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ngnpope opened this issue Jun 5, 2025 · 1 comment · Fixed by #19247
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[1.16 regression] duplicated note for incompatible type #19240

ngnpope opened this issue Jun 5, 2025 · 1 comment · Fixed by #19247
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bug mypy got something wrong

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@ngnpope
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ngnpope commented Jun 5, 2025

Bug Report

Note lines are being repeated when an error for an incompatible type is raised in certain cases.

Encountered when adding support for mypy v1.16 in typeddjango/django-stubs#2703

Bisected to #18847

To Reproduce

from django.db import models


class MyModel(models.Model):
    char1 = models.CharField(max_length=200, choices="test")

Expected Behavior

$ uvx --python=3.12 --with=django-stubs mypy==1.15 --strict bug.py
Installed 9 packages in 71ms
bug.py:5: error: Need type annotation for "char1"  [var-annotated]
bug.py:5: error: Argument "choices" to "CharField" has incompatible type "str"; expected "Iterable[tuple[Any, Any] | tuple[str, Iterable[tuple[Any, Any]]]] | Mapping[Any, Any] | type[Choices] | Callable[[], Iterable[tuple[Any, Any] | tuple[str, Iterable[tuple[Any, Any]]]] | Mapping[Any, Any]] | None"  [arg-type]
bug.py:5: note: Following member(s) of "str" have conflicts:
bug.py:5: note:     Expected:
bug.py:5: note:         def __iter__(self) -> Iterator[tuple[Any, Any] | tuple[str, Iterable[tuple[Any, Any]]]]
bug.py:5: note:     Got:
bug.py:5: note:         def __iter__(self) -> Iterator[str]
Found 2 errors in 1 file (checked 1 source file)

Actual Behavior

$ uvx --with=django-stubs mypy==1.16 --strict bug.py
bug.py:5: error: Need type annotation for "char1"  [var-annotated]
bug.py:5: error: Argument "choices" to "CharField" has incompatible type "str"; expected "Iterable[tuple[Any, Any] | tuple[str, Iterable[tuple[Any, Any]]]] | Mapping[Any, Any] | type[Choices] | Callable[[], Iterable[tuple[Any, Any] | tuple[str, Iterable[tuple[Any, Any]]]] | Mapping[Any, Any]] | None"  [arg-type]
bug.py:5: note: Following member(s) of "str" have conflicts:
bug.py:5: note:     Expected:
bug.py:5: note:         def __iter__(self) -> Iterator[tuple[Any, Any] | tuple[str, Iterable[tuple[Any, Any]]]]
bug.py:5: note:     Got:
bug.py:5: note:         def __iter__(self) -> Iterator[str]
bug.py:5: note:     Expected:
bug.py:5: note:         def __iter__(self) -> Iterator[tuple[Any, Any] | tuple[str, Iterable[tuple[Any, Any]]]]
bug.py:5: note:     Got:
bug.py:5: note:         def __iter__(self) -> Iterator[str]
Found 2 errors in 1 file (checked 1 source file)

Note that the last four "note" lines are repeated.

Your Environment

  • Mypy version used: 1.16
  • Mypy command-line flags: --strict
  • Mypy configuration options from mypy.ini (and other config files): n/a
  • Python version used: Python 3.12
@ngnpope ngnpope added the bug mypy got something wrong label Jun 5, 2025
@ngnpope ngnpope mentioned this issue Jun 5, 2025
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@ilevkivskyi
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OK, I think I know what is going on:

  • First, as part of that PR we may visit r.h.s twice (which btw may be not really needed, so I may try to optimize it away).
  • Second, and probably more importantly, our logic for error de-duplication is flawed.

@hauntsaninja hauntsaninja mentioned this issue Jun 6, 2025
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@ilevkivskyi ilevkivskyi mentioned this issue Jun 7, 2025
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ilevkivskyi added a commit that referenced this issue Jun 10, 2025
@ilevkivskyi
Fix and simplify error de-duplication (#19247)
dc42e28 
Fixes #19240
Fixes #13517
Fixes #17791

Existing de-duplication logic is both complicated and fragile. By
specifying a `parent_error` for a note explicitly, we can do everything
in a more robust and simple way. In addition, this new argument makes
error code matching simpler.
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Fix and simplify error de-duplication ilevkivskyi/mypy
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