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Michael0x2a opened this issue Jul 18, 2016 · 1 comment · Fixed by #1912
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Incremental mode crashes on #type: ignore comment on module when it was previously imported #1904

Michael0x2a opened this issue Jul 18, 2016 · 1 comment · Fixed by #1912

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@Michael0x2a
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Michael0x2a commented Jul 18, 2016 •
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Suppose you have the following two files:

a.py

import b  # type: ignore

b.py

# This file can be empty or non-empty

If you delete .mypy_cache then run mypy -i b.py a.py twice, you obtain the following error the second time you run mypy:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 184, in _run_module_as_main
    "__main__", mod_spec)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/Users/michaellee/Work/mypy/mypy/__main__.py", line 5, in <module>
    main(None)
  File "/Users/michaellee/Work/mypy/mypy/main.py", line 40, in main
    res = type_check_only(sources, bin_dir, options)
  File "/Users/michaellee/Work/mypy/mypy/main.py", line 81, in type_check_only
    options=options)
  File "/Users/michaellee/Work/mypy/mypy/build.py", line 178, in build
    dispatch(sources, manager)
  File "/Users/michaellee/Work/mypy/mypy/build.py", line 1339, in dispatch
    process_graph(graph, manager)
  File "/Users/michaellee/Work/mypy/mypy/build.py", line 1480, in process_graph
    process_fresh_scc(graph, scc)
  File "/Users/michaellee/Work/mypy/mypy/build.py", line 1539, in process_fresh_scc
    graph[id].fix_cross_refs()
  File "/Users/michaellee/Work/mypy/mypy/build.py", line 1202, in fix_cross_refs
    fixup_module_pass_one(self.tree, self.manager.modules)
  File "/Users/michaellee/Work/mypy/mypy/fixup.py", line 17, in fixup_module_pass_one
    node_fixer.visit_symbol_table(tree.names)
  File "/Users/michaellee/Work/mypy/mypy/fixup.py", line 75, in visit_symbol_table
    stnode = lookup_qualified_stnode(self.modules, cross_ref)
  File "/Users/michaellee/Work/mypy/mypy/fixup.py", line 237, in lookup_qualified_stnode
    assert '.' in head, "Cannot find %s" % (name,)
AssertionError: Cannot find b

However, just running mypy -i a.py twice or swapping the order of the files and running mypy -a a.py b.py appears to both work fine -- it appears that incremental mode does not behave correctly when it first parses a module normally then encounters it a second time when it's annotated with # type: ignore.
@Michael0x2a Michael0x2a changed the title Bad interaction with # type: ignore and incremental mode Incremental mode crashes on unnecessary #type: ignore comment on module import Jul 19, 2016
@Michael0x2a Michael0x2a changed the title Incremental mode crashes on unnecessary #type: ignore comment on module import Incremental mode crashes on #type: ignore comment on module when it was previously imported Jul 19, 2016
Michael0x2a pushed a commit to Michael0x2a/mypy that referenced this issue Jul 19, 2016
@MichaelLeeDBX
Make semantic analyzer mark ignored module imports
49d1ae5 
Previously, the semantic analyzer seemed to always mark import symbols as
being of kind MODULE_REF during the third pass and did not preserve
whether the module was previously marked with the `# type: ignore`
comment or not.

This caused a contradiction in some cases when mypy was run in incremental
mode: suppose file a.py imported file b.py, and marked that import with the
ignore annotation.

Since the import is being ignored, mypy would not register that import
as a dependency, but since the import (during the previous run) was
marked as a MODULE_REF, mypy would attempt to load that module anyways
in some cases.

This commit fixes python#1904.
@Michael0x2a Michael0x2a mentioned this issue Jul 19, 2016
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@gvanrossum gvanrossum mentioned this issue Jul 19, 2016
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@gvanrossum
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Could be caused by #1911?

@Michael0x2a Michael0x2a mentioned this issue Jul 19, 2016
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gvanrossum pushed a commit that referenced this issue Jul 19, 2016
@Michael0x2a @gvanrossum
Make mypy still check imports with # type: ignore comments if the i…
a0eadce 
…mport exists (#1912)

Fixes #1911; also incidentally fixes #1904.
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Make mypy still check imports with # type: ignore comments if the import exists Michael0x2a/mypy
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@Michael0x2a @gvanrossum