Module rustc_ast::ast

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The Rust abstract syntax tree module.

This module contains common structures forming the language AST. Two main entities in the module are Item (which represents an AST element with additional metadata), and ItemKind (which represents a concrete type and contains information specific to the type of the item).

Other module items worth mentioning:




  • A path like Foo<'a, T>.
  • A constant (expression) that’s not an item or associated item, but needs its own DefId for type-checking, const-eval, etc. These are usually found nested inside types (e.g., array lengths) or expressions (e.g., repeat counts), and also used to define explicit discriminant values for enum variants.
  • An arm of a ‘match’.
  • A constraint on an associated item.
  • A syntax-level representation of an attribute.
  • The mode of a binding (mut, ref mut, etc). Used for both the explicit binding annotations given in the HIR for a binding and the final binding mode that we infer after type inference/match ergonomics. .0 is the by-reference mode (ref, ref mut, or by value), .1 is the mutability of the binding.
  • A block ({ .. }).
  • Delimited arguments, as used in #[attr()/[]/{}] or mac!()/[]/{}.
  • An expression.
  • A single field in a struct expression, e.g. x: value and y in Foo { x: value, y }.
  • Field definition in a struct, variant or union.
  • A signature (not the body) of a function declaration.
  • A function header.
  • Represents a function’s signature in a trait declaration, trait implementation, or free function.
  • Foreign module declaration.
  • Represents lifetime, type and const parameters attached to a declaration of a function, enum, trait, etc.
  • Inline assembly.
  • Inline assembly symbol operands get their own AST node that is somewhat similar to AnonConst.
  • An item definition.
  • A “Label” is an identifier of some point in sources, e.g. in the following code:
  • A “Lifetime” is an annotation of the scope in which variable can be used, e.g. 'a in &'a i32.
  • Local represents a let statement, e.g., let <pat>:<ty> = <expr>;.
  • Represents a macro invocation. The path indicates which macro is being invoked, and the args are arguments passed to it.
  • Represents a macro definition.
  • A semantic representation of a meta item. A meta item is a slightly restricted form of an attribute – it can only contain expressions in certain leaf positions, rather than arbitrary token streams – that is used for most built-in attributes.
  • A literal in a meta item.
  • A method call (e.g.<Bar, Baz>(a, b, c)).
  • A parameter in a function header.
  • A path like Foo(A, B) -> C.
  • A match pattern.
  • A single field in a struct pattern.
  • A “Path” is essentially Rust’s notion of a name.
  • A segment of a path: an identifier, an optional lifetime, and a set of types.
  • The explicit Self type in a “qualified path”. The actual path, including the trait and the associated item, is stored separately. position represents the index of the associated item qualified with this Self type.
  • A static item in extern block.
  • A statement. No attrs or tokens fields because each StmtKind variant contains an AST node with those fields. (Except for StmtKind::Empty, which never has attrs or tokens)
  • Similar to MetaItemLit, but restricted to string literals.
  • Modifiers on a trait bound like ~const, ? and !.
  • TraitRefs appear in impls.
  • The location of a where clause on a TyAlias (Span) and whether there was a where keyword (bool). This is split out from WhereClause, since there are two locations for where clause on type aliases, but their predicates are concatenated together.
  • The span information for the two where clauses on a TyAlias.
  • A tree of paths sharing common prefixes. Used in use items both at top-level and inside of braces in import groups.
  • Enum variant.
  • A type bound.
  • A where-clause in a definition.
  • An equality predicate (unsupported).
  • A lifetime predicate.


Type Aliases§