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Rollup merge of #62330 - SimonSapin:no-drop-in-union-fields, r=RalfJung

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Change untagged_unions to not allow union fields with drop

This is a rebase of #56440, massaged to solve merge conflicts and make the test suite pass.

Change untagged_unions to not allow union fields with drop

Union fields may now never have a type with attached destructor. This for example allows unions to use arbitrary field types only by wrapping them in `ManuallyDrop` (or similar).

The stable rule remains, that union fields must be `Copy`. We use the new rule for the `untagged_union` feature.

Tracking issue: https://github.com/rust-lang/rust/issues/55149
This commit is contained in:
Mazdak Farrokhzad 2019-10-21 22:00:45 +02:00 • committed by GitHub
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24
src/doc/rustc/src/lints/listing/warn-by-default.md
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@ -596,30 +596,6 @@ warning: function cannot return without recursing
|
```
## unions-with-drop-fields
This lint detects use of unions that contain fields with possibly non-trivial drop code. Some
example code that triggers this lint:
```rust
#![feature(untagged_unions)]
union U {
s: String,
}
```
This will produce:
```text
warning: union contains a field with possibly non-trivial drop code, drop code of union fields is ignored when dropping the union
--> src/main.rs:4:5
|
4 | s: String,
| ^^^^^^^^^
|
```
## unknown-lints
This lint detects unrecognized lint attribute. Some