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Proc macro gives bad error about custom derives if regular macro with the same name is imported first #39326

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Arnavion opened this issue Jan 26, 2017 · 3 comments

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@Arnavion
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Arnavion commented Jan 26, 2017

rustc 1.16.0-nightly (7821a9b 2017-01-23)

main.rs

#[macro_use] extern crate derive_error_chain;
#[macro_use] extern crate error_chain;

#[derive(Debug, error_chain)]
pub enum ErrorKind {
    Msg(String),
}

fn main() {
}

Cargo.toml

[package]
name = "rust-test"
version = "0.1.0"
authors = ["Arnavion <arnavion@gmail.com>"]

[dependencies]
derive-error-chain = "=0.8.0"
error-chain = "=0.8.1"

cargo build gives:

error: `#[derive]` for custom traits is not stable enough for use. It is deprecated and will be removed in v1.15 (see issue #29644)
 --> src\main.rs:4:17
  |
4 | #[derive(Debug, error_chain)]
  |                 ^^^^^^^^^^^
  |
  = help: add #![feature(custom_derive)] to the crate attributes to enable

error: aborting due to previous error

derive-error-chain exports a proc macro named error_chain. error-chain exports a regular macro named error_chain.

Everything's fine if the order of the extern crate statements is reversed, or error-chain's import does not have #[macro_use].

@keeperofdakeys
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keeperofdakeys commented Jan 30, 2017

Unfortunately macro_rules, proc-macro derives, and future proc-macros share the same namespace. So I don't think there is a way to fix this besides renaming one of the macros.

@nrc ?

@Arnavion
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I'm not asking for a way to make this work. I'm asking for an error message that isn't misleading :)

@keeperofdakeys
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Ah, I'm actually working on a PR right now which should fix this, I'll be sure to keep it in mind #39391.

frewsxcv added a commit to frewsxcv/rust that referenced this issue Feb 5, 2017
…eyfried

Expand derive macros in the MacroExpander

This removes the expand_derives function, and sprinkles the functionality throughout the Invocation Collector, Expander and Resolver.

Fixes rust-lang#39326

r? @jseyfried
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