Non-idempotency with commented multiline imports

[dpoznik]

The following example illustrates a non-idempotency in isort==5.13.2:

from some.very.long.subpackage.path.defining.classes.to.be.imported import (
    SomeLengthyClassName1,  # noqa F401
    SomeLengthyClassName2,  # noqa F401
)

Running isort over this file changes it:

$ isort foo.py 
Fixing /path/to/foo.py
$ cat foo.py 
from some.very.long.subpackage.path.defining.classes.to.be.imported import (  # noqa F401
    SomeLengthyClassName1,
)
from some.very.long.subpackage.path.defining.classes.to.be.imported import (  # noqa F401
    SomeLengthyClassName2,
)

Then, running isort over the result changes it a second time:

$ isort foo.py 
Fixing /path/to/foo.py
$ cat foo.py 
from some.very.long.subpackage.path.defining.classes.to.be.imported import (  # noqa F401
    SomeLengthyClassName1,
    SomeLengthyClassName2,
)

I (and my editor) prefer the original version, as it enables applying the # noqa directives to individual imported objects, but the final version would be preferable to the intermediate version.

The following example illustrates some more unexpected behavior:

from some.very.long.subpackage.path.defining.classes.to.be.imported import (
    SomeLengthyClassName1,  # noqa F401
    SomeLengthyClassName2,
    SomeLengthyClassName3,  # noqa F401
)

Applying isort once results an in an unsorted file (SomeLengthyClassName3 before SomeLengthyClassName2):

$ isort foo.py 
Fixing /path/to/foo.py
$ cat foo.py 
from some.very.long.subpackage.path.defining.classes.to.be.imported import (  # noqa F401
    SomeLengthyClassName1,
)
from some.very.long.subpackage.path.defining.classes.to.be.imported import (  # noqa F401
    SomeLengthyClassName3,
)
from some.very.long.subpackage.path.defining.classes.to.be.imported import (
    SomeLengthyClassName2,
)

Then, applying isort a second time attaches a # noqa directive to an object that didn't have one in the original (i.e., SomeLengthyClassName2):

$ isort foo.py 
Fixing /path/to/foo.py
$ cat foo.py 
from some.very.long.subpackage.path.defining.classes.to.be.imported import (  # noqa F401
    SomeLengthyClassName1,
    SomeLengthyClassName2,
    SomeLengthyClassName3,
)