StdoutRefactoringTool sets files attribute even when no files need to be modified

[mahmoud]

Description

Hi there! While trying to enforce 2/3 compatibility on a large codebase, I ran across an issue with modernize's --enforce flag:

$ python-modernize --future-unicode --enforce enqueue_function.py
 Loading the following fixers:
    fissix.fixes.fix_apply  (apply)
    fissix.fixes.fix_except  (except)
    fissix.fixes.fix_exec  (exec)
    fissix.fixes.fix_execfile  (execfile)
    fissix.fixes.fix_exitfunc  (exitfunc)
    fissix.fixes.fix_funcattrs  (funcattrs)
    fissix.fixes.fix_has_key  (has_key)
    fissix.fixes.fix_idioms  (idioms)
    fissix.fixes.fix_long  (long)
    fissix.fixes.fix_methodattrs  (methodattrs)
    fissix.fixes.fix_ne  (ne)
    fissix.fixes.fix_numliterals  (numliterals)
    fissix.fixes.fix_operator  (operator)
    fissix.fixes.fix_paren  (paren)
    fissix.fixes.fix_reduce  (reduce)
    fissix.fixes.fix_renames  (renames)
    fissix.fixes.fix_repr  (repr)
    fissix.fixes.fix_set_literal  (set_literal)
    fissix.fixes.fix_standarderror  (standarderror)
    fissix.fixes.fix_sys_exc  (sys_exc)
    fissix.fixes.fix_throw  (throw)
    fissix.fixes.fix_tuple_params  (tuple_params)
    fissix.fixes.fix_types  (types)
    fissix.fixes.fix_ws_comma  (ws_comma)
    fissix.fixes.fix_xreadlines  (xreadlines)
    libmodernize.fixes.fix_basestring  (basestring)
    libmodernize.fixes.fix_dict_six  (dict_six)
    libmodernize.fixes.fix_file  (file)
    libmodernize.fixes.fix_filter  (filter)
    libmodernize.fixes.fix_import  (import)
    libmodernize.fixes.fix_imports_six  (imports_six)
    libmodernize.fixes.fix_input_six  (input_six)
    libmodernize.fixes.fix_int_long_tuple  (int_long_tuple)
    libmodernize.fixes.fix_itertools_imports_six  (itertools_imports_six)
    libmodernize.fixes.fix_itertools_six  (itertools_six)
    libmodernize.fixes.fix_map  (map)
    libmodernize.fixes.fix_metaclass  (metaclass)
    libmodernize.fixes.fix_next  (next)
    libmodernize.fixes.fix_print  (print)
    libmodernize.fixes.fix_raise  (raise)
    libmodernize.fixes.fix_raise_six  (raise_six)
    libmodernize.fixes.fix_unichr  (unichr)
    libmodernize.fixes.fix_unicode_future  (unicode_future)
    libmodernize.fixes.fix_unicode_type  (unicode_type)
    libmodernize.fixes.fix_urllib_six  (urllib_six)
    libmodernize.fixes.fix_xrange_six  (xrange_six)
    libmodernize.fixes.fix_zip  (zip)
 Applying the following explicit transformations:
    (None)

RefactoringTool: Skipping optional fixer: idioms
RefactoringTool: Skipping optional fixer: set_literal
RefactoringTool: Skipping optional fixer: ws_comma
RefactoringTool: No changes to ebill/ebill/tasks/enqueue_function.py
RefactoringTool: Files that need to be modified:
RefactoringTool: ebill/ebill/tasks/enqueue_function.py

As you can see in the last 3 lines, "no changes" but also "need to be modified". Seems like this is a longstanding issue with 2to3.

I think the "need to be modified" is translated into the rt.files attribute that powers the --enforce flag.

I haven't dug into fissix yet, but maybe it represents a suitable layer at which to undo the damage? If a path says "no changes", remove it from the files list? Just an idea!

Details

• OS: Ubuntu 18.04
• Python version: 3.6.9
• fissix version: 20.8.0
• Can you repro on master? yes
• Can you repro in a clean virtualenv? yes