diff options
| -rw-r--r-- | compiler/rustc_ast_passes/src/ast_validation.rs | 24 |
1 files changed, 17 insertions, 7 deletions
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs index ba4b6130b60..79ee5c0e8e2 100644 --- a/compiler/rustc_ast_passes/src/ast_validation.rs +++ b/compiler/rustc_ast_passes/src/ast_validation.rs @@ -1,10 +1,20 @@ -// Validate AST before lowering it to HIR. -// -// This pass is supposed to catch things that fit into AST data structures, -// but not permitted by the language. It runs after expansion when AST is frozen, -// so it can check for erroneous constructions produced by syntax extensions. -// This pass is supposed to perform only simple checks not requiring name resolution -// or type checking or some other kind of complex analysis. +//! Validate AST before lowering it to HIR. +//! +//! This pass intends to check that the constructed AST is *syntactically valid* to allow the rest +//! of the compiler to assume that the AST is valid. These checks cannot be performed during parsing +//! because attribute macros are allowed to accept certain pieces of invalid syntax such as a +//! function without body outside of a trait definition: +//! +//! ```ignore (illustrative) +//! #[my_attribute] +//! mod foo { +//! fn missing_body(); +//! } +//! ``` +//! +//! These checks are run post-expansion, after AST is frozen, to be able to check for erroneous +//! constructions produced by proc macros. This pass is only intended for simple checks that do not +//! require name resolution or type checking, or other kinds of complex analysis. use itertools::{Either, Itertools}; use rustc_ast::ptr::P; |