[flake8-implicit-str-concat] Mark fix unsafe when it creates a docstring (ISC003)

[mdiniz97]

Fixes #27979

Removing the + from the first statement of a module, function, or class body turns the concatenation into a docstring, changing __doc__ and program behavior. Detect docstring positions and emit the fix with unsafe safety level instead.

• Concats of plain string literals only (f-strings, bytes, t-strings can never be docstrings)
• Covers module, function, class, and method bodies
• Safe fix behavior unchanged for non-docstring positions

Test Plan

cargo test -p ruff_linter --lib (2813 pass), clippy + fmt clean

[ntBre]

Thanks, this looks reasonable overall. I just had a few comments on the tests and a couple of suggestions on simplifying the implementation.

[mdiniz97]

Thanks for the review, @ntBre! All suggestions addressed:

• explicit.rs: use current_statement() / current_statement_parent() directly instead of retrieving ids
• explicit.rs: use Applicability + Fix::applicable_edit instead of if/else on safe/unsafe edit constructors
• Tests: moved all fix-safety cases to a dedicated ISC003_docstring.py fixture so the module case is genuinely in a docstring position (first statement of the module body), and moved the f-string / bytes / nested-expression negatives into docstring positions so they exercise the "right position, wrong type" path

Verified locally: cargo test -p ruff_linter --lib (2814 pass), clippy and fmt clean, and the binary keeps the fix hidden under --fix for module/function/class/method docstring positions while applying it for the negative cases.

[ntBre]

Thanks!

I pushed a small commit trimming down some comments, removing an extra newline, and adding fix safety docs, but this looked good to me.

[astral-sh-bot]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.