Load .gitignore and exclude regex at time of use

Loading .gitignore and compiling the exclude regex can take more than
15ms. We shouldn't and don't need to pay this cost if we're simply
formatting files given on the command line directly.

I would've loved to lazily import pathspec, but the patch won't be clean
until the file collection and discovery logic is refactored first.

Co-authored-by: Fabio Zadrozny <fabiofz@gmail.com>

diff --git a/src/black/__init__.py b/src/black/__init__.py
index afc76e1fa0cb5e7dda1a51544718ef778e846344..117dc832c9891c61a6433b5fcdc6a077a4c3dfed 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -623,12 +623,7 @@ def get_sources(
 ) -> Set[Path]:
     """Compute the set of files to be formatted."""
     sources: Set[Path] = set()
-
-    if exclude is None:
-        exclude = re_compile_maybe_verbose(DEFAULT_EXCLUDES)
-        gitignore = get_gitignore(ctx.obj["root"])
-    else:
-        gitignore = None
+    root = ctx.obj["root"]
 
     for s in src:
         if s == "-" and stdin_filename:
@@ -663,6 +658,11 @@ 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)
+            else:
+                gitignore = None
             sources.update(
                 gen_python_files(
                     p.iterdir(),