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.
//   - CARBON_PARSE_NODE_KIND_BRACKET(Name, BracketName, LexTokenKind)
//     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, LexTokenKind)
//     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_PREFIX_OPERATOR(Name)
//       Defines a parse node for a prefix operator, with the Name as token.
//     - CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Name)
//       Defines a parse node for an infix operator, with the Name as token.
//     - CARBON_PARSE_NODE_KIND_POSTFIX_OPERATOR(Name)
//       Defines a parse node for a postfix operator, with the Name as token.
//     - CARBON_PARSE_NODE_KIND_TOKEN_LITERAL(Name, LexTokenKind)
//       Defines a parse node that corresponds to a token that is a single-token
//       literal. The token is wrapped for LexTokenKinds.
//     - CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Name)
//       A token-based modifier. The Name is the TokenKind, and will be appended
//       with "Modifier" for the parse kind.
//
// LexTokenKind indicates the token kind required on a valid node.
// It will be either `kind_name` to indicate it's required even if the node is
// an error, or `CARBON_IF_VALID(kind_name)` to indicate that the kind is
// not enforced on error. A token kind of `Error` may be used if the kind should
// never be enforced; this should only be used when the node is either not in
// trees (`Placeholder`) or is always invalid (such as `InvalidParse`).
//
// 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 modifier cases.
//   #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) \
  CARBON_PARSE_NODE_KIND_CHILD_COUNT(PrefixOperator##Name, 1, Name)
#endif

// This is expected to be used with something like:
//
//   // Use x-macros to handle modifier cases.
//   #define CARBON_PARSE_NODE_KIND(...)
//   #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, Name)
#endif

// This is expected to be used with something like:
//
//   // Use x-macros to handle modifier cases.
//   #define CARBON_PARSE_NODE_KIND(...)
//   #define CARBON_PARSE_NODE_KIND_POSTFIX_OPERATOR(Name, ...) <code>
#ifndef CARBON_PARSE_NODE_KIND_POSTFIX_OPERATOR
#define CARBON_PARSE_NODE_KIND_POSTFIX_OPERATOR(Name) \
  CARBON_PARSE_NODE_KIND_CHILD_COUNT(PostfixOperator##Name, 1, 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

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

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

// The end of the file.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(FileEnd, 0, FileEnd)

// An invalid parse. Used to balance the parse tree. Always has an error.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(InvalidParse, 0, Error)

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

// A placeholder node to be replaced; it will never exist in a valid parse tree.
// Its token kind is not enforced even when valid.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(Placeholder, 0, Error)

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

// An identifier name in a non-expression context, such as a declaration.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(IdentifierName, 0,
                                   CARBON_IF_VALID(Identifier))

// An identifier name in an expression context.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(IdentifierNameExpr, 0, Identifier)

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

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

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

// 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, Identifier)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(LibraryName, 0, StringLiteral)

// `package`:
//   PackageIntroducer
//   _optional_ _external_: PackageName
//   _optional_ _external_: LibrarySpecifier
//   PackageApi or PackageImpl
// PackageDirective
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PackageIntroducer, 0, Package)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PackageApi, 0, Api)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PackageImpl, 0, Impl)
CARBON_PARSE_NODE_KIND_BRACKET(PackageDirective, PackageIntroducer,
                               CARBON_IF_VALID(Semi))

// `import`:
//   ImportIntroducer
//   _optional_ _external_: PackageName
//   _optional_ _external_: LibrarySpecifier
// ImportDirective
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ImportIntroducer, 0, Import)
CARBON_PARSE_NODE_KIND_BRACKET(ImportDirective, ImportIntroducer,
                               CARBON_IF_VALID(Semi))
// `library` as directive:
//   LibraryIntroducer
//   DefaultLibrary or _external_: LibraryName
//   PackageApi or PackageImpl
// LibraryDirective
CARBON_PARSE_NODE_KIND_CHILD_COUNT(DefaultLibrary, 0, Default)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(LibraryIntroducer, 0, Library)
CARBON_PARSE_NODE_KIND_BRACKET(LibraryDirective, LibraryIntroducer,
                               CARBON_IF_VALID(Semi))

