Apply .gitignore files considering their location

When a .gitignore file contains the special rule to ignore every
subfolder content (`*/*`) and the file is located in a subfolder
relative to where the command is executed (root), the rule is
incorrectly applied and ignores every file at the same level of the
.gitignore file.

The reason for this is that the `gitignore` variable accumulates the
rules found in each .gitignore while traversing files and directories
recursively. This makes sense and, in general, works as expected. The
problem is that the gitignore rules are applied using as the root of
the target directory as a reference. This is the cause of the bug.

The implemented solution keeps track of every .gitignore file found
while traversing the targets and the location of each .gitignore.
Then, when matching files to the .gitignore rules, compare each set of
rules with the appropiate relative path to the candidate target file.

To make this possible, we changed the single `gitignore` object with a
dictionary of similar objects, where the corresponding key is the path
to the folder that contains that .gitignore file. This required
changing the signature of the `get_sources` function. Also, we
introduce a `is_ignored` function that compares a file with every set
of rules. Finally, some tests required an update to pass the gitignore
object in the new format.

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

src/black/__init__.py

@@ -625,6 +625,8 @@ def get_sources(
     sources: Set[Path] = set()
     root = ctx.obj["root"]
 
+    gitignore = None
+
     for s in src:
         if s == "-" and stdin_filename:
             p = Path(stdin_filename)
@@ -660,14 +662,14 @@ def get_sources(
         elif p.is_dir():
             if exclude is None:
                 exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES)
-                gitignore = get_gitignore(root)
+                root_gitignore = get_gitignore(root)
                 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: root_gitignore, p: p_gitignore}
+                else:
+                    gitignore = {root: root_gitignore}
             sources.update(
                 gen_python_files(
                     p.iterdir(),

src/black/files.py

@@ -198,7 +198,7 @@ def gen_python_files(
     extend_exclude: Optional[Pattern[str]],
     force_exclude: Optional[Pattern[str]],
     report: Report,
-    gitignore: Optional[PathSpec],
+    gitignore: Optional[Dict[Path, PathSpec]],
     *,
     verbose: bool,
     quiet: bool,
@@ -211,15 +211,25 @@ def gen_python_files(
 
     `report` is where output about exclusions goes.
     """
+
+    def is_ignored(gitignore_dict, child, report):
+        for _dir, _gitignore in gitignore_dict.items():
+            relative_path = normalize_path_maybe_ignore(child, _dir, report)
+            if relative_path is None:
+                continue
+            if _gitignore is not None and _gitignore.match_file(relative_path):
+                report.path_ignored(child, "matches the .gitignore file content")
+                return True
+        return False
+
     assert root.is_absolute(), f"INTERNAL ERROR: `root` must be absolute but is {root}"
     for child in paths:
         normalized_path = normalize_path_maybe_ignore(child, root, report)
         if normalized_path is None:
             continue
 
         # First ignore files matching .gitignore, if passed
-        if gitignore is not None and gitignore.match_file(normalized_path):
-            report.path_ignored(child, "matches the .gitignore file content")
+        if gitignore is not None and is_ignored(gitignore, child, report):
             continue
 
         # Then ignore with `--exclude` `--extend-exclude` and `--force-exclude` options.
@@ -244,6 +254,11 @@ def gen_python_files(
         if child.is_dir():
             # If gitignore is None, gitignore usage is disabled, while a Falsey
             # gitignore is when the directory doesn't have a .gitignore file.
+            if gitignore is None:
+                _gitignore = None
+            else:
+                _gitignore = gitignore.copy()
+                _gitignore[child] = get_gitignore(child)
             yield from gen_python_files(
                 child.iterdir(),
                 root,
@@ -252,7 +267,7 @@ def gen_python_files(
                 extend_exclude,
                 force_exclude,
                 report,
-                gitignore + get_gitignore(child) if gitignore is not None else None,
+                _gitignore,
                 verbose=verbose,
                 quiet=quiet,
             )

tests/test_black.py

@@ -1989,7 +1989,7 @@ def test_gitignore_exclude(self) -> None:
                 None,
                 None,
                 report,
-                gitignore,
+                {path: gitignore},
                 verbose=False,
                 quiet=False,
             )
@@ -2018,7 +2018,7 @@ def test_nested_gitignore(self) -> None:
                 None,
                 None,
                 report,
-                root_gitignore,
+                {path: root_gitignore},
                 verbose=False,
                 quiet=False,
             )
@@ -2110,7 +2110,7 @@ def test_symlink_out_of_root_directory(self) -> None:
                     None,
                     None,
                     report,
-                    gitignore,
+                    {path: gitignore},
                     verbose=False,
                     quiet=False,
                 )