fix: don't traverse into excluded directories

src/scikit_build_core/build/_file_processor.py

@@ -7,7 +7,8 @@
 
 import pathspec
 
-from scikit_build_core.format import pyproject_format
+from .._logging import logger
+from ..format import pyproject_format
 
 if TYPE_CHECKING:
     from collections.abc import Generator, Sequence
@@ -65,33 +66,93 @@ def each_unignored_file(
 
     include_spec = pathspec.GitIgnoreSpec.from_lines(include)
 
-    for dirstr, _, filenames in os.walk(str(starting_path), followlinks=True):
+    for dirstr, dirs, filenames in os.walk(str(starting_path), followlinks=True):
         dirpath = Path(dirstr)
-        all_paths = (dirpath / fn for fn in filenames)
-        for p in all_paths:
-            # Always include something included
-            if include_spec.match_file(p):
-                yield p
-                continue
-
-            # Always exclude something excluded
-            if user_exclude_spec.match_file(p):
-                continue
-
-            # Ignore from global ignore
-            if global_exclude_spec.match_file(p):
-                continue
-
-            # Ignore built-in patterns
-            if builtin_exclude_spec.match_file(p):
-                continue
-
-            # Check relative ignores (Python 3.9's is_relative_to workaround)
-            if any(
-                nex.match_file(p.relative_to(np))
-                for np, nex in nested_excludes.items()
-                if dirpath == np or np in dirpath.parents
+        for dname in dirs:
+            if not match_path(
+                dirpath,
+                dirpath / dname,
+                include_spec,
+                global_exclude_spec,
+                builtin_exclude_spec,
+                user_exclude_spec,
+                nested_excludes,
+                is_path=True,
             ):
-                continue
+                dirs.remove(dname)
+
+        for fn in filenames:
+            path = dirpath / fn
+            if match_path(
+                dirpath,
+                path,
+                include_spec,
+                global_exclude_spec,
+                builtin_exclude_spec,
+                user_exclude_spec,
+                nested_excludes,
+                is_path=False,
+            ):
+                yield path
+
+
+def match_path(
+    dirpath: Path,
+    p: Path,
+    include_spec: pathspec.GitIgnoreSpec,
+    global_exclude_spec: pathspec.GitIgnoreSpec,
+    builtin_exclude_spec: pathspec.GitIgnoreSpec,
+    user_exclude_spec: pathspec.GitIgnoreSpec,
+    nested_excludes: dict[Path, pathspec.GitIgnoreSpec],
+    *,
+    is_path: bool,
+) -> bool:
+    ptype = "directory" if is_path else "file"
+
+    # Always include something included
+    if include_spec.match_file(p):
+        logger.info("Including {} {} because it is explicitly included.", ptype, p)
+        return True
+
+    # Always exclude something excluded
+    if user_exclude_spec.match_file(p):
+        logger.info(
+            "Excluding {} {} because it is explicitly excluded by the user.", ptype, p
+        )
+        return False
+
+    # Ignore from global ignore
+    if global_exclude_spec.match_file(p):
+        logger.info(
+            "Excluding {} {} because it is explicitly excluded by the global ignore.",
+            ptype,
+            p,
+        )
+        return False
+
+    # Ignore built-in patterns
+    if builtin_exclude_spec.match_file(p):
+        logger.info(
+            "Excluding {} {} because it is explicitly excluded by the built-in ignore.",
+            ptype,
+            p,
+        )
+        return False
+
+    # Check relative ignores (Python 3.9's is_relative_to workaround)
+    if any(
+        nex.match_file(p.relative_to(np))
+        for np, nex in nested_excludes.items()
+        if dirpath == np or np in dirpath.parents
+    ):
+        logger.info(
+            "Excluding {} {} because it is explicitly included by nested ignore.",
+            ptype,
+            p,
+        )
+        return False
 
-            yield p
+    logger.info(
+        "Including {} {} because it exists (and isn't matched any other way).", ptype, p
+    )
+    return True