, such as `{.a = 0}`:
//   StructLiteralOrStructTypeLiteralStart
//         _external_: Name
//       StructFieldDesignator
//       _external_: expression
//     StructFieldValue
//     StructComma
//   _repeated_
// StructLiteral
//
// Struct type literals, such as `{.a: i32}`:
//   StructLiteralOrStructTypeLiteralStart
//         _external_: Name
//       StructFieldDesignator
//       _external_: type expression
//     StructFieldType
//     StructComma
//   _repeated_
// StructTypeLiteral
//
// Elements (StructFieldValue and StructFieldType, respectively) and StructComma
// may repeat with StructComma as a separator.
//
// When a valid StructFieldType or StructFieldValue cannot be formed, elements
// may be replaced by StructFieldUnknown, which may have a preceding sibling
// StructFieldDesignator if one was successfully parsed.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructLiteralOrStructTypeLiteralStart, 0,
                                   CARBON_TOKEN(OpenCurlyBrace))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructFieldDesignator, 1,
                                   CARBON_TOKEN(Period))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructFieldValue, 2, CARBON_TOKEN(Equal))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructFieldType, 2, CARBON_TOKEN(Colon))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructFieldUnknown, 0,
                                   CARBON_IF_ERROR(CARBON_ANY_TOKEN))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructComma, 0, CARBON_TOKEN(Comma))
CARBON_PARSE_NODE_KIND_BRACKET(StructLiteral,
                               StructLiteralOrStructTypeLiteralStart,
                               CARBON_TOKEN(CloseCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(StructTypeLiteral,
                               StructLiteralOrStructTypeLiteralStart,
                               CARBON_TOKEN(CloseCurlyBrace))

// TODO: Is there a benefit to having different parse node kinds for every
// different modifier token?

// Access modifier keywords `private` or `protected`:
// AccessModifierKeyword
//
// The kind of keyword is determined by looking at the token kind.
// These may be repeated, including possibly zero times.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(AccessModifierKeyword, 0,
                                   CARBON_TOKEN(Private)
                                   CARBON_TOKEN(Protected))

// Declaration modifier keywords such as `abstract` or `virtual`:
// DeclModifierKeyword
//
// The kind of keyword is determined by looking at the token kind.
// These may be repeated, including possibly zero times.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(DeclModifierKeyword, 0,
                                   CARBON_TOKEN(Abstract)
                                   CARBON_TOKEN(Base)
                                   CARBON_TOKEN(Default)
                                   CARBON_TOKEN(Final)
                                   CARBON_TOKEN(Impl)
                                   CARBON_TOKEN(Virtual))

// `class`:
//     ClassIntroducer
//     _repeated_ _external_: AccessModifierKeyword or DeclModifierKeyword
//     _external_: Name or QualifiedDecl
//   ClassDefinitionStart
//   _external_: declarations
// ClassDefinition
//
// The above is the structure for a definition; for a declaration,
// ClassDefinitionStart and later nodes are removed and replaced by
// ClassDecl.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ClassIntroducer, 0, CARBON_TOKEN(Class))
CARBON_PARSE_NODE_KIND_BRACKET(ClassDefinitionStart, ClassIntroducer,
                               CARBON_TOKEN(OpenCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(ClassDefinition, ClassDefinitionStart,
                               CARBON_TOKEN(CloseCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(ClassDecl, ClassIntroducer,
                               CARBON_TOKEN(Semi)
                                   CARBON_IF_ERROR(CARBON_TOKEN(Class)))

// `base`:
//   BaseIntroducer
//   _repeated_ _external_: AccessModifierKeyword or DeclModifierKeyword
//   BaseColon
//   _external_: expression
// BaseDecl
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_TOKEN(Base)))

// `interface`:
//     InterfaceIntroducer
//     _repeated_ _external_: AccessModifierKeyword or DeclModifierKeyword
//     _external_: Name or QualifiedDecl
//   InterfaceDefinitionStart
//   _external_: declarations
// InterfaceDefinition
//
// The above is the structure for a definition; for a declaration,
// InterfaceDefinitionStart and later nodes are removed and replaced by
// InterfaceDecl.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(InterfaceIntroducer, 0,
                                   CARBON_TOKEN(Interface))
CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDefinitionStart, InterfaceIntroducer,
                               CARBON_TOKEN(OpenCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDefinition, InterfaceDefinitionStart,
                               CARBON_TOKEN(CloseCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDecl, InterfaceIntroducer,
                               CARBON_TOKEN(Semi)
                                   CARBON_IF_ERROR(CARBON_TOKEN(Interface)))

// `constraint`:
//     NamedConstraintIntroducer
//     _repeated_ _external_: AccessModifierKeyword or DeclModifierKeyword
//     _external_: Name or QualifiedDecl
//   NamedConstraintDefinitionStart
//   _external_: declarations
// NamedConstraintDefinition
//
// The above is the structure for a definition; for a declaration,
// NamedConstraintDefinitionStart and later nodes are removed and replaced by
// NamedConstraintDecl.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(NamedConstraintIntroducer, 0,
                                   CARBON_TOKEN(Constraint))
CARBON_PARSE_NODE_KIND_BRACKET(NamedConstraintDefinitionStart,
                               NamedConstraintIntroducer,
                               CARBON_TOKEN(OpenCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(NamedConstraintDefinition,
                               NamedConstraintDefinitionStart,
                               CARBON_TOKEN(CloseCurlyBrace))
CARBON_PARSE_NODE_KIND_BRACKET(NamedConstraintDecl, NamedConstraintIntroducer,
                               CARBON_TOKEN(Semi))

// The `self` value and `Self` type identifier keywords. Typically of the form
// `self: Self`:
//   SelfValueName
//   SelfValueNameExpr
//   SelfTypeNameExpr
// BindingPattern
CARBON_PARSE_NODE_KIND_CHILD_COUNT(SelfValueName, 0,
                                   CARBON_TOKEN(SelfValueIdentifier))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(SelfValueNameExpr, 0,
                                   CARBON_TOKEN(SelfValueIdentifier))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(SelfTypeNameExpr, 0,
                                   CARBON_TOKEN(SelfTypeIdentifier))

// The `base` value keyword, introduced by `base: B`. Typically referenced in
// an expression, as in `x.base` or `{.base = ...}`, but can also be used as a
// declared name, as in `{.base: partial B}`.
//
// BaseName
CARBON_PARSE_NODE_KIND_CHILD_COUNT(BaseName, 0, CARBON_TOKEN(Base))

// The `package` keyword in an expression.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PackageExpr, 0, CARBON_TOKEN(Package))

#undef CARBON_PARSE_NODE_KIND
#undef CARBON_PARSE_NODE_KIND_BRACKET
#undef CARBON_PARSE_NODE_KIND_CHILD_COUNT
#undef CARBON_PARSE_NODE_KIND_TOKEN_LITERAL
#undef CARBON_TOKEN
#undef CARBON_ANY_TOKEN
#undef CARBON_IF_ERROR