Apply .gitignore correctly in every source entry (#3336)

When passing multiple src directories, the root gitignore was only
applied to the first processed source. The reason is that, in the
first source, exclude is `None`, but then the value gets overridden by
`re_compile_maybe_verbose(DEFAULT_EXCLUDES)`, so in the next iteration
where the source is a directory, the condition is not met and sets the
value of `gitignore` to `None`.

To fix this problem, we store a boolean indicating if `exclude` is
`None` and set the value of `exclude` to its default value if that's
the case. This makes sure that the flow enters the correct condition on
following iterations and also keeps the original value if the condition
is not met.

Also, the value of `gitignore` is initialized as `None` and overriden
if necessary. The value of `root_gitignore` is always calculated to
avoid using additional variables (at the small cost of additional
computations).

Signed-off-by: Antonio Ossa Guerra <aaossa@uc.cl>

CHANGES.md

@@ -22,6 +22,9 @@
 
 <!-- Changes to how Black can be configured -->
 
+- Fix incorrectly ignoring .gitignore presence when more than one source directory is
+  specified (#3336)
+
 ### Packaging
 
 <!-- Changes to how Black is packaged, such as dependency requirements -->

src/black/__init__.py

@@ -30,6 +30,7 @@
 import click
 from click.core import ParameterSource
 from mypy_extensions import mypyc_attr
+from pathspec import PathSpec
 from pathspec.patterns.gitwildmatch import GitWildMatchPatternError
 
 from _black_version import version as __version__
@@ -627,6 +628,11 @@ def get_sources(
     sources: Set[Path] = set()
     root = ctx.obj["root"]
 
+    exclude_is_None = exclude is None
+    exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES) if exclude is None else exclude
+    gitignore = None  # type: Optional[PathSpec]
+    root_gitignore = get_gitignore(root)
+
     for s in src:
         if s == "-" and stdin_filename:
             p = Path(stdin_filename)
@@ -660,16 +666,14 @@ def get_sources(
 
             sources.add(p)
         elif p.is_dir():
-            if exclude is None:
-                exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES)
-                gitignore = get_gitignore(root)
+            if exclude_is_None:
                 p_gitignore = get_gitignore(p)
                 # No need to use p's gitignore if it is identical to root's gitignore
                 # (i.e. root and p point to the same directory).
-                if gitignore != p_gitignore:
-                    gitignore += p_gitignore
-            else:
-                gitignore = None
+                if root_gitignore == p_gitignore:
+                    gitignore = root_gitignore
+                else:
+                    gitignore = root_gitignore + p_gitignore
             sources.update(
                 gen_python_files(
                     p.iterdir(),

tests/data/gitignore_used_on_multiple_sources/.gitignore

@@ -0,0 +1 @@
+a.py

tests/test_black.py

@@ -1998,6 +1998,17 @@ def test_gitignore_used_as_default(self) -> None:
         ctx.obj["root"] = base
         assert_collected_sources(src, expected, ctx=ctx, extend_exclude=r"/exclude/")
 
+    def test_gitignore_used_on_multiple_sources(self) -> None:
+        root = Path(DATA_DIR / "gitignore_used_on_multiple_sources")
+        expected = [
+            root / "dir1" / "b.py",
+            root / "dir2" / "b.py",
+        ]
+        ctx = FakeContext()
+        ctx.obj["root"] = root
+        src = [root / "dir1", root / "dir2"]
+        assert_collected_sources(src, expected, ctx=ctx)
+
     @patch("black.find_project_root", lambda *args: (THIS_DIR.resolve(), None))
     def test_exclude_for_issue_1572(self) -> None:
         # Exclude shouldn't touch files that were explicitly given to Black through the