`PatField` and `ExprField` produce no warning for `#[doc(...)]` attribute

[gurry]

Code

struct X {
    foo: i32,
}

#[allow(unused_variables)] // Not necessary for reproducing. Just to suppress an unrelated warning
fn main() {
    let X {
        #[doc(alias = "PatFieldAlias")]
        foo
    } = X {
        foo: 123
    };

    let _ = X {
        #[doc(alias = "ExprFieldAlias")]
        foo: 123,
    };
}

Current output

No output (compilation succeeds without warning)

Desired output

warning: unused doc comment
   |
14 |       let X {
15 |           #[doc(alias = "PatFieldAlias")]
   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
16 | /         foo
17 | |     } = X {
18 | |         foo: 123
19 | |     };
   | |______- rustdoc does not generate documentation for pattern fields
   |
   = help: use `//` for a plain comment
   = note: `#[warn(unused_doc_comments)]` on by default

warning: unused doc comment
   |
22 |       let _ = X {
23 |           #[doc(alias = "ExprFieldAlias")]
   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
24 | /         foo: 123,
25 | |     };
   | |______- rustdoc does not generate documentation for expression fields
   |
   = help: use `//` for a plain comment
   = note: `#[warn(unused_doc_comments)]` on by default

Rationale and extra context

The same warning is produced at other places like statements, expressions, functions etc. For completeness and consistency it should be produced for pattern and expression fields too.

Other cases

No response

Anything else?

rustc 1.74.0-nightly (35e4163 2023-09-01)
binary: rustc
commit-hash: 35e4163
commit-date: 2023-09-01
host: x86_64-pc-windows-msvc
release: 1.74.0-nightly
LLVM version: 17.0.0

rustc version older than 1.74.0 may ICE on this code. The ICE was fixed in 1.74.0

[gurry]

The reason these warnings are not produced is because the lint infrastructure currently exposes no hooks for PatField and ExprField, i.e. there are no check_pat_field and check_expr_field methods on EarlyLintPass (or LateLintPass for that matter).

To fix the issue, these methods may have to be added here:

rust/compiler/rustc_lint/src/passes.rs

Line 140 in f9ba43c

macro_rules! early_lint_methods {

and then invoked from here:

rust/compiler/rustc_lint/src/early.rs

Lines 113 to 117 in f9ba43c

	fn visit_pat_field(&mut self, field: &'a ast::PatField) {
	self.with_lint_attrs(field.id, &field.attrs, |cx| {
	ast_visit::walk_pat_field(cx, field);
	});
	}

and here:

rust/compiler/rustc_lint/src/early.rs

Lines 131 to 135 in f9ba43c

	fn visit_expr_field(&mut self, f: &'a ast::ExprField) {
	self.with_lint_attrs(f.id, &f.attrs, |cx| {
	ast_visit::walk_expr_field(cx, f);
	})
	}

Alternatively, we can emit the warning from the already existing check_pat and check_expr methods of EarlyLintPass and not bother with the above changes at all.

[compiler-errors]

Alternatively, we can emit the warning from the already existing check_pat and check_expr methods of EarlyLintPass and not bother with the above changes at all.

Yeah, I would expect this is the best way of doing it.

[gurry]

@rustbot claim

[gurry]

@rustbot label -needs-triage