AST validation is a separate AST pass that visits each item in the tree and performs simple checks. This pass doesn't perform any complex analysis, type checking or name resolution.
Before performing any validation, the compiler first expands the macros. Then this pass performs validations to check that each AST item is in the correct state. And when this pass is done, the compiler runs the crate resolution pass.
Validations are defined in
AstValidator type, which
itself is located in
rustc_ast_passes crate. This
type implements various simple checks which emit errors
when certain language rules are broken.
that defines how to visit AST items (which can be functions,
traits, enums, etc).
For each item, visitor performs specific checks. For
example, when visiting a function declaration,
AstValidator checks that the function has:
- no more than
- c-variadic functions are declared with at least one named argument;
- c-variadic argument goes the last in the declaration;
- documentation comments aren't applied to function parameters;
- and other validations.