Incorrect missing docs lint for proc-macro-lib crates

[mthebridge]

proc-macro-lib crates, when compiled with -W missing-docs, generate invalid warnings about missing documentation.

The following simple crate demonstrates the error.

src/lib.rs:

//! Custom derive module
extern crate proc_macro;

use proc_macro::TokenStream;

/// Derive IntoIterator
#[proc_macro_derive(IntoIterator)]
pub fn into_iterator(_input: TokenStream) -> TokenStream {
    unimplemented!()
}

Cargo.toml:

[package]
name = "tmp"
version = "0.1.0"

[lib]
proc-macro = true

I expect this to compile cleanly since there is a crate-level doc comment and a doc comment for the public function.

Instead, compiling gives:

warning: missing documentation for a module [-W missing-docs]
 --> src/lib.rs:1:1
  |
1 | //! Custom derive module
  | ^

warning: missing documentation for a function [-W missing-docs]
 --> src/lib.rs:1:1
  |
1 | //! Custom derive module
  | ^

which makes no sense since line 1 is a comment.

Compiler version - latest stable, but fails on yesterday's nightly (2017-05-14) too:

rustc --version --verbose:

rustc 1.17.0 (56124baa9 2017-04-24)
binary: rustc
commit-hash: 56124baa9e73f28c0709e59e74783cf234a978cf
commit-date: 2017-04-24
host: x86_64-unknown-linux-gnu
release: 1.17.0
LLVM version: 3.9

[Mark-Simulacrum]

cc #38356 (tracking issue)

[d-e-s-o]

I am hitting the same problem. This issue is preventing #![deny(missing_docs)] for proc-macro crates (I haven't found a work around). That's pretty annoying :-/ Rust 1.24.1.

[H2CO3]

Same here. Is there a fix for this?

[JeanMertz]

Seems to still be happening.

[repnop]

Fails on stable, beta, and nightly still.

[dbeckwith]

On a proc-macro crate in nightly-2019-01-02, I'm getting two warnings: missing documentation for a module and missing documentation for a static with no line numbers.

[iliekturtles]

cargo +nightly expand shows that the compiler is inserting a pub mod with a pub static. I didn't find the code that does the insertion in a very brief search.

//your proc_macro's mod.rs code...

pub mod decls {
    extern crate proc_macro;
    #[rustc_proc_macro_decls]
    pub static _DECLS: &[proc_macro::bridge::client::ProcMacro] =
        &[proc_macro::bridge::client::ProcMacro::bang(
            "your_proc_macro",
            crate::your_proc_macro,
        )];
}

[remexre]

So I guess the low-effort fix here is slapping #[doc(hidden)] on that mod?

EDIT: Looks like the code that generates that is

rust/src/libsyntax_ext/proc_macro_decls.rs

Lines 339 to 344 in fcf850f

	fn mk_decls(
	cx: &mut ExtCtxt<'_>,
	custom_derives: &[ProcMacroDerive],
	custom_attrs: &[ProcMacroDef],
	custom_macros: &[ProcMacroDef],
	) -> P<ast::Item> {

?

[iliekturtles]

Thanks @remexre! Turns out my working copy wasn't updated like I thought so searching through it didn't work. PR #60562 just submitted.