Support type aliases in fine-grained incremental mode #4394

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1. JukkaL

   added

   topic-fine-grained-incremental

   on Dec 19, 2017
2. msullivan commented on Jan 17, 2018

   

   msullivan

   on Jan 17, 2018

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   Here is a test case for it that fails:

   [case testAliasUpdate]
   import b
   [file a.py]
   N = int
   x = 1
   [file a.py.2]
   N = str
   x = 'hi'
   [file b.py]
   import a
   def f(x: a.N) -> None:
       pass
   f(a.x)
   [out]
   ==
   
3. JukkaL

   added

   priority-0-high

   needs discussion

   on Jan 19, 2018
4. JukkaL commented on Jan 26, 2018

   

   JukkaL

   on Jan 26, 2018

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   The challenge here is that type aliases are completely replaced during semantic analysis, and thus we can't easily determine which type aliases were used after the fact. Here are two approaches for resolving this:

   1. Create a new type for type alias references that doesn't get simplified away during semantic analysis.
   2. Collect all expanded type aliases during semantic analysis and store them so that they can be used in dependency generation. For example, collect a dictionary from target to set of type aliases used.

   The first approach would likely require pretty major changes to mypy, since each Type object might need to be dereferenced to get the actual effective type. I prefer the second approach due to its simplicity, though it's a little hacky.
5. ilevkivskyi commented on Jan 26, 2018

   

   ilevkivskyi

   on Jan 26, 2018

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   There is a related issue #4082, but I think these two are independent. The other issue is about having it clear in the symbol table (not via type_override and other hacks), but the question about what to do about expanded types is different. I agree that option 2 is a bit hacky, but we did conceptually similar thing for forward references and it seems to work well. So I am fine with option 2 (also it is easy to implement).
6. ilevkivskyi

   self-assigned this

   on Jan 26, 2018
7. ilevkivskyi

   closed this as completedin #4525on Feb 21, 2018
8. ilevkivskyi

   added a commit that references this issue on Feb 21, 2018

   Support type aliases in fine-grained incremental mode (#4525)

   ...

   This issue will close once commit 8f253c2 is merged into the 'master' branch.

   8f253c2
9. yedpodtrzitko

   added a commit that references this issue on Mar 15, 2018

   Support type aliases in fine-grained incremental mode (python#4525)

   ...

   This issue will close once commit 5600ae8 is merged into the 'master' branch.

   5600ae8