split out file discovery and test it

9 files changed, 291 insertions, 217 deletions

diff --git a/docs/source/internal/utils.rst b/docs/source/internal/utils.rst
index 387ec82..34b09f1 100644
--- a/docs/source/internal/utils.rst
+++ b/docs/source/internal/utils.rst
@@ -60,24 +60,6 @@ Another helpful function that is named only to be explicit given it is a very
 trivial check, this checks if the user specified ``-`` in their arguments to
 |Flake8| to indicate we should read from stdin.
 
-.. autofunction:: flake8.utils.filenames_from
-
-When provided an argument to |Flake8|, we need to be able to traverse
-directories in a convenient manner. For example, if someone runs
-
-.. code::
-
-    $ flake8 flake8/
-
-Then they want us to check all of the files in the directory ``flake8/``. This
-function will handle that while also handling the case where they specify a
-file like:
-
-.. code::
-
-    $ flake8 flake8/__init__.py
-
-
 .. autofunction:: flake8.utils.fnmatch
 
 The standard library's :func:`fnmatch.fnmatch` is excellent at deciding if a
diff --git a/setup.cfg b/setup.cfg
index fca70c6..1477769 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -111,6 +111,8 @@ warn_unused_ignores = true
 disallow_untyped_defs = true
 [mypy-flake8.defaults]
 disallow_untyped_defs = true
+[mypy-flake8.discover_files]
+disallow_untyped_defs = true
 [mypy-flake8.exceptions]
 disallow_untyped_defs = true
 [mypy-flake8.formatting.*]
diff --git a/src/flake8/checker.py b/src/flake8/checker.py
index cbff46f..dba5d08 100644
--- a/src/flake8/checker.py
+++ b/src/flake8/checker.py
@@ -15,6 +15,7 @@ from flake8 import defaults
 from flake8 import exceptions
 from flake8 import processor
 from flake8 import utils
+from flake8.discover_files import expand_paths
 
 Results = List[Tuple[str, int, int, str, Optional[str]]]
 
@@ -155,70 +156,21 @@ class Manager:
             )
         return reported_results_count
 
-    def is_path_excluded(self, path: str) -> bool:
-        """Check if a path is excluded.
-
-        :param str path:
-            Path to check against the exclude patterns.
-        :returns:
-            True if there are exclude patterns and the path matches,
-            otherwise False.
-        :rtype:
-            bool
-        """
-        if path == "-":
-            if self.options.stdin_display_name == "stdin":
-                return False
-            path = self.options.stdin_display_name
-
-        return utils.matches_filename(
-            path,
-            patterns=self.exclude,
-            log_message='"%(path)s" has %(whether)sbeen excluded',
-            logger=LOG,
-        )
-
     def make_checkers(self, paths: Optional[List[str]] = None) -> None:
         """Create checkers for each file."""
         if paths is None:
             paths = self.arguments
 
