Fine-grained: Nested class causes extra triggers to fire

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
python
Domain
compilers, devtools

Research direction

Start in mypy/test/testfinegrained.py with testNestedClassLeakingFromMethod and reproduce the shown debug output. Trace how nested class names containing line numbers produce triggers for both old and new names. Done means the test no longer reports unnecessary triggers while preserving the incompatible-assignment error.

Written by the indexing model from the issue text.

Description

bug priority-2-low topic-fine-grained-incremental

This test case trigger too many triggers due to nested classes:

[case testNestedClassLeakingFromMethod]
import a

def f(o: a.A) -> None:
    o.b.x = 1

[file a.py]
class A:
    def f(self) -> None:
        class B:
            x: int
        self.b = B()

    def g(self) -> None:
        class B: pass
        self.c = B()

[file a.py.2]
class A:
    # extra line
    def f(self) -> None:
        class B:
            x: str
        self.b = B()

    def g(self) -> None:
        class B: pass
        self.c = B()
[out]
==
main:4: error: Incompatible types in assignment (expression has type "int", variable has type "str")

Here's the debug output:

mypy/test/testfinegrained.py ==== update 'a' ====
--- update single 'a' ---
triggered: ['<a.A.b>', '<a.A.c>', '<a.B@3>', '<a.B@4>', '<a.B@8>', '<a.B@9>']
process __main__.f
triggered: []

Note that since the line number is included in the class names, moving the class to another line changes the name and causes triggers for both the previous and new name to fire.

Not sure what's the best way to deal with this. If nested classes that leak from methods are rare enough this might not be a major problem.

Dominant language
Python
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