Lint explicit files even when excluded

src/flake8/api/legacy.py

@@ -10,7 +10,7 @@ import logging
 import os.path
 from typing import Any
 
-from flake8.discover_files import expand_paths
+from flake8 import utils
 from flake8.formatting import base as formatter
 from flake8.main import application as app
 from flake8.options.parse_args import parse_args
@@ -129,15 +129,12 @@ class StyleGuide:
         """
 
         def excluded(path: str) -> bool:
-            paths = tuple(
-                expand_paths(
-                    paths=[path],
-                    stdin_display_name=self.options.stdin_display_name,
-                    filename_patterns=self.options.filename,
-                    exclude=self.options.exclude,
-                ),
+            return utils.matches_filename(
+                path,
+                patterns=self.options.exclude,
+                log_message='"%(path)s" has %(whether)sbeen excluded',
+                logger=LOG,
             )
-            return not paths
 
         return excluded(filename) or (
             parent is not None and excluded(os.path.join(parent, filename))

src/flake8/discover_files.py

@@ -22,17 +22,19 @@ def _filenames_from(
     :param arg:
         Parameter from the command-line.
     :param predicate:
-        Predicate to use to filter out filenames. If the predicate
-        returns ``True`` we will exclude the filename, otherwise we
-        will yield it. By default, we include every filename
-        generated.
+        Predicate to use to filter out paths discovered from directories
+        or stdin aliases. Direct file arguments are yielded even if the
+        predicate matches them.
     :returns:
         Generator of paths
     """
-    if predicate(arg):
+    if arg == "-" and predicate(arg):
         return
 
     if os.path.isdir(arg):
+        if predicate(arg):
+            return
+
         for root, sub_directories, files in os.walk(arg):
             # NOTE(sigmavirus24): os.walk() will skip a directory if you
             # remove it from the list of sub-directories.

tests/integration/test_main.py

@@ -135,6 +135,20 @@ def test_extend_exclude(tmpdir, capsys):
     assert err == ""
 
 
+def test_explicit_file_ignores_exclude(tmpdir, capsys):
+    tmpdir.join("test/module.py").ensure()
+    tmpdir.join("test/module.py").write("import os\n")
+    tmpdir.join(".flake8").write("[flake8]\nexclude = module.py\n")
+
+    with tmpdir.as_cwd():
+        assert cli.main(["test/module.py"]) == 1
+
+    expected_out = "test/module.py:1:1: F401 'os' imported but unused\n"
+    out, err = capsys.readouterr()
+    assert out == expected_out.replace("/", os.sep)
+    assert err == ""
+
+
 def test_malformed_per_file_ignores_error(tmpdir, capsys):
     """Test the error message for malformed `per-file-ignores`."""
     setup_cfg = """\

tests/unit/test_discover_files.py

@@ -95,11 +95,11 @@ def test_filenames_from_exclude_doesnt_exclude_directory_names(tmpdir):
     assert filenames == [os.path.join(".", "2", "1", "return_me.py")]
 
 
-def test_filenames_from_predicate_applies_to_initial_arg(tmp_path):
-    """Test that the predicate is also applied to the passed argument."""
+def test_filenames_from_predicate_does_not_apply_to_initial_file(tmp_path):
+    """Test that the predicate is not applied to a directly passed file."""
     fname = str(tmp_path.joinpath("f.py"))
     ret = tuple(_filenames_from(fname, predicate=lambda _: True))
-    assert ret == ()
+    assert ret == (fname,)
 
 
 def test_filenames_from_predicate_applies_to_dirname(tmp_path):
@@ -164,3 +164,10 @@ def test_alternate_stdin_name_is_filtered():
 def test_filename_included_even_if_not_matching_include(tmp_path):
     some_file = str(tmp_path.joinpath("some/file"))
     assert _expand_paths(paths=(some_file,)) == {some_file}
+
+
+def test_filename_included_even_if_matching_exclude(tmp_path):
+    some_file = str(tmp_path.joinpath("some/file.py"))
+    assert _expand_paths(paths=(some_file,), exclude=("file.py",)) == {
+        some_file,
+    }