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

// `namespace`:
//   NamespaceStart
//   _repeated_ _external_: modifier
//   _external_: IdentifierName or QualifiedName
// Namespace
CARBON_PARSE_NODE_KIND_CHILD_COUNT(NamespaceStart, 0, Namespace)
CARBON_PARSE_NODE_KIND_BRACKET(Namespace, NamespaceStart, CARBON_IF_VALID(Semi))

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

// `fn`:
//     FunctionIntroducer
//     _repeated_ _external_: modifier
//     _external_: IdentifierName or QualifiedName
//     _optional_ _external_: ImplicitParamList
//     _external_: TuplePattern
//       _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, Fn)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ReturnType, 1, MinusGreater)
CARBON_PARSE_NODE_KIND_BRACKET(FunctionDefinitionStart, FunctionIntroducer,
                               OpenCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(FunctionDefinition, FunctionDefinitionStart,
                               CloseCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(FunctionDecl, FunctionIntroducer,
                               CARBON_IF_VALID(Semi))

// A tuple pattern:
//   TuplePatternStart
//     _external_: [Generic]BindingPattern
//     PatternListComma
//   _repeated_
// TuplePattern
//
// Patterns and PatternListComma may repeat with PatternListComma as a
// separator.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(TuplePatternStart, 0, OpenParen)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(PatternListComma, 0, Comma)
CARBON_PARSE_NODE_KIND_BRACKET(TuplePattern, TuplePatternStart, CloseParen)

// An implicit parameter list:
//   ImplicitParamListStart
//     _external_: [Generic]BindingPattern
//     PatternListComma
//   _repeated_
// ImplicitParamList
//
// Patterns and PatternListComma may repeat with PatternListComma as a
// separator.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ImplicitParamListStart, 0, OpenSquareBracket)
CARBON_PARSE_NODE_KIND_BRACKET(ImplicitParamList, ImplicitParamListStart,
                               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, OpenSquareBracket)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ArrayExprSemi, 2, CARBON_IF_VALID(Semi))
CARBON_PARSE_NODE_KIND_BRACKET(ArrayExpr, ArrayExprSemi, CloseSquareBracket)

// A binding pattern, such as `name: Type`:
//       IdentifierName or SelfValueName
//       _external_: type expression
//     [Generic]BindingPattern
//   _optional_ Address
// _optional_ Template
//
// TODO: Rename GenericBindingPattern to CompileTimeBindingPattern.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(BindingPattern, 2, CARBON_IF_VALID(Colon))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(GenericBindingPattern, 2, ColonExclaim)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(Address, 1, Addr)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(Template, 1, Template)

// `let`:
//   LetIntroducer
//   _repeated_ _external_: modifier
//   _external_: BindingPattern or TuplePattern
//   LetInitializer
//   _external_: expression
// LetDecl
//
// Modifier keywords only appear for `let` declarations, not `let` statements.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(LetIntroducer, 0, Let)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(LetInitializer, 0, Equal)
CARBON_PARSE_NODE_KIND_BRACKET(LetDecl, LetIntroducer, CARBON_IF_VALID(Semi))

// `var` and `returned var`:
//   VariableIntroducer
//   _repeated_ _external_: modifier
//   _optional_ ReturnedModifier
//   _external_: BindingPattern or TuplePattern
//     _external_: expression
//   _optional_ VariableInitializer
// 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_IF_VALID(Var))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ReturnedModifier, 0, Returned)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(VariableInitializer, 1, Equal)
CARBON_PARSE_NODE_KIND_BRACKET(VariableDecl, VariableIntroducer,
                               CARBON_IF_VALID(Semi))

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

// `break`:
//   BreakStatementStart
// BreakStatement
CARBON_PARSE_NODE_KIND_CHILD_COUNT(BreakStatementStart, 0, Break)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(BreakStatement, 1, CARBON_IF_VALID(Semi))

// `continue`:
//   ContinueStatementStart
// ContinueStatement
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ContinueStatementStart, 0, Continue)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ContinueStatement, 1, CARBON_IF_VALID(Semi))

// `return`:
//   ReturnStatementStart
//   _optional_ ReturnVarModifier or _external_: expression
// ReturnStatement
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ReturnStatementStart, 0, Return)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ReturnVarModifier, 0, Var)
CARBON_PARSE_NODE_KIND_BRACKET(ReturnStatement, ReturnStatementStart,
                               CARBON_IF_VALID(Semi))

// `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_IF_VALID(OpenParen))
CARBON_PARSE_NODE_KIND_BRACKET(ForIn, VariableIntroducer, CARBON_IF_VALID(In))
CARBON_PARSE_NODE_KIND_BRACKET(ForHeader, ForHeaderStart,
                               CARBON_IF_VALID(CloseParen))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ForStatement, 2, 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_IF_VALID(OpenParen))
CARBON_PARSE_NODE_KIND_BRACKET(IfCondition, IfConditionStart,
                               CARBON_IF_VALID(CloseParen))
CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfStatementElse, 0, Else)
CARBON_PARSE_NODE_KIND_BRACKET(IfStatement, IfCondition, If)

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

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

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

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

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

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

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

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

// A prefix operator, such as `not`:
//   _external_: expression
// PrefixOperator<name>
CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Amp)
CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Caret)
CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Const)
CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Not)
CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Minus)
CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(MinusMinus)
CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(PlusPlus)
CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR(Star)

// An infix operator, such as `+`:
//   _external_: lhs expression
//   _external_: rhs expression
// InfixOperator<name>
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Amp)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(AmpEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(As)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Caret)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(CaretEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Equal)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(EqualEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(ExclaimEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Greater)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(GreaterEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(GreaterGreater)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(GreaterGreaterEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Less)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(LessEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(LessEqualGreater)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(LessLess)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(LessLessEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Minus)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(MinusEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Percent)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(PercentEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Pipe)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(PipeEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Plus)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(PlusEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Slash)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(SlashEqual)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(Star)
CARBON_PARSE_NODE_KIND_INFIX_OPERATOR(StarEqual)

// A postfix operator, currently only `*`:
//   _external_: expression
// PostfixOperator<name>
CARBON_PARSE_NODE_KIND_POSTFIX_OPERATOR(Star)

// A short-circuiting infix operator, such as `and`:
//     _external_: expression
//   ShortCircuitOperand(And|Or)
//   _external_: expression
// ShortCircuitOperand(And|Or)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ShortCircuitOperandAnd, 1, And)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ShortCircuitOperandOr, 1, Or)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ShortCircuitOperatorAnd, 2, And)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ShortCircuitOperatorOr, 2, Or)

// `if` expression + `then` + `else`:
//     _external_: expression
//   IfExprIf
//     _external_: expression
//   IfExprThen
//   _external_: expression
// IfExprElse
CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfExprIf, 1, If)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfExprThen, 1, Then)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(IfExprElse, 3, CARBON_IF_VALID(Else))

// Struct literals, such as `{.a = 0}`:
//   StructLiteralOrStructTypeLiteralStart
//         _external_: IdentifierName or BaseName
//       StructFieldDesignator
//       _external_: expression
//     StructFieldValue
//     StructComma
//   _repeated_
// StructLiteral
//
// Struct type literals, such as `{.a: i32}`:
//   StructLiteralOrStructTypeLiteralStart
//         _external_: IdentifierName or BaseName
//       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 InvalidParse, which may have a preceding sibling
// StructFieldDesignator if one was successfully parsed.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructLiteralOrStructTypeLiteralStart, 0,
                                   OpenCurlyBrace)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructFieldDesignator, 1, Period)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructFieldValue, 2, Equal)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructFieldType, 2, Colon)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(StructComma, 0, Comma)
CARBON_PARSE_NODE_KIND_BRACKET(StructLiteral,
                               StructLiteralOrStructTypeLiteralStart,
                               CloseCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(StructTypeLiteral,
                               StructLiteralOrStructTypeLiteralStart,
                               CloseCurlyBrace)

