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Clean-up type variable scope and binding #4814

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ilevkivskyi opened this issue Mar 28, 2018 · 3 comments
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Clean-up type variable scope and binding #4814

ilevkivskyi opened this issue Mar 28, 2018 · 3 comments
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meta Issues tracking a broad area of work priority-1-normal refactoring Changing mypy's internals semantic-analyzer Problems that happen during semantic analysis

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@ilevkivskyi
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Currently the code around type variable binding in functions is a bit unclear and does some strange things like binding typer variables before function type is analyzed and depending on TypeVarQuery returning short (unqualified) names.
@ilevkivskyi ilevkivskyi added refactoring Changing mypy's internals priority-1-normal labels Mar 28, 2018
@ilevkivskyi
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Another related comment here is that we have a bit too many "things" related to type variables (in addition to TypeVarScope mentioned above):

  • TypeVarExpr
  • TypeVarDef
  • TypeVarType
  • TypeVarId
    We can probably simplify a bit the model of how type variables work.

@ilevkivskyi ilevkivskyi mentioned this issue Sep 1, 2018
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@ilevkivskyi
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Probably it makes sense to clean up (or at least document) various things related to type variable scopes while we are working on the new semantic analyzer. I just discovered an inconsistency in new analyzer, it was using full type variable name where short one was expected. Without documentation, such errors are easy to make.

@ilevkivskyi ilevkivskyi added the semantic-analyzer Problems that happen during semantic analysis label Feb 24, 2019
@ilevkivskyi ilevkivskyi self-assigned this Feb 24, 2019
@SKHecht SKHecht mentioned this issue Mar 12, 2019
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@ilevkivskyi ilevkivskyi removed their assignment Dec 9, 2019
@hauntsaninja hauntsaninja mentioned this issue Jan 24, 2021
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hauntsaninja added a commit that referenced this issue Aug 4, 2021
@hauntsaninja
Merge TypeVarDef and TypeVarType (#9951)
2736edb 
In the spirit of #4814 (comment)

I'm not sure what the distinction between TypeVarDef and TypeVarType was (note that there's also TypeVarExpr, whose purpose is clear to me).
In practice, it seems it boiled down to: a) TypeVarDef has a different __repr__, that's not user facing but was used in tests, b) in two places, we used the construction of a TypeVarType from a TypeVarDef as an opportunity to change the line number.

I ran into this because:
a) I was considering whether to create a corresponding ParamSpecDef and ParamSpecType
b) I was trying to fix an issue with applytype sometimes swallowing generics, which to fix I needed TypeVarType to have access to its TypeVarDef.
I was unable to find a reason for TypeVarType to not just be the TypeVarDef and here we are.

Co-authored-by: hauntsaninja <>
@ilevkivskyi ilevkivskyi mentioned this issue Aug 21, 2022
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@ilevkivskyi ilevkivskyi mentioned this issue Aug 28, 2022
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@ilevkivskyi ilevkivskyi added the meta Issues tracking a broad area of work label Aug 28, 2022
@ilevkivskyi
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FWIW I more happy now with how type variables work (e.g. we use namespaces everywhere). There still may be bugs, I think tvar_scope.py is somewhat over-complicated, but we can handle issues on one-by-one basis now.

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