Doc comments on modules are included twice in AST

[zslayton]

Following up on an issue first discovered in #12386. ///-style Doc comments placed on pub mod lines appear twice in the AST.

In this minimal example, there are two files: mod.rs and test.rs.

mod.rs contains:

/// The 'test' module is elegant in its minimalism. 
pub mod test;

test.rs contains:

/*! This summary statement describes the 'test' module */
pub fn print_test_message() {
   println!("I am a test message.");
}

Compiling with rustc -Z ast-json mod.rs produces the following AST fragment:

    "items": [
      {
        "ident": "test",
        "attrs": [
          {
            "node": {
              "style": "AttrOuter",
              "value": {
                "node": [
                  "MetaNameValue",
                  "doc",
                  {
                    "node": [
                      "LitStr",
                      "/// The 'test' module is elegant in its minimalism. ",
                      "CookedStr"
                    ],
                    "span": null
                  }
                ],
                "span": null
              },
              "is_sugared_doc": true
            },
            "span": null
          },
          {
            "node": {
              "style": "AttrOuter",
              "value": {
                "node": [
                  "MetaNameValue",
                  "doc",
                  {
                    "node": [
                      "LitStr",
                      "/// The 'test' module is elegant in its minimalism. ",
                      "CookedStr"
                    ],
                    "span": null
                  }
                ],
                "span": null
              },
              "is_sugared_doc": true
            },
            "span": null
          }
// .... remainder of AST follows

The complete AST can be found here.

[huonw]

A minimal test seems to be:

/// The 'test' module is elegant in its minimalism.
mod test;

with an empty test.rs, and it doesn't trigger with an inline mod test {}, i.e. it's caused by having multiple files.

[zslayton]

I retried the minimal test cases described here and the problem appears to have been resolved at some point. Shall I close the ticket or is there some additional procedure to consider?

[steveklabnik]

Nope, that's it.