tabs_in_doc_comments: Clippy flags tab-indented code in doc tests

Summary

The tabs_in_doc_comments complains about tab-indented doctests.

Running cargo doc generates nice-looking and correctly-indented documentation when using tabs in this way, so I see no reason for Clippy to emit a lint.

Note that rustfmt doesn't change the formatting/indentation of doctests like this regardless of whether hard_tabs = true is set in .rustfmt.toml.

Lint Name

tabs_in_doc_comments

Reproducer

I tried this code:

/// ```
/// fn testing() {
/// 	println!("this line is tab-indented")
/// }
/// ```
pub fn foo() {
    println!("Hello, world")
}

I saw this happen:

    Checking clippy-repro v1.4.4 (/home/user/fend/clippy-repro)
warning: using tabs in doc comments is not recommended
 --> clippy-repro/src/lib.rs:3:5
  |
3 | ///     println!("this line is tab-indented")
  |     ^^^^ help: consider using four spaces per tab
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#tabs_in_doc_comments
  = note: `#[warn(clippy::tabs_in_doc_comments)]` on by default

warning: `clippy-repro` (lib) generated 1 warning
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s

I expected to see this happen:
Clippy should not have linted that line.

Version

rustc 1.75.0 (82e1608df 2023-12-21)
binary: rustc
commit-hash: 82e1608dfa6e0b5569232559e3d385fea5a93112
commit-date: 2023-12-21
host: x86_64-unknown-linux-gnu
release: 1.75.0
LLVM version: 17.0.6

Additional Labels

No response

Start with the tabs_in_doc_comments lint and the provided doctest reproducer, then compare its behavior with cargo doc and rustfmt's handling of doctest indentation. Done means tab-indented code inside the documented doctest no longer triggers this lint, while the reported reproduction can still be checked.