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pickx opened this issue Apr 22, 2023 · 1 comment · Fixed by #14816
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assist: replace generic with impl trait #14626

pickx opened this issue Apr 22, 2023 · 1 comment · Fixed by #14816
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@justahero
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A-assists C-feature Category: feature request

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pickx commented Apr 22, 2023 •
edited by rustbot
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fn new<P: AsRef<Path>>(location: P) -> Self { }

Placing the cursor on P: AsRef<Path> or on the P of location: P should trigger an assist to change this to

fn new(location: impl AsRef<Path>) -> Self { }

We already have an assist replace impl trait with generic that does the opposite.
@pickx pickx added the C-feature Category: feature request label Apr 22, 2023
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@justahero justahero mentioned this issue May 16, 2023
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@bors bors closed this as completed in e963846 May 26, 2023
@justahero justahero mentioned this issue Jun 2, 2023
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bors added a commit that referenced this issue Jun 2, 2023
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Auto merge of #14945 - justahero:gh-14626, r=Veykril
7738ff4 
Fix Assist "replace named generic type with impl trait"

This is a follow-up PR to fix the assist "replace named generic type with impl trait" described in #14626 to filter invalid param types. It integrates the feedback given in PR #14816 .

The change updates the logic to determine when a function parameter is safe to replace a type param with its trait implementation. Some parameter definitions are invalid & should not be replaced by their traits, therefore skipping the assist completely.

First, all usages of the generic type under the cursor are determined. These usage references are checked to see if they occur outside the function parameter list. If an outside reference is found, e.g. in body, return type or where clause, the assist is skipped. All remaining usages need to appear only in the function param list. For each usage the param type is further inspected to see if it's valid. The logic to determine if a function parameter is valid, follows a heuristic and may not cover all possible parameter definitions.

With this change the following param types (as given in [this comment](#14816 (comment))) are not replaced & therefore skip the assist.

```rust
fn foo<P: Trait>(
    _: <P as Trait>::Assoc,          // within path type qualifier
    _: <() as OtherTrait<P>>::Assoc, // same as above
    _: P::Assoc,                     // associated type shorthand
    _: impl OtherTrait<P>            // generic arg in impl trait (note that associated type bindings are fine)
    _: &dyn Fn(P)                    // param type and/or return type for Fn* traits
) {}
```
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feat: Assist to replace generic with impl trait
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@justahero @Veykril @pickx