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Warn about unused type: ignore comments when error code is disabled #18849

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Merged
merged 2 commits into from
Apr 3, 2025
Merged

Warn about unused type: ignore comments when error code is disabled #18849

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ba06eb5
Warn about unused `type: ignore` comments when error code is disabled
brianschubert Mar 28, 2025
73115d9
Add test cases for "type: ignore[unused-ignore]" interaction
brianschubert Mar 30, 2025
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9 changes: 6 additions & 3 deletions mypy/errors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -506,10 +506,13 @@ def add_error_info(self, info: ErrorInfo) -> None:
# line == end_line for most nodes, so we only loop once.
for scope_line in lines:
if self.is_ignored_error(scope_line, info, self.ignored_lines[file]):
err_code = info.code or codes.MISC
if not self.is_error_code_enabled(err_code):
# Error code is disabled - don't mark the current
# "type: ignore" comment as used.
return
# Annotation requests us to ignore all errors on this line.
self.used_ignored_lines[file][scope_line].append(
(info.code or codes.MISC).code
)
self.used_ignored_lines[file][scope_line].append(err_code.code)
return
if file in self.ignored_files:
return
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13 changes: 13 additions & 0 deletions test-data/unit/check-errorcodes.test
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Expand Up @@ -105,6 +105,19 @@ x # type: ignore[name-defined, attr-defined] # E: Unused "type: ignore[attr-defi
# flags: --warn-unused-ignores
"x" # type: ignore[name-defined] # E: Unused "type: ignore" comment [unused-ignore]

[case testErrorCodeWarnUnusedIgnores7_WarnWhenErrorCodeDisabled]
# flags: --warn-unused-ignores --disable-error-code name-defined
x # type: ignore # E: Unused "type: ignore" comment [unused-ignore]
x # type: ignore[name-defined] # E: Unused "type: ignore" comment [unused-ignore]
"x".foobar(y) # type: ignore[name-defined, attr-defined] # E: Unused "type: ignore[name-defined]" comment [unused-ignore]
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@hauntsaninja hauntsaninja Mar 29, 2025

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maybe also check interactions with # type: ignore[unused-ignore]?

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@brianschubert brianschubert Mar 30, 2025

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Added some tests! The behavior seems to be what we'd want - adding # type: ignore[unused-ignore] suppresses any unused-ignore warnings. There's no way to make mypy warn about an unused # type: ignore[unused-ignore], but I don't think that's a problem?


[case testErrorCodeWarnUnusedIgnores8_IgnoreUnusedIgnore]
# flags: --warn-unused-ignores --disable-error-code name-defined
"x" # type: ignore[unused-ignore]
"x" # type: ignore[name-defined, unused-ignore]
"x" # type: ignore[xyz, unused-ignore]
x # type: ignore[name-defined, unused-ignore]

[case testErrorCodeMissingWhenRequired]
# flags: --enable-error-code ignore-without-code
"x" # type: ignore # E: "type: ignore" comment without error code [ignore-without-code]
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