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Mazdak Farrokhzad
16939a50ea
Ensure that drop order of `async fn` matches `fn` and that users cannot refer to generated arguments. Fixes #60236 and fixes #60438. This PR modifies the lowering of `async fn` arguments so that the drop order matches the equivalent `fn`. Previously, async function arguments were lowered as shown below: async fn foo(<pattern>: <ty>) { async move { } } // <-- dropped as you "exit" the fn // ...becomes... fn foo(__arg0: <ty>) { async move { let <pattern> = __arg0; } // <-- dropped as you "exit" the async block } After this PR, async function arguments will be lowered as: async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) { async move { } } // <-- dropped as you "exit" the fn // ...becomes... fn foo(__arg0: <ty>, __arg1: <ty>, __arg2: <ty>) { async move { let __arg2 = __arg2; let <pattern> = __arg2; let __arg1 = __arg1; let <pattern> = __arg1; let __arg0 = __arg0; let <pattern> = __arg0; } // <-- dropped as you "exit" the async block } If `<pattern>` is a simple ident, then it is lowered to a single `let <pattern> = <pattern>;` statement as an optimization. This PR also stops users from referring to the generated `__argN` identifiers. r? @nikomatsakis
The syntax crate contains those things concerned purely with syntax
– that is, the AST ("abstract syntax tree"), parser, pretty-printer,
lexer, macro expander, and utilities for traversing ASTs.
For more information about how these things work in rustc, see the rustc guide: