Re-work colcon_core.command.get_prog_name (#617)

This function's purpose is to handle these special cases of argv[0]:
* Invoked using python -m ...
* Invoked using a path to the executable even though the executable is
   on the PATH

This change enhances the path comparison to support normalization of
that path, Windows long path prefixes, and also the easy-install
behavior on Windows where argv[0] has no extension.

Yet to be properly handled is invocation using python -c ...

colcon_core/command.py

@@ -275,9 +275,28 @@ def get_prog_name():
     if basename == '__main__.py':
         # use the module name in case the script was invoked with python -m ...
         prog = os.path.basename(os.path.dirname(prog))
-    elif shutil.which(basename) == prog:
-        # use basename only if it is on the PATH
-        prog = basename
+    else:
+        default_prog = shutil.which(basename) or ''
+        default_ext = os.path.splitext(default_prog)[1]
+        real_prog = prog
+        if (
+            sys.platform == 'win32' and
+            os.path.splitext(real_prog)[1] != default_ext
+        ):
+            # On Windows, setuptools entry points drop the file extension from
+            # argv[0], but shutil.which does not. If the two don't end in the
+            # same extension, try appending the shutil extension for a better
+            # chance at matching.
+            real_prog += default_ext
+        try:
+            # The os.path.samefile requires that both files exist on disk, but
+            # has the advantage of working around symlinks, UNC-style paths,
+            # DOS 8.3 path atoms, and path normalization.
+            if os.path.samefile(default_prog, real_prog):
+                # use basename only if it is on the PATH
+                prog = basename
+        except (FileNotFoundError, NotADirectoryError):
+            pass
     return prog
 
 

test/spell_check.words

@@ -116,6 +116,7 @@ setuptools
 shlex
 sigint
 sitecustomize
+skipif
 sloretz
 stacklevel
 staticmethod

test/test_command.py

@@ -1,15 +1,18 @@
 # Copyright 2016-2018 Dirk Thomas
 # Licensed under the Apache License, Version 2.0
 
+import os
 import shutil
 import signal
 import sys
 from tempfile import mkdtemp
+from tempfile import TemporaryDirectory
 from unittest.mock import Mock
 from unittest.mock import patch
 
 from colcon_core.command import CommandContext
 from colcon_core.command import create_parser
+from colcon_core.command import get_prog_name
 from colcon_core.command import main
 from colcon_core.command import verb_main
 from colcon_core.environment_variable import EnvironmentVariable
@@ -151,3 +154,86 @@ def test_verb_main():
     assert logger.error.call_args[0][0].startswith(
         'command_name verb_name: custom error message\n')
     assert 'Exception: custom error message' in logger.error.call_args[0][0]
+
+
+def test_prog_name_module():
+    argv = [os.path.join('foo', 'bar', '__main__.py')]
+    with patch('colcon_core.command.sys.argv', argv):
+        # prog should be the module containing __main__.py
+        assert get_prog_name() == 'bar'
+
+
+def test_prog_name_on_path():
+    # use __file__ since we know it exists
+    argv = [__file__]
+    with patch('colcon_core.command.sys.argv', argv):
+        with patch(
+            'colcon_core.command.shutil.which',
+            return_value=__file__
+        ):
+            # prog should be shortened to the basename
+            assert get_prog_name() == 'test_command.py'
+
+
+def test_prog_name_not_on_path():
+    # use __file__ since we know it exists
+    argv = [__file__]
+    with patch('colcon_core.command.sys.argv', argv):
+        with patch('colcon_core.command.shutil.which', return_value=None):
+            # prog should remain unchanged
+            assert get_prog_name() == __file__
+
+
+def test_prog_name_different_on_path():
+    # use __file__ since we know it exists
+    argv = [__file__]
+    with patch('colcon_core.command.sys.argv', argv):
+        with patch(
+            'colcon_core.command.shutil.which',
+            return_value=sys.executable
+        ):
+            # prog should remain unchanged
+            assert get_prog_name() == __file__
+
+
+def test_prog_name_not_a_file():
+    # pick some file that doesn't actually exist on disk
+    no_such_file = os.path.join(__file__, 'foobar')
+    argv = [no_such_file]
+    with patch('colcon_core.command.sys.argv', argv):
+        with patch(
+            'colcon_core.command.shutil.which',
+            return_value=no_such_file
+        ):
+            # prog should remain unchanged
+            assert get_prog_name() == no_such_file
+
+
+@pytest.mark.skipif(sys.platform == 'win32', reason='Symlinks not supported.')
+def test_prog_name_symlink():
+    # use __file__ since we know it exists
+    with TemporaryDirectory(prefix='test_colcon_') as temp_dir:
+        linked_file = os.path.join(temp_dir, 'test_command.py')
+        os.symlink(__file__, linked_file)
+
+        argv = [linked_file]
+        with patch('colcon_core.command.sys.argv', argv):
+            with patch(
+                'colcon_core.command.shutil.which',
+                return_value=__file__
+            ):
+                # prog should be shortened to the basename
+                assert get_prog_name() == 'test_command.py'
+
+
+@pytest.mark.skipif(sys.platform != 'win32', reason='Only valid on Windows.')
+def test_prog_name_easy_install():
+    # use __file__ since we know it exists
+    argv = [__file__[:-3]]
+    with patch('colcon_core.command.sys.argv', argv):
+        with patch(
+            'colcon_core.command.shutil.which',
+            return_value=__file__
+        ):
+            # prog should be shortened to the basename
+            assert get_prog_name() == 'test_command'