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Ensure that drop order of async fn matches fn and that users cannot refer to generated arguments. #60437

Merged
merged 3 commits into from
May 2, 2019
Merged

Ensure that drop order of async fn matches fn and that users cannot refer to generated arguments. #60437

merged 3 commits into from
May 2, 2019

Commits on May 1, 2019

  1. Ensure that drop order of async fn matches fn. 

    This commit 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.
    @davidtwco
    davidtwco committed May 1, 2019
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  2. Ensure that users cannot use generated arguments. 

    This commit gensyms the generated ident for replacement arguments so
that users cannot refer to them. It also ensures that levenshtein
distance suggestions do not suggest gensymed identifiers.
    @davidtwco
    davidtwco committed May 1, 2019
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  3. Unify tests under async-await directory.

    @davidtwco
    davidtwco committed May 1, 2019
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