Reduce matching allocations and skip unrelated ignore rules (#30)

* Reduce matching allocations and skip unrelated ignore rules

* Simplify traversal state and share bracket syntax helpers

* Move refactor tests into gitignore_test.go and note WalkTree subprocess cost

Author: andrew

README.md

@@ -11,7 +11,7 @@ A Go library for matching paths against gitignore rules. Pattern matching uses a
 - Directory-only patterns (trailing `/`) with descendant matching
 - Match provenance via `MatchDetail` (which pattern, file, and line number matched)
 - Invalid pattern surfacing via `Errors()`
-- Literal suffix fast-reject for common patterns like `*.log`
+- Fast rejection for literal names and suffix patterns like `*.log`
 
 ```go
 import "github.com/git-pkgs/gitignