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Macro invocations allow type parameters in the path #28558

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Manishearth opened this issue Sep 21, 2015 · 6 comments · Fixed by #34495
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Macro invocations allow type parameters in the path #28558

Manishearth opened this issue Sep 21, 2015 · 6 comments · Fixed by #34495
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A-grammar Area: The grammar of Rust A-parser Area: The parsing of Rust source code to an AST. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@Manishearth
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vec::<T,U,V,W::X::Y<Z>>![1,2,3,4]; is valid syntax and compiles to a regular vector.

This is because macros use Paths, not Idents as their names. Multi-segment paths are disallowed, but the path can have type parameters.

We can move macros to Idents, however this would not be backwards compatible since anyone using vec::<T>![1,2] would get a syntax error (even though the original syntax is meaningless). It's still a bug, so perhaps we can get away with this breaking change.

Thoughts?

cc @eddyb @alexcrichton
@Manishearth Manishearth added I-wrong A-grammar Area: The grammar of Rust A-parser Area: The parsing of Rust source code to an AST. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 21, 2015
@eddyb
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eddyb commented Sep 21, 2015

I'd say fix it and do a crater run.

@alexcrichton
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Sounds like a plan to me

@DemiMarie
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Ping?

@eddyb
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eddyb commented Jun 27, 2016

@drbo I don't think anyone worked on it.
In case someone wants to work on it, the two relevant points are type macros and expressions macros.
It should be possible to error if the path is absolute, has more than one component, or any lifetime/type parameters. We can then do a crater run to see if these are used in the wild for some reason.

@eddyb
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eddyb commented Jun 27, 2016

cc @jseyfried @petrochenkov @nrc

@jseyfried jseyfried mentioned this issue Jun 27, 2016
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@jseyfried
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I fixed this in #34495.

Manishearth added a commit to Manishearth/rust that referenced this issue Jun 29, 2016
@Manishearth
Rollup merge of rust-lang#34495 - jseyfried:only_ident_macro_invocati…
8886818 
…ons, r=eddyb

Forbid type parameters and global paths in macro invocations

Fixes rust-lang#28558.
This is a [breaking-change]. For example, the following would break:
```rust
macro_rules! m { () => { () } }
fn main() {
    m::<T>!(); // Type parameters are no longer allowed in macro invocations
    ::m!(); // Global paths are no longer allowed in macro invocations
}
```
Any breakage can be fixed by removing the type parameters or the leading `::` (respectively).

r? @eddyb
@jethrogb jethrogb mentioned this issue Dec 2, 2016
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A-grammar Area: The grammar of Rust A-parser Area: The parsing of Rust source code to an AST. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Forbid type parameters and global paths in macro invocations jseyfried/rust
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@alexcrichton @eddyb @Manishearth @DemiMarie @jseyfried