1.16 regression: --warn-unused-ignore now complains in ignored-but-correct places #19237

this appears to have changed behaviour in mypy 1.15 -- I personally prefer the behaviour in 1.15 but would understand if it needed to change. I don't see it mentioned in the changelog however

Bug Report

we're working on incrementally typing a large codebase -- often this means fixing a particular callsite or file at a time (sometimes by intentionally ignoring errors unfortunately)

it seems that in a module with a particular error code (temporarily) disabled, --warn-unused-ignores will complain about a "correct" type ignore (I say "correct" here as it will complain when the file is no longer blocklisted) -- will provide a small example below

To Reproduce

# t.py
def f() -> None:
    x: int = 'hi'  # type: ignore[assignment]

[mypy]
warn_unused_ignores = true
[mypy-t]
disable_error_code = assignment

Expected Behavior

$ mypy --version
mypy 1.15.0 (compiled: yes)
$ mypy t.py
Success: no issues found in 1 source file

Actual Behavior

$ mypy --version
mypy 1.16.0 (compiled: yes)
$ mypy t.py
t.py:2: error: Unused "type: ignore" comment  [unused-ignore]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.16.0 (regression from 1.15.0)
• Mypy command-line flags: (see above)
• Mypy configuration options from mypy.ini (and other config files): (see above)
• Python version used: 3.13.1