// Various modifiers. These are all a single token.
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Abstract)
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Base)
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Default)
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Extend)
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Final)
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Impl)
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Private)
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Protected)
CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Virtual)

// `class`:
//     ClassIntroducer
//     _repeated_ _external_: modifier
//     _external_: IdentifierName or QualifiedName
//     _optional_ _external_: ImplicitParamList
//     _optional_ _external_: TuplePattern
//   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, Class)
CARBON_PARSE_NODE_KIND_BRACKET(ClassDefinitionStart, ClassIntroducer,
                               OpenCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(ClassDefinition, ClassDefinitionStart,
                               CloseCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(ClassDecl, ClassIntroducer,
                               CARBON_IF_VALID(Semi))

// `base`:
//   BaseIntroducer
//   _repeated_ _external_: modifier
//   BaseColon
//   _external_: expression
// BaseDecl
CARBON_PARSE_NODE_KIND_CHILD_COUNT(BaseIntroducer, 0, Base)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(BaseColon, 0, Colon)
CARBON_PARSE_NODE_KIND_BRACKET(BaseDecl, BaseIntroducer, CARBON_IF_VALID(Semi))

// `interface`:
//     InterfaceIntroducer
//     _repeated_ _external_: modifier
//     _external_: IdentifierName or QualifiedName
//     _optional_ _external_: ImplicitParamList
//     _optional_ _external_: TuplePattern
//   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, Interface)
CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDefinitionStart, InterfaceIntroducer,
                               OpenCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDefinition, InterfaceDefinitionStart,
                               CloseCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(InterfaceDecl, InterfaceIntroducer,
                               CARBON_IF_VALID(Semi))

// `impl ... as`:
//     ImplIntroducer
//     _repeated_ _external_: modifier
//     _optional_ ImplForall (see below)
//     _optional_ _external_: expression
//     ImplAs
//     _external_: expression
//   ImplDefinitionStart
//   _external_: declarations
// ImplDefinition
//
// The above is the structure for a definition; for a declaration,
// ImplDefinitionStart and later nodes are removed and replaced by
// ImplDecl.
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ImplIntroducer, 0, Impl)

// `forall ...`:
//   _external_: ImplicitParamList
// ImplForall
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ImplForall, 1, Forall)
CARBON_PARSE_NODE_KIND_CHILD_COUNT(ImplAs, 0, As)
CARBON_PARSE_NODE_KIND_BRACKET(ImplDefinitionStart, ImplIntroducer,
                               OpenCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(ImplDefinition, ImplDefinitionStart,
                               CloseCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(ImplDecl, ImplIntroducer, CARBON_IF_VALID(Semi))

// `constraint`:
//     NamedConstraintIntroducer
//     _repeated_ _external_: modifier
//     _external_: IdentifierName or QualifiedName
//     _optional_ _external_: ImplicitParamList
//     _optional_ _external_: TuplePattern
//   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, Constraint)
CARBON_PARSE_NODE_KIND_BRACKET(NamedConstraintDefinitionStart,
                               NamedConstraintIntroducer, OpenCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(NamedConstraintDefinition,
                               NamedConstraintDefinitionStart, CloseCurlyBrace)
CARBON_PARSE_NODE_KIND_BRACKET(NamedConstraintDecl, NamedConstraintIntroducer,
                               CARBON_IF_VALID(Semi))

#undef CARBON_PARSE_NODE_KIND
#undef CARBON_PARSE_NODE_KIND_BRACKET
#undef CARBON_PARSE_NODE_KIND_CHILD_COUNT
#undef CARBON_PARSE_NODE_KIND_INFIX_OPERATOR
#undef CARBON_PARSE_NODE_KIND_POSTFIX_OPERATOR
#undef CARBON_PARSE_NODE_KIND_PREFIX_OPERATOR
#undef CARBON_PARSE_NODE_KIND_TOKEN_LITERAL
#undef CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER
#undef CARBON_IF_VALID