Add a lint to warn on T: Drop bounds
#3776
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Idk how hard it is to create a structured suggestion for this lint, but I'd be delighted if you tried to create one. Maybe modify a copy of the AST in place and pretty print that? |
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I don't think suggestions would help very much. While "just remove the bound" would "fix" the code in the sense that it would stop the lint from firing and it wouldn't break anything that worked, the proper way to fix it is to switch to |
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I also just realized that I hadn't actually tested this with |
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**What it does:** Checks for generics with `std::ops::Drop` as bounds.
**Why is this bad?** `Drop` bounds do not really accomplish anything.
A type may have compiler-generated drop glue without implementing the
`Drop` trait itself. The `Drop` trait also only has one method,
`Drop::drop`, and that function is by fiat not callable in user code.
So there is really no use case for using `Drop` in trait bounds.
**Known problems:** None.
**Example:**
```rust
fn foo<T: Drop>() {}
```
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r=me with docs nit and travis passing |
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Okay, @oli-obk. Fixed the formatting that Travis complained about and added the second paragraph to why-it's-bad. |
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@bors r+ superb, thanks! |
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📌 Commit bc4c3b6 has been approved by |
Add a lint to warn on `T: Drop` bounds
**What it does:** Checks for generics with `std::ops::Drop` as bounds.
**Why is this bad?** `Drop` bounds do not really accomplish anything.
A type may have compiler-generated drop glue without implementing the
`Drop` trait itself. The `Drop` trait also only has one method,
`Drop::drop`, and that function is by fiat not callable in user code.
So there is really no use case for using `Drop` in trait bounds.
**Known problems:** None.
**Example:**
```rust
fn foo<T: Drop>() {}
```
Fixes #3773
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☀️ Test successful - checks-travis, status-appveyor |
What it does: Checks for generics with
std::ops::Dropas bounds.Why is this bad?
Dropbounds do not really accomplish anything.A type may have compiler-generated drop glue without implementing the
Droptrait itself. TheDroptrait also only has one method,Drop::drop, and that function is by fiat not callable in user code.So there is really no use case for using
Dropin trait bounds.Known problems: None.
Example:
Fixes #3773