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Catch TypeVisitor subclasses with unimplemented abstract methods #730

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#7312
Closed
Catch TypeVisitor subclasses with unimplemented abstract methods#730
#7312
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bugmypy got something wrongfalse-positivemypy gave an error on correct codepriority-1-normal

Description

@JamesGuthrie
JamesGuthrie
opened on Jul 27, 2015

Issue #638 was a pain to find because the root cause is an unimplemented abstract method which silently returns None and somewhere down the line causes type checking to fail. It would be better to check this explicitly. The following shows that this is done for one of the abstract methods:
https://github.com/JukkaL/mypy/blob/bbb2dd4f07f995a4b28b8044fa91aa97960fe192/mypy/types.py#L532. There are two potential solutions: 1) use abc's @AbstractMethod decorator, 2) raise an error directly in TypeVisitor.

  1. Ensures that future implementations and changes catch subclasses which do not implement the abstract methods, but requires adding implementations for all of the abstract methods to existing subclasses which are missing them. As there are a few, it would probably be simplest to raise an error there instead of providing the complete implementation, which raises the question: why not just use 2) straight off the bat?

@JukkaL Do you have a preferred solution?

Activity

  1. o11c commented on Jul 27, 2015

    @o11c
    o11c
    on Jul 27, 2015
    Contributor

    I am suspicious of any visitors that can meaningfully work without full implementations.

    Perhaps there is a need for more specific visitors?

  2. JamesGuthrie commented on Jul 28, 2015

    @JamesGuthrie
    JamesGuthrie
    on Jul 28, 2015
    ContributorAuthor

    It appears as though there is a common pattern of unimplemented abstract methods (visit_star_type, visit_overloaded, visit_error_type, visit_erased_type), I figured that maybe they had been added after the initial implementation of all visitors, and don't appear in the test cases and as such haven't been caught. In total there are about 25 subclasses which do not implement all abstract methods, mostly it is either visit_star_type or visit_overloaded which are unimplemented.

  3. JukkaL
    added
    bugmypy got something wrong
    on Aug 4, 2015

  4. JukkaL commented on Aug 4, 2015

    @JukkaL
    JukkaL
    on Aug 4, 2015
    Collaborator

    The current implementation is just sloppy, and is inherited from early pre-mypy days when there were no abstract methods.

    Using @abstractmethod is probably the best option, as missing implementations can then be caught statically. Trying to catch all of these errors using test cases is an uphill battle.

  5. JamesGuthrie
    added a commit that references this issue on Aug 4, 2015

    Catch incomplete TypeVisitor implementations

    9df3a84

  6. JamesGuthrie commented on Aug 4, 2015

    @JamesGuthrie
    JamesGuthrie
    on Aug 4, 2015
    ContributorAuthor

    I've opened a PR to get the ball rolling.

    As mentioned in the PR, Subclasses with incomplete implementations are:

    EraseTypeVisitor (mypy/erasetype.py: 26)
    visit_ellipsis_type()
    visit_star_type()

SameTypeVisitor(mypy/sametype.py: 29)
    visit_overloaded()
    visit_ellipsis_type()
    visit_star_type()

ExpandTypeVisitor(mypy/expandtype.py: 35)
    visit_ellipsis_type()
    visit_star_type()

SubtypeVisitor(mypy/subtypes.py: 44)
    visit_ellipsis_type()
    visit_star_type()

TypeAnalyser(mypy/typeanal.py: 58)
    visit_error_type()
    visit_overloaded()
    visit_ellipsis_type()
    visit_star_type()

TypeJoinVisitor(mypy/join.py: 70)
    visit_overloaded()
    visit_ellipsis_type()
    visit_star_type()

TypeMeetVisitor(mypy/meet.py: 77)
    visit_ellipsis_type()
    visit_star_type()

ConstraintBuilderVisitor(mypy/constraints.py: 125)
    visit_error_type()
    visit_overloaded()
    visit_ellipsis_type()
    visit_star_type()
    visit_type_list()

TypeQuery(mypy/types.py: 760)
    visit_overloaded()
    visit_ellipsis_type()

subclasses of TypeQuery:
    HasAnyQuery(mypy/stats.py: 223)
    HasAnyQuery2(mypy/stats.py: 241)
    ArgInferSecondpassQuery(mypy/checkexpr.py: 1375)
    HasTypeVarQuery(mypy/checkexpr.py: 1389)
    HasErasedComponentsQuery(mypy/checkexpr.py: 1402)

TypeAnalyserPass3(mypy/typeanal.py: 234)
    visit_error_type()
    visit_overloaded()
    visit_ellipsis_type()
    visit_star_type()
    visit_type_list()
  7. JamesGuthrie
    added 9 commits that reference this issue on Aug 24, 2015

    Catch incomplete TypeVisitor implementations

    1f83def

    Raise error on unimplemented abstract method call

    9225437

    Add SameTypeVisitor.visit_overloaded() implementation

    f4c5a97

    Add visit_overloaded() to TypeVisitor.

    89e5c04

    Add visit_overloaded to TypeQuery

    d8ef5f0

    add visit_star_type to TypeAnalyserPass3

    8cbf4d2

    add visit_overloaded to ConstraintBuilderVisitor

    b3bb5c2

    Add SameTypeVisitor.visit_overloaded() implementation

    93c2b80

    Add visit_overloaded() to TypeTranslator.

    b2af6f4

  8. 13 remaining items

  9. JukkaL
    added 5 commits that reference this issue on Oct 17, 2015

    Add SameTypeVisitor.visit_overloaded() implementation

    93f096d

    Add visit_overloaded() to TypeTranslator.

    d86fc75

    Add visit_overloaded() to TypeQuery

    da7080f

    add visit_star_type() to TypeAnalyserPass3

    dc941e5

    add visit_overloaded() to ConstraintBuilderVisitor

    15e2156
  10. sixolet
    added a commit that references this issue on Apr 20, 2017

    Use inheritance to allow most TypeVisitors not to deal with "syntheti…

    8f7d5c7
  11. JukkaL
    added a commit that references this issue on Apr 20, 2017

    Use inheritance to allow most TypeVisitors not to deal with "syntheti…

    dde184f

  12. jbsiddall commented on Apr 13, 2018

    @jbsiddall
    jbsiddall
    on Apr 13, 2018

    Is there any update on this? mypy 0.580 is stil showing this error for code: for item in {int}: pass

  13. JelleZijlstra commented on Apr 13, 2018

    @JelleZijlstra
    JelleZijlstra
    on Apr 13, 2018
    Member

    Are you sure you're on the right issue? This one is talking about an internal problem in mypy as far as I can tell.

  14. JukkaL
    added
    priority-1-normal
    false-positivemypy gave an error on correct code
    on May 17, 2018
  15. Michael0x2a
    added a commit that references this issue on Aug 10, 2019

    Make TypeVisitor and SyntheticTypeVisitor fully abstract

    2a550d8
  16. ilevkivskyi
    closed this as completedin #7312on Aug 22, 2019
  17. ilevkivskyi
    added a commit that references this issue on Aug 22, 2019

    Make TypeVisitor and SyntheticTypeVisitor (almost) fully abstract (#7312

    5ebd05e
  18. Michael0x2a
    added a commit that references this issue on Aug 25, 2019

    Make TypeVisitor and SyntheticTypeVisitor (almost) fully abstract (py…

    42dc938
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