Dataflow analysis #313

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1. MikhailArkhipov commented on Jun 3, 2019

   

   Mikhail Arkhipov (MikhailArkhipov)

   on Jun 3, 2019

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   New LS no longer collects combinations of types. In the example above a will be just bool.
2. Mikhail Arkhipov (MikhailArkhipov)

   closed this as completedon Jun 3, 2019
3. lostmsu commented on Jun 3, 2019

   

   Victor (lostmsu)

   on Jun 3, 2019

   Last edited by lostmsu

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   Mikhail Arkhipov (@MikhailArkhipov) out of curiosity: what would the new LS say about a in

   if condition():
     a = "1"
   else:
     a = [1]
4. jakebailey commented on Jun 3, 2019

   

   Jake Bailey (jakebailey)

   on Jun 3, 2019

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   In that example, list, because we take the final assign:

   

   You couldn't represent that code within the python typing world.

   However, we do handle something like this:

   
5. lostmsu commented on Jun 3, 2019

   

   Victor (lostmsu)

   on Jun 3, 2019

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   Jake Bailey (@jakebailey) why not? What is the difference between b and a in this case? Why can't a be Union[str, list]?
6. jakebailey commented on Jun 3, 2019

   

   Jake Bailey (jakebailey)

   on Jun 3, 2019

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   I overstated; you're right, we could potentially merge those multiple assigns (without dataflow analysis). The returns work because we can find every type returned and do the union then (which is less complicated).
7. lostmsu commented on Jun 3, 2019

   

   Victor (lostmsu)

   on Jun 3, 2019

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   Jake Bailey (@jakebailey) the older analysis would collect types from both branches. So that later it could strengthen the union as in Union[XDerivedFromBase, YDerivedFromBase] -> Base. Is this now completely ignored within a single function body?
8. jakebailey commented on Jun 3, 2019

   

   Jake Bailey (jakebailey)

   on Jun 3, 2019

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   Currently, the new analysis doesn't do any sort of unioning or strengthening at all, other than the return type case I gave above. You can specify the type using a type annotation (so, say that something is Base explicitly), but we currently don't do anything special to handle multiple assignments over variables besides normal scoping rules.
9. MikhailArkhipov commented on Jun 3, 2019

   

   Mikhail Arkhipov (MikhailArkhipov)

   on Jun 3, 2019

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   Analysis no longer collects unions of possible combinations of values for performance and memory consumption reasons. Similarly, it no longer collects or stores all possible function return types with various arguments.