stubgen: wrong import statements for base module when importing submodule

[patrick-kidger]

There's a bug with the import statements generated in .pyi files.

Consider the folder structure:

somefolder/
    test.py
    foo_mod/
        __init__.py
        bar_mod.py

with file contents:

# test.py
import foo_mod
import foo_mod.bar_mod as bar_mod

class baz(foo_mod.foo, bar_mod.bar):
    pass

# foo_mod/__init__.py
class foo:
    pass

# foo_mod/bar_mod.py
class bar:
    pass

Then running stubgen test.py whilst in somefolder generates an out/test.pyi file with contents:

# out/test.pyi
# Stubs for test (Python 3)
#
# NOTE: This dynamically typed stub was automatically generated by stubgen.

import foo_mod.bar_mod as bar_mod
import foo_mod.bar_mod

class baz(foo_mod.foo, bar_mod.bar): ...

Note how it says foo_mod.bar_mod, rather than just foo_mod as expected.

This issue generalises to subsubpackages as well (and presumably further). That is,

# test.py
import foo_mod
import foo_mod.bar_mod as bar_mod
import foo_mod.bar_mod.quux_mod as quux_mod
...

generates

# out/test.pyi
import foo_mod.bar_mod.quux_mod as bar_mod
import foo_mod.bar_mod.quux_mod
import foo_mod.bar_mod.quux_mod as quux_mod
...

Tested on Windows and Unix, with both mypy version 0.701 and the latest on the GitHub master branch, with Python 3.6.6. (At least, that's the version of Python which is bound to python on the command line, so presumably that's what stubgen is using?)

Possibly related? #6831

[patrick-kidger]

It seems that it's whichever import statement is last that is used. e.g.

# test.py
import foo_mod.bar_mod as bar_mod
import foo_mod
...

generates

# out/test.pyi
import foo_mod as bar_mod
import foo_mod
...

[ilevkivskyi]

I think this is a separate issue from #6831.