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#[macro_use] does not work on macro-expanded extern crates #33936

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jseyfried opened this issue May 29, 2016 · 2 comments · Fixed by #34032
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#[macro_use] does not work on macro-expanded extern crates #33936

jseyfried opened this issue May 29, 2016 · 2 comments · Fixed by #34032
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A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)

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@jseyfried
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For example, this compiles:

#![feature(rustc_private)]

#[macro_use]
extern crate syntax;

fn main() {
    help!(S, "");

    struct S;
    impl S { fn help(&self, _: &str) {} }
}

but this doesn't:

#![feature(rustc_private)]

macro_rules! my_extern_crate {
    ($i:ident) => { #[macro_use] extern crate $i; }
}
my_extern_crate!(syntax);

fn main() { ... }
@TimNN
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TimNN commented May 29, 2016

Probably the same issue as #28071.

@jseyfried
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@TimNN I believe #28071 is a special case of this issue -- thanks for linking it!

@jseyfried jseyfried mentioned this issue Jun 2, 2016
Merged
@steveklabnik steveklabnik added the A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) label Jun 6, 2016
bors added a commit that referenced this issue Jun 9, 2016
@bors
Auto merge of #34032 - jseyfried:load_macros_in_expansion, r=nrc
dc77c5e 
Support `#[macro_use]` on macro-expanded crates

This PR loads macros from `#[macro_use]` crates during expansion so that
 - macro-expanded `#[macro_use]` crates work (fixes #33936, fixes #28071), and
 - macros imported from crates have the same scope as macros imported from modules.

This is a [breaking-change]. For example, this will break:
```rust
macro_rules! m {
    () => { #[macro_use(foo)] extern crate core; } //~ ERROR imported macro not found
}
m!();
```
Also, this will break:
```rust
macro_rules! try { () => {} }
// #[macro_use] mod bar { macro_rules! try { ... } } //< ... just like this would ...
fn main() { try!(); } //< ... making this an error
```

r? @nrc
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Support #[macro_use] on macro-expanded crates jseyfried/rust
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@steveklabnik @TimNN @jseyfried