test(hooks): cover compound-selector regression in CSS class prefix hook (#3702)

Adds tests/hooks/test_check_css_class_prefix.py to lock in the fix from
PR #3103. Each compound-selector class (.foo.bar, .a.b.c, .foo.bar:hover)
must be validated; URL hostnames in url(...) and dotted paths must still
be skipped; descendant selectors, allowlisted framework classes, comments,
@import statements, and the same regex inside HTML <style> blocks are all
covered. Reverting the regex to the pre-fix form makes 4 of these tests
fail, confirming they catch the original bug.

tests/hooks/test_check_css_class_prefix.py

@@ -0,0 +1,166 @@
+"""
+Tests for the check-css-class-prefix pre-commit hook.
+
+Specifically guards against the regex regression fixed in PR #3103, where
+`(?<![\\w/])\\.` matched only the first class in a compound selector like
+`.class1.class2` because the leading dot of the second class was preceded
+by a word character. That hid 159+ unprefixed compound state classes such
+as `.ldr-foo.selected` or `.ldr-foo.loading` from the prefix check.
+"""
+
+import subprocess
+import sys
+import tempfile
+from pathlib import Path
+
+import pytest
+
+
+HOOK_SCRIPT = (
+    Path(__file__).parent.parent.parent
+    / ".pre-commit-hooks"
+    / "check-css-class-prefix.py"
+)
+
+
+def _run_hook(content: str, filename: str) -> subprocess.CompletedProcess:
+    """Write content to a temp file and run the hook against it."""
+    with tempfile.TemporaryDirectory() as d:
+        path = Path(d) / filename
+        path.parent.mkdir(parents=True, exist_ok=True)
+        path.write_text(content)
+        return subprocess.run(
+            [sys.executable, str(HOOK_SCRIPT), str(path)],
+            capture_output=True,
+            text=True,
+        )
+
+
+class TestCompoundSelectorsCSS:
+    """The fix in PR #3103: every class in a compound selector must be checked."""
+
+    def test_compound_selector_first_class_unprefixed_is_caught(self):
+        """`.bare.ldr-other` must fail on `.bare`."""
+        result = _run_hook(".bare.ldr-other { color: red; }\n", "x.css")
+        assert result.returncode == 1
+        assert "'.bare'" in result.stdout
+
+    def test_compound_selector_second_class_unprefixed_is_caught(self):
+        """`.ldr-foo.selected` was previously silently passing — must fail now."""
+        result = _run_hook(".ldr-foo.selected { color: red; }\n", "x.css")
+        assert result.returncode == 1
+        assert "'.selected'" in result.stdout
+
+    def test_compound_selector_three_classes_all_validated(self):
+        """`.ldr-a.bare.ldr-c` must fail on the middle bare class."""
+        result = _run_hook(".ldr-a.bare.ldr-c { color: red; }\n", "x.css")
+        assert result.returncode == 1
+        assert "'.bare'" in result.stdout
+
+    def test_compound_selector_all_prefixed_passes(self):
+        """`.ldr-foo.ldr-bar` is valid — all classes have the prefix."""
+        result = _run_hook(".ldr-foo.ldr-bar { color: red; }\n", "x.css")
+        assert result.returncode == 0
+
+    def test_compound_with_pseudo_class_validates_real_classes(self):
+        """`.ldr-foo.bare:hover` must fail on `.bare`, not on `:hover`."""
+        result = _run_hook(".ldr-foo.bare:hover { color: red; }\n", "x.css")
+        assert result.returncode == 1
+        assert "'.bare'" in result.stdout
+        assert "'.hover'" not in result.stdout
+
+
+class TestDescendantSelectorsCSS:
+    """Space-separated selectors must continue to validate each class."""
+
+    def test_descendant_selector_with_unprefixed_child_fails(self):
+        result = _run_hook(".ldr-parent .bare { color: red; }\n", "x.css")
+        assert result.returncode == 1
+        assert "'.bare'" in result.stdout
+
+    def test_descendant_selector_all_prefixed_passes(self):
+        result = _run_hook(".ldr-parent .ldr-child { color: red; }\n", "x.css")
+        assert result.returncode == 0
+
+
+class TestUrlsAreNotMatched:
+    """The hook's lookbehind must continue to skip dots inside URL hostnames."""
+
+    def test_url_in_background_image_is_not_flagged(self):
+        css = (
+            ".ldr-foo {\n"
+            "    background: url(https://www.example.com/spinner.svg);\n"
+            "}\n"
+        )
+        result = _run_hook(css, "x.css")
+        assert result.returncode == 0
+
+    def test_unquoted_url_with_dotted_path_is_not_flagged(self):
+        css = ".ldr-foo { background: url(www.w3.org/path); }\n"
+        result = _run_hook(css, "x.css")
+        assert result.returncode == 0
+
+
+class TestAllowlistedClasses:
+    """Bootstrap and other framework classes must pass the prefix check."""
+
+    @pytest.mark.parametrize(
+        "selector",
+        [
+            ".container",
+            ".form-group",
+            ".btn-primary",
+            ".active",
+            ".disabled",
+            ".visually-hidden",
+            ".bi-search",
+            ".fa-spinner",
+        ],
+    )
+    def test_allowed_framework_class_passes(self, selector: str):
+        result = _run_hook(f"{selector} {{ color: red; }}\n", "x.css")
+        assert result.returncode == 0
+
+    def test_compound_with_allowlisted_modifier_passes(self):
+        """`.ldr-foo.active` must pass — `active` is allowlisted."""
+        result = _run_hook(".ldr-foo.active { color: red; }\n", "x.css")
+        assert result.returncode == 0
+
+
+class TestCommentsAndImportsSkipped:
+    """Lines that are CSS comments or @import should not be scanned."""
+
+    def test_unprefixed_class_inside_comment_is_ignored(self):
+        css = "/* .bare-class is mentioned but not defined here */\n"
+        result = _run_hook(css, "x.css")
+        assert result.returncode == 0
+
+    def test_import_statement_is_skipped(self):
+        css = '@import url("./other.bare-thing.css");\n'
+        result = _run_hook(css, "x.css")
+        assert result.returncode == 0
+
+
+class TestStyleTagInHTML:
+    """The HTML scanner uses the same regex inside <style> blocks."""
+
+    def test_compound_selector_in_style_tag_is_caught(self):
+        html = (
+            "<html><head><style>\n"
+            ".ldr-foo.bare { color: red; }\n"
+            "</style></head></html>\n"
+        )
+        result = _run_hook(html, "x.html")
+        assert result.returncode == 1
+        assert "'.bare'" in result.stdout
+        assert "in style tag" in result.stdout
+
+    def test_compound_selector_outside_style_tag_falls_through_to_attr_check(
+        self,
+    ):
+        """A `.ldr-foo.bare` literal outside <style> isn't a CSS rule definition;
+        the attribute scanner only inspects class="..." attributes, so it
+        shouldn't flag this content as either a CSS or HTML class issue."""
+        html = '<div data-css=".ldr-foo.bare">x</div>\n'
+        result = _run_hook(html, "x.html")
+        assert result.returncode == 0