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Rollup merge of #82682 - petrochenkov:cfgeval, r=Aaron1011

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Implement built-in attribute macro `#[cfg_eval]` + some refactoring

This PR implements a built-in attribute macro `#[cfg_eval]` as it was suggested in https://github.com/rust-lang/rust/pull/79078 to avoid `#[derive()]` without arguments being abused as a way to configure input for other attributes.

The macro is used for eagerly expanding all `#[cfg]` and `#[cfg_attr]` attributes in its input ("fully configuring" the input).
The effect is identical to effect of `#[derive(Foo, Bar)]` which also fully configures its input before passing it to macros `Foo` and `Bar`, but unlike `#[derive]` `#[cfg_eval]` can be applied to any syntax nodes supporting macro attributes, not only certain items.

`cfg_eval` was the first name suggested in https://github.com/rust-lang/rust/pull/79078, but other alternatives are also possible, e.g. `cfg_expand`.

```rust
#[cfg_eval]
#[my_attr] // Receives `struct S {}` as input, the field is configured away by `#[cfg_eval]`
struct S {
    #[cfg(FALSE)]
    field: u8,
}
```

Tracking issue: https://github.com/rust-lang/rust/issues/82679
This commit is contained in:
Dylan DPC
2021-03-08 13:13:23 +01:00
committed by GitHub
parent 7b78d86d6a 5d27728141
commit 9c310571a8
17 changed files with 453 additions and 259 deletions
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18
compiler/rustc_expand/src/base.rs
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@@ -81,8 +81,22 @@ impl AstLike for Annotatable {
}
}
fn finalize_tokens(&mut self, tokens: LazyTokenStream) {
panic!("Called finalize_tokens on an Annotatable: {:?}", tokens);
fn tokens_mut(&mut self) -> Option<&mut Option<LazyTokenStream>> {
match self {
Annotatable::Item(item) => item.tokens_mut(),
Annotatable::TraitItem(trait_item) => trait_item.tokens_mut(),
Annotatable::ImplItem(impl_item) => impl_item.tokens_mut(),
Annotatable::ForeignItem(foreign_item) => foreign_item.tokens_mut(),
Annotatable::Stmt(stmt) => stmt.tokens_mut(),
Annotatable::Expr(expr) => expr.tokens_mut(),
Annotatable::Arm(arm) => arm.tokens_mut(),
Annotatable::Field(field) => field.tokens_mut(),
Annotatable::FieldPat(fp) => fp.tokens_mut(),
Annotatable::GenericParam(gp) => gp.tokens_mut(),
Annotatable::Param(p) => p.tokens_mut(),
Annotatable::StructField(sf) => sf.tokens_mut(),
Annotatable::Variant(v) => v.tokens_mut(),
}
}
}