| # AST validation |
| |
| _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 |
| |
| 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. |
| |
| In addition, `AstValidator` implements `Visitor` trait |
| 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 `u16::MAX` parameters; |
| * c-variadic argument goes the last in the declaration; |
| * documentation comments aren't applied to function parameters; |
| * and other validations. |