-        if not paths:
-            paths = ["."]
-
-        filename_patterns = self.options.filename
-        running_from_diff = self.options.diff
-
-        # NOTE(sigmavirus24): Yes this is a little unsightly, but it's our
-        # best solution right now.
-        def should_create_file_checker(filename, argument):
-            """Determine if we should create a file checker."""
-            matches_filename_patterns = utils.fnmatch(
-                filename, filename_patterns
-            )
-            is_stdin = filename == "-"
-            # NOTE(sigmavirus24): If a user explicitly specifies something,
-            # e.g, ``flake8 bin/script`` then we should run Flake8 against
-            # that. Since should_create_file_checker looks to see if the
-            # filename patterns match the filename, we want to skip that in
-            # the event that the argument and the filename are identical.
-            # If it was specified explicitly, the user intended for it to be
-            # checked.
-            explicitly_provided = not running_from_diff and (
-                argument == filename
-            )
-            return (
-                explicitly_provided or matches_filename_patterns
-            ) or is_stdin
-
         checks = self.checks.to_dictionary()
         self._all_checkers = [
             FileChecker(filename, checks, self.options)
-            for argument in paths
-            for filename in utils.filenames_from(
-                argument, self.is_path_excluded
+            for filename in expand_paths(
+                paths=paths,
+                stdin_display_name=self.options.stdin_display_name,
+                filename_patterns=self.options.filename,
+                exclude=self.exclude,
+                is_running_from_diff=self.options.diff,
             )
-            if should_create_file_checker(filename, argument)
         ]
         self.checkers = [c for c in self._all_checkers if c.should_process]
         LOG.info("Checking %d files", len(self.checkers))
diff --git a/src/flake8/discover_files.py b/src/flake8/discover_files.py
new file mode 100644
index 0000000..f51b9d0
--- /dev/null
+++ b/src/flake8/discover_files.py
@@ -0,0 +1,96 @@
+"""Functions related to discovering paths."""
+import logging
+import os.path
+from typing import Callable
+from typing import Generator
+from typing import Sequence
+
+from flake8 import utils
+
+LOG = logging.getLogger(__name__)
+
+
+def _filenames_from(
+    arg: str,
+    *,
+    predicate: Callable[[str], bool],
+) -> Generator[str, None, None]:
+    """Generate filenames from an argument.
+
+    :param str arg:
+        Parameter from the command-line.
+    :param callable 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.
+    :returns:
+        Generator of paths
+    """
+    if predicate(arg):
+        return
+
+    if os.path.isdir(arg):
+        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.
+            for directory in tuple(sub_directories):
+                joined = os.path.join(root, directory)
+                if predicate(joined):
+                    sub_directories.remove(directory)
+
+            for filename in files:
+                joined = os.path.join(root, filename)
+                if not predicate(joined):
+                    yield joined
+    else:
+        yield arg
+
+
+def expand_paths(
+    *,
+    paths: Sequence[str],
+    stdin_display_name: str,
+    filename_patterns: Sequence[str],
+    exclude: Sequence[str],
+    is_running_from_diff: bool,
+) -> Generator[str, None, None]:
+    """Expand out ``paths`` from commandline to the lintable files."""
+    if not paths:
+        paths = ["."]
+
+    def is_excluded(arg: str) -> bool:
+        if arg == "-":
+            # if the stdin_display_name is the default, always include it
+            if stdin_display_name == "stdin":
+                return False
+            arg = stdin_display_name
+
+        return utils.matches_filename(
+            arg,
+            patterns=exclude,
+            log_message='"%(path)s" has %(whether)sbeen excluded',
+            logger=LOG,
+        )
+
+    def is_included(arg: str, fname: str) -> bool:
+        # while running from a diff, the arguments aren't _explicitly_
+        # listed so we still filter them
+        if is_running_from_diff:
+            return utils.fnmatch(fname, filename_patterns)
+        else:
+            return (
+                # always lint `-`
+                fname == "-"
+                # always lint explicitly passed (even if not matching filter)
+                or arg == fname
+                # otherwise, check the file against filtered patterns
+                or utils.fnmatch(fname, filename_patterns)
+            )
+
+    return (
+        filename
+        for path in paths
+        for filename in _filenames_from(path, predicate=is_excluded)
+        if is_included(path, filename)
+    )
diff --git a/src/flake8/utils.py b/src/flake8/utils.py
index 4e68104..9eb2497 100644
--- a/src/flake8/utils.py
+++ b/src/flake8/utils.py
@@ -11,9 +11,7 @@ import re
 import sys
 import textwrap
 import tokenize
-from typing import Callable
 from typing import Dict
-from typing import Generator
 from typing import List
 from typing import Optional
 from typing import Pattern
@@ -294,52 +292,6 @@ def is_using_stdin(paths: List[str]) -> bool:
     return "-" in paths
 
 
-def _default_predicate(*args: str) -> bool:
-    return False
-
-
-def filenames_from(
-    arg: str, predicate: Optional[Callable[[str], bool]] = None
-) -> Generator[str, None, None]:
-    """Generate filenames from an argument.
-
-    :param str arg:
-        Parameter from the command-line.
-    :param callable 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.
-    :returns:
-        Generator of paths
-    """
-    if predicate is None:
-        predicate = _default_predicate
-
-    if predicate(arg):
-        return
-
-    if os.path.isdir(arg):
-        for root, sub_directories, files in os.walk(arg):
-            if predicate(root):
-                sub_directories[:] = []
-                continue
-
-            # NOTE(sigmavirus24): os.walk() will skip a directory if you
-            # remove it from the list of sub-directories.
-            for directory in sub_directories:
-                joined = os.path.join(root, directory)
-                if predicate(joined):
-                    sub_directories.remove(directory)
-
-            for filename in files:
-                joined = os.path.join(root, filename)
-                if not predicate(joined):
-                    yield joined
-    else:
-        yield arg
-
-
 def fnmatch(filename: str, patterns: Sequence[str]) -> bool:
     """Wrap :func:`fnmatch.fnmatch` to add some functionality.
 
@@ -351,7 +303,7 @@ def fnmatch(filename: str, patterns: Sequence[str]) -> bool:
         The default value if patterns is empty
     :returns:
         True if a pattern matches the filename, False if it doesn't.
-        ``default`` if patterns is empty.
+        ``True`` if patterns is empty.
     """
     if not patterns:
         return True
diff --git a/tests/unit/test_checker_manager.py b/tests/unit/test_checker_manager.py
index 8e45675..6594453 100644
--- a/tests/unit/test_checker_manager.py
+++ b/tests/unit/test_checker_manager.py
@@ -85,11 +85,9 @@ def test_make_checkers(_):
     }
     manager = checker.Manager(style_guide, files, checkplugins)
 
-    with mock.patch("flake8.utils.filenames_from") as filenames_from:
-        filenames_from.side_effect = [["file1"], ["file2"]]
-        with mock.patch("flake8.utils.fnmatch", return_value=True):
-            with mock.patch("flake8.processor.FileProcessor"):
-                manager.make_checkers()
+    with mock.patch("flake8.utils.fnmatch", return_value=True):
+        with mock.patch("flake8.processor.FileProcessor"):
+            manager.make_checkers(["file1", "file2"])
 
     assert manager._all_checkers
     for file_checker in manager._all_checkers:
diff --git a/tests/unit/test_discover_files.py b/tests/unit/test_discover_files.py
new file mode 100644
index 0000000..f2dfa13
--- /dev/null
+++ b/tests/unit/test_discover_files.py
@@ -0,0 +1,174 @@
+import os.path
+
+import pytest
+
+from flake8 import utils
+from flake8.discover_files import _filenames_from
+from flake8.discover_files import expand_paths
+
+
+@pytest.fixture
+def files_dir(tmpdir):
+    """Create test dir for testing filenames_from."""
+    with tmpdir.as_cwd():
+        tmpdir.join("a/b/c.py").ensure()
+        tmpdir.join("a/b/d.py").ensure()
+        tmpdir.join("a/b/e/f.py").ensure()
+        yield tmpdir
+
+
+def _noop(path):
+    return False
+
+
+def _normpath(s):
+    return s.replace("/", os.sep)
+
+
+def _normpaths(pths):
+    return {_normpath(pth) for pth in pths}
+
+
+@pytest.mark.usefixtures("files_dir")
+def test_filenames_from_a_directory():
+    """Verify that filenames_from walks a directory."""
+    filenames = set(_filenames_from(_normpath("a/b/"), predicate=_noop))
+    # should include all files
+    expected = _normpaths(("a/b/c.py", "a/b/d.py", "a/b/e/f.py"))
+    assert filenames == expected
+
+
+@pytest.mark.usefixtures("files_dir")
+def test_filenames_from_a_directory_with_a_predicate():
+    """Verify that predicates filter filenames_from."""
+    filenames = set(
+        _filenames_from(
+            arg=_normpath("a/b/"),
+            predicate=lambda path: path.endswith(_normpath("b/c.py")),
+        )
+    )
+    # should not include c.py
+    expected = _normpaths(("a/b/d.py", "a/b/e/f.py"))
+    assert filenames == expected
+
+
+@pytest.mark.usefixtures("files_dir")
+def test_filenames_from_a_directory_with_a_predicate_from_the_current_dir():
+    """Verify that predicates filter filenames_from."""
+    filenames = set(
+        _filenames_from(
+            arg=_normpath("./a/b"),
+            predicate=lambda path: path == "c.py",
+        )
+    )
+    # none should have matched the predicate so all returned
+    expected = _normpaths(("./a/b/c.py", "./a/b/d.py", "./a/b/e/f.py"))
+    assert filenames == expected
+
+
+@pytest.mark.usefixtures("files_dir")
+def test_filenames_from_a_single_file():
+    """Verify that we simply yield that filename."""
+    filenames = set(_filenames_from(_normpath("a/b/c.py"), predicate=_noop))
+    assert filenames == {_normpath("a/b/c.py")}
+
+
+def test_filenames_from_a_single_file_does_not_exist():
+    """Verify that a passed filename which does not exist is returned back."""
+    filenames = set(_filenames_from(_normpath("d/n/e.py"), predicate=_noop))
+    assert filenames == {_normpath("d/n/e.py")}
+
+
+def test_filenames_from_exclude_doesnt_exclude_directory_names(tmpdir):
+    """Verify that we don't greedily exclude subdirs."""
+    tmpdir.join("1/dont_return_me.py").ensure()
+    tmpdir.join("2/1/return_me.py").ensure()
+    exclude = [tmpdir.join("1").strpath]
+
+    def predicate(pth):
+        return utils.fnmatch(os.path.abspath(pth), exclude)
+
+    with tmpdir.as_cwd():
+        filenames = list(_filenames_from(".", predicate=predicate))
+    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."""
+    fname = str(tmp_path.joinpath("f.py"))
+    ret = tuple(_filenames_from(fname, predicate=lambda _: True))
+    assert ret == ()
+
+
+def test_filenames_from_predicate_applies_to_dirname(tmp_path):
+    """Test that the predicate can filter whole directories."""
+    a_dir = tmp_path.joinpath("a")
+    a_dir.mkdir()
+    a_dir.joinpath("b.py").touch()
+
+    b_py = tmp_path.joinpath("b.py")
+    b_py.touch()
+
+    def predicate(p):
+        # filter out the /a directory
+        return p.endswith("a")
+
+    ret = tuple(_filenames_from(str(tmp_path), predicate=predicate))
+    assert ret == (str(b_py),)
+
+
+def _expand_paths(
+    *,
+    paths=(".",),
+    stdin_display_name="stdin",
+    filename_patterns=("*.py",),
+    exclude=(),
+    is_running_from_diff=False,
+):
+    return set(
+        expand_paths(
+            paths=paths,
+            stdin_display_name=stdin_display_name,
+            filename_patterns=filename_patterns,
+            exclude=exclude,
+            is_running_from_diff=is_running_from_diff,
+        )
+    )
+
+
+@pytest.mark.usefixtures("files_dir")
+def test_expand_paths_honors_exclude():
+    expected = _normpaths(("./a/b/c.py", "./a/b/e/f.py"))
+    assert _expand_paths(exclude=["d.py"]) == expected
+
+
+@pytest.mark.usefixtures("files_dir")
+def test_expand_paths_defaults_to_dot():
+    expected = _normpaths(("./a/b/c.py", "./a/b/d.py", "./a/b/e/f.py"))
+    assert _expand_paths(paths=()) == expected
+
+
+def test_default_stdin_name_is_not_filtered():
+    assert _expand_paths(paths=("-",)) == {"-"}
+
+
+def test_alternate_stdin_name_is_filtered():
+    ret = _expand_paths(
+        paths=("-",),
+        stdin_display_name="wat",
+        exclude=("wat",),
+    )
+    assert ret == set()
+
+
+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_diff_filenames_filtered_by_patterns(tmp_path):
+    f1 = str(tmp_path.joinpath("f1"))
+    f2 = str(tmp_path.joinpath("f2.py"))
+
+    ret = _expand_paths(paths=(f1, f2), is_running_from_diff=True)
+    assert ret == {f2}
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index 947b67f..eb76572 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -160,6 +160,13 @@ def test_normalize_paths(value, expected):
     assert utils.normalize_paths(value) == expected
 
 
+def test_matches_filename_for_excluding_dotfiles():
+    """Verify that `.` and `..` are not matched by `.*`."""
+    logger = logging.Logger(__name__)
+    assert not utils.matches_filename(".", (".*",), "", logger)
+    assert not utils.matches_filename("..", (".*",), "", logger)
+
+
 @pytest.mark.parametrize(
     "filename,patterns,expected",
     [
@@ -174,89 +181,6 @@ def test_fnmatch(filename, patterns, expected):
     assert utils.fnmatch(filename, patterns) is expected
 
 
-@pytest.fixture
-def files_dir(tmpdir):
-    """Create test dir for testing filenames_from."""
-    with tmpdir.as_cwd():
-        tmpdir.join("a/b/c.py").ensure()
-        tmpdir.join("a/b/d.py").ensure()
-        tmpdir.join("a/b/e/f.py").ensure()
-        yield tmpdir
-
-
-def _normpath(s):
-    return s.replace("/", os.sep)
-
-
-def _normpaths(pths):
-    return {_normpath(pth) for pth in pths}
-
-
-@pytest.mark.usefixtures("files_dir")
-def test_filenames_from_a_directory():
-    """Verify that filenames_from walks a directory."""
-    filenames = set(utils.filenames_from(_normpath("a/b/")))
-    # should include all files
-    expected = _normpaths(("a/b/c.py", "a/b/d.py", "a/b/e/f.py"))
-    assert filenames == expected
-
-
-@pytest.mark.usefixtures("files_dir")
-def test_filenames_from_a_directory_with_a_predicate():
-    """Verify that predicates filter filenames_from."""
-    filenames = set(
-        utils.filenames_from(
-            arg=_normpath("a/b/"),
-            predicate=lambda path: path.endswith(_normpath("b/c.py")),
-        )
-    )
-    # should not include c.py
-    expected = _normpaths(("a/b/d.py", "a/b/e/f.py"))
-    assert filenames == expected
-
-
-@pytest.mark.usefixtures("files_dir")
-def test_filenames_from_a_directory_with_a_predicate_from_the_current_dir():
-    """Verify that predicates filter filenames_from."""
-    filenames = set(
-        utils.filenames_from(
-            arg=_normpath("./a/b"),
-            predicate=lambda path: path == "c.py",
-        )
-    )
-    # none should have matched the predicate so all returned
-    expected = _normpaths(("./a/b/c.py", "./a/b/d.py", "./a/b/e/f.py"))
-    assert filenames == expected
-
-
-@pytest.mark.usefixtures("files_dir")
-def test_filenames_from_a_single_file():
-    """Verify that we simply yield that filename."""
-    filenames = set(utils.filenames_from(_normpath("a/b/c.py")))
-    assert filenames == {_normpath("a/b/c.py")}
-
-
-def test_filenames_from_a_single_file_does_not_exist():
-    """Verify that a passed filename which does not exist is returned back."""
-    filenames = set(utils.filenames_from(_normpath("d/n/e.py")))
-    assert filenames == {_normpath("d/n/e.py")}
-
-
-def test_filenames_from_exclude_doesnt_exclude_directory_names(tmpdir):
-    """Verify that we don't greedily exclude subdirs."""
-    tmpdir.join("1").ensure_dir().join("dont_return_me.py").ensure()
-    tmpdir.join("2").join("1").ensure_dir().join("return_me.py").ensure()
-    exclude = [tmpdir.join("1").strpath]
-
-    # This acts similar to src.flake8.checker.is_path_excluded
-    def predicate(pth):
-        return utils.fnmatch(os.path.abspath(pth), exclude)
-
-    with tmpdir.as_cwd():
-        filenames = list(utils.filenames_from(".", predicate))
-    assert filenames == [os.path.join(".", "2", "1", "return_me.py")]
-
-
 def test_parameters_for_class_plugin():
     """Verify that we can retrieve the parameters for a class plugin."""
 
@@ -323,13 +247,6 @@ def test_parse_unified_diff(diff, parsed_diff):
     assert utils.parse_unified_diff(diff) == parsed_diff
 
 
-def test_matches_filename_for_excluding_dotfiles():
-    """Verify that `.` and `..` are not matched by `.*`."""
-    logger = logging.Logger(__name__)
-    assert not utils.matches_filename(".", (".*",), "", logger)
-    assert not utils.matches_filename("..", (".*",), "", logger)
-
-
 def test_stdin_get_value_crlf():
     """Ensure that stdin is normalized from crlf to lf."""
     stdin = io.TextIOWrapper(io.BytesIO(b"1\r\n2\r\n"), "UTF-8")
diff --git a/tox.ini b/tox.ini
index 4f355d8..6b864e2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -122,4 +122,5 @@ commands =
 extend-ignore = E203
 per-file-ignores =
     src/flake8/formatting/_windows_color.py: N806
+    tests/*: D
 max-complexity = 10