Repository: psf/black

Issue:
File excluded even if explicitly passed via the command line when specified via --exclude 
**Describe the bug**

`--exclude` is supposed to only apply to the recursive discovery of files. Not files explicitly passed to Black through the command line. This is a regression since #1032 was merged.

**To Reproduce** 

1. Create a directory for testing
2. Create and activate a virtual enviroment
3. Install Black on master using `pip install git+git://github.com/psf/black`
4. Create two empty files:
4.1. `pyproject.toml` so Black doesn't find a different configuration file up your directory structure
4.2. `test.py` - this will be our test file
5. Run `black -v --exclude=test.py test.py`
6. Install Black 19.10b0 using `pip install black==19.10b0`
7. Run `black -v --exclude=test.py test.py`
8. Observe that on master the file was excluded and on stable the file was formatted.

**Expected behavior**

Black formats `test.py` since it was explicitly passed through the command line and `--exclude` should not touch such files like it.  

**Environment**

- Version: master (b59a5246577346e6da2cc2802015f08524abf545) and stable (`19.10b0`)
- OS and Python version: `Ubuntu 18.04.04 LTS` and `Python 3.8.1`

**Does this bug also happen on master?**

*Yes and also N/A - This is a regression*

**Additional context**

I haven't looked into this bug that much, but the problem seems to be related to how even files passed via the command line are given to the recursive `gen_python_files` function as single Path object lists in `get_sources`.
https://github.com/psf/black/blob/b59a5246577346e6da2cc2802015f08524abf545/src/black/__init__.py#L605-L610


Discussion:

Resolving patch:
diff --git a/src/black/__init__.py b/src/black/__init__.py
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -583,9 +583,7 @@ def get_sources(
     root = find_project_root(src)
     sources: Set[Path] = set()
     path_empty(src, "No Path provided. Nothing to do 😴", quiet, verbose, ctx)
-    exclude_regexes = [exclude_regex]
-    if force_exclude_regex is not None:
-        exclude_regexes.append(force_exclude_regex)
+    gitignore = get_gitignore(root)
 
     for s in src:
         p = Path(s)
@@ -595,19 +593,30 @@ def get_sources(
                     p.iterdir(),
                     root,
                     include_regex,
-                    exclude_regexes,
+                    exclude_regex,
+                    force_exclude_regex,
                     report,
-                    get_gitignore(root),
+                    gitignore,
                 )
             )
         elif s == "-":
             sources.add(p)
         elif p.is_file():
-            sources.update(
-                gen_python_files(
-                    [p], root, None, exclude_regexes, report, get_gitignore(root)
-                )
-            )
+            normalized_path = normalize_path_maybe_ignore(p, root, report)
+            if normalized_path is None:
+                continue
+
+            normalized_path = "/" + normalized_path
+            # Hard-exclude any files that matches the `--force-exclude` regex.
+            if force_exclude_regex:
+                force_exclude_match = force_exclude_regex.search(normalized_path)
+            else:
+                force_exclude_match = None
+            if force_exclude_match and force_exclude_match.group(0):
+                report.path_ignored(p, "matches the --force-exclude regular expression")
+                continue
+
+            sources.add(p)
         else:
             err(f"invalid path: {s}")
     return sources
@@ -5759,16 +5768,40 @@ def get_gitignore(root: Path) -> PathSpec:
     return PathSpec.from_lines("gitwildmatch", lines)
 
 
+def normalize_path_maybe_ignore(
+    path: Path, root: Path, report: "Report"
+) -> Optional[str]:
+    """Normalize `path`. May return `None` if `path` was ignored.
+
+    `report` is where "path ignored" output goes.
+    """
+    try:
+        normalized_path = path.resolve().relative_to(root).as_posix()
+    except OSError as e:
+        report.path_ignored(path, f"cannot be read because {e}")
+        return None
+
+    except ValueError:
+        if path.is_symlink():
+            report.path_ignored(path, f"is a symbolic link that points outside {root}")
+            return None
+
+        raise
+
+    return normalized_path
+
+
 def gen_python_files(
     paths: Iterable[Path],
     root: Path,
     include: Optional[Pattern[str]],
-    exclude_regexes: Iterable[Pattern[str]],
+    exclude: Pattern[str],
+    force_exclude: Optional[Pattern[str]],
     report: "Report",
     gitignore: PathSpec,
 ) -> Iterator[Path]:
     """Generate all files under `path` whose paths are not excluded by the
-    `exclude` regex, but are included by the `include` regex.
+    `exclude_regex` or `force_exclude` regexes, but are included by the `include` regex.
 
     Symbolic links pointing outside of the `root` directory are ignored.
 
@@ -5776,43 +5809,41 @@ def gen_python_files(
     """
     assert root.is_absolute(), f"INTERNAL ERROR: `root` must be absolute but is {root}"
     for child in paths:
-        # Then ignore with `exclude` option.
-        try:
-            normalized_path = child.resolve().relative_to(root).as_posix()
-        except OSError as e:
-            report.path_ignored(child, f"cannot be read because {e}")
+        normalized_path = normalize_path_maybe_ignore(child, root, report)
+        if normalized_path is None:
             continue
-        except ValueError:
-            if child.is_symlink():
-                report.path_ignored(
-                    child, f"is a symbolic link that points outside {root}"
-                )
-                continue
-
-            raise
 
         # First ignore files matching .gitignore
         if gitignore.match_file(normalized_path):
             report.path_ignored(child, "matches the .gitignore file content")
             continue
 
+        # Then ignore with `--exclude` and `--force-exclude` options.
         normalized_path = "/" + normalized_path
         if child.is_dir():
             normalized_path += "/"
 
-        is_excluded = False
-        for exclude in exclude_regexes:
-            exclude_match = exclude.search(normalized_path) if exclude else None
-            if exclude_match and exclude_match.group(0):
-                report.path_ignored(child, "matches the --exclude regular expression")
-                is_excluded = True
-                break
-        if is_excluded:
+        exclude_match = exclude.search(normalized_path) if exclude else None
+        if exclude_match and exclude_match.group(0):
+            report.path_ignored(child, "matches the --exclude regular expression")
+            continue
+
+        force_exclude_match = (
+            force_exclude.search(normalized_path) if force_exclude else None
+        )
+        if force_exclude_match and force_exclude_match.group(0):
+            report.path_ignored(child, "matches the --force-exclude regular expression")
             continue
 
         if child.is_dir():
             yield from gen_python_files(
-                child.iterdir(), root, include, exclude_regexes, report, gitignore
+                child.iterdir(),
+                root,
+                include,
+                exclude,
+                force_exclude,
+                report,
+                gitignore,
             )
 
         elif child.is_file():


Test patch:
diff --git a/tests/test_black.py b/tests/test_black.py
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -110,6 +110,20 @@ def skip_if_exception(e: str) -> Iterator[None]:
             raise
 
 
+class FakeContext(click.Context):
+    """A fake click Context for when calling functions that need it."""
+
+    def __init__(self) -> None:
+        self.default_map: Dict[str, Any] = {}
+
+
+class FakeParameter(click.Parameter):
+    """A fake click Parameter for when calling functions that need it."""
+
+    def __init__(self) -> None:
+        pass
+
+
 class BlackRunner(CliRunner):
     """Modify CliRunner so that stderr is not merged with stdout.
 
@@ -1551,7 +1565,32 @@ def test_include_exclude(self) -> None:
         this_abs = THIS_DIR.resolve()
         sources.extend(
             black.gen_python_files(
-                path.iterdir(), this_abs, include, [exclude], report, gitignore
+                path.iterdir(), this_abs, include, exclude, None, report, gitignore
+            )
+        )
+        self.assertEqual(sorted(expected), sorted(sources))
+
+    @patch("black.find_project_root", lambda *args: THIS_DIR.resolve())
+    def test_exclude_for_issue_1572(self) -> None:
+        # Exclude shouldn't touch files that were explicitly given to Black through the
+        # CLI. Exclude is supposed to only apply to the recursive discovery of files.
+        # https://github.com/psf/black/issues/1572
+        path = THIS_DIR / "data" / "include_exclude_tests"
+        include = ""
+        exclude = r"/exclude/|a\.py"
+        src = str(path / "b/exclude/a.py")
+        report = black.Report()
+        expected = [Path(path / "b/exclude/a.py")]
+        sources = list(
+            black.get_sources(
+                ctx=FakeContext(),
+                src=(src,),
+                quiet=True,
+                verbose=False,
+                include=include,
+                exclude=exclude,
+                force_exclude=None,
+                report=report,
             )
         )
         self.assertEqual(sorted(expected), sorted(sources))
@@ -1572,7 +1611,7 @@ def test_gitignore_exclude(self) -> None:
         this_abs = THIS_DIR.resolve()
         sources.extend(
             black.gen_python_files(
-                path.iterdir(), this_abs, include, [exclude], report, gitignore
+                path.iterdir(), this_abs, include, exclude, None, report, gitignore
             )
         )
         self.assertEqual(sorted(expected), sorted(sources))
@@ -1600,7 +1639,8 @@ def test_empty_include(self) -> None:
                 path.iterdir(),
                 this_abs,
                 empty,
-                [re.compile(black.DEFAULT_EXCLUDES)],
+                re.compile(black.DEFAULT_EXCLUDES),
+                None,
                 report,
                 gitignore,
             )
@@ -1627,7 +1667,8 @@ def test_empty_exclude(self) -> None:
                 path.iterdir(),
                 this_abs,
                 re.compile(black.DEFAULT_INCLUDES),
-                [empty],
+                empty,
+                None,
                 report,
                 gitignore,
             )
@@ -1684,7 +1725,7 @@ def test_symlink_out_of_root_directory(self) -> None:
         try:
             list(
                 black.gen_python_files(
-                    path.iterdir(), root, include, exclude, report, gitignore
+                    path.iterdir(), root, include, exclude, None, report, gitignore
                 )
             )
         except ValueError as ve:
@@ -1698,7 +1739,7 @@ def test_symlink_out_of_root_directory(self) -> None:
         with self.assertRaises(ValueError):
             list(
                 black.gen_python_files(
-                    path.iterdir(), root, include, exclude, report, gitignore
+                    path.iterdir(), root, include, exclude, None, report, gitignore
                 )
             )
         path.iterdir.assert_called()
@@ -1777,16 +1818,6 @@ def test_parse_pyproject_toml(self) -> None:
 
     def test_read_pyproject_toml(self) -> None:
         test_toml_file = THIS_DIR / "test.toml"
-
-        # Fake a click context and parameter so mypy stays happy
-        class FakeContext(click.Context):
-            def __init__(self) -> None:
-                self.default_map: Dict[str, Any] = {}
-
-        class FakeParameter(click.Parameter):
-            def __init__(self) -> None:
-                pass
-
         fake_ctx = FakeContext()
         black.read_pyproject_toml(
             fake_ctx, FakeParameter(), str(test_toml_file),