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[red-knot] Panics on generic type alias #14307

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Tracked by #13478
sharkdp opened this issue Nov 13, 2024 · 1 comment · Fixed by #14312
Closed
Tracked by #13478

[red-knot] Panics on generic type alias #14307

sharkdp opened this issue Nov 13, 2024 · 1 comment · Fixed by #14312
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bug Something isn't working red-knot Multi-file analysis & type inference

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sharkdp commented Nov 13, 2024

Red knot currently panics when encountering PEP-695 generic type aliases:

type ListOrSet[T] = list[T] | set[T]

Backtrace:

thread '<unnamed>' panicked at crates/red_knot_python_semantic/src/types/infer.rs:872:37:
no entry found for key
stack backtrace:
[…]
   6: red_knot_python_semantic::semantic_index::SemanticIndex::definition
             at ./crates/red_knot_python_semantic/src/semantic_index.rs:210:33
   7: red_knot_python_semantic::types::infer::TypeInferenceBuilder::infer_definition
             at ./crates/red_knot_python_semantic/src/types/infer.rs:872:26
   8: red_knot_python_semantic::types::infer::TypeInferenceBuilder::infer_type_parameters
             at ./crates/red_knot_python_semantic/src/types/infer.rs:4036:50
   9: red_knot_python_semantic::types::infer::TypeInferenceBuilder::infer_type_alias_statement
             at ./crates/red_knot_python_semantic/src/types/infer.rs:1805:13
  10: red_knot_python_semantic::types::infer::TypeInferenceBuilder::infer_statement
             at ./crates/red_knot_python_semantic/src/types/infer.rs:851:53
  11: red_knot_python_semantic::types::infer::TypeInferenceBuilder::infer_body
             at ./crates/red_knot_python_semantic/src/types/infer.rs:831:13
  12: red_knot_python_semantic::types::infer::TypeInferenceBuilder::infer_module
             at ./crates/red_knot_python_semantic/src/types/infer.rs:793:9
  13: red_knot_python_semantic::types::infer::TypeInferenceBuilder::infer_region_scope
             at ./crates/red_knot_python_semantic/src/types/infer.rs:417:17
  14: red_knot_python_semantic::types::infer::TypeInferenceBuilder::infer_region
             at ./crates/red_knot_python_semantic/src/types/infer.rs:405:46
  15: red_knot_python_semantic::types::infer::TypeInferenceBuilder::finish
             at ./crates/red_knot_python_semantic/src/types/infer.rs:4044:9
@sharkdp sharkdp added the red-knot Multi-file analysis & type inference label Nov 13, 2024
@sharkdp sharkdp self-assigned this Nov 13, 2024
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sharkdp commented Nov 13, 2024 •
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Fixing this probably involves understanding type … = … statements as having their own annotation scope (https://docs.python.org/3/reference/compound_stmts.html#generic-type-aliases).

@sharkdp sharkdp mentioned this issue Nov 13, 2024
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@sharkdp sharkdp added the bug Something isn't working label Nov 13, 2024
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sharkdp added a commit that referenced this issue Nov 13, 2024
@sharkdp
[red-knot] Avoid panic for generic type aliases (#14312)
0eb36e4 
## Summary

This avoids a panic inside `TypeInferenceBuilder::infer_type_parameters`
when encountering generic type aliases:
```py
type ListOrSet[T] = list[T] | set[T]
```

To fix this properly, we would have to treat type aliases as being their own
annotation scope [1]. The left hand side is a definition for the type parameter
`T` which is being used in the special annotation scope on the right hand side.
Similar to how it works for generic functions and classes.

[1] https://docs.python.org/3/reference/compound_stmts.html#generic-type-aliases


closes #14307

## Test Plan

Added new example to the corpus.
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[red-knot] Avoid panic for generic type aliases astral-sh/ruff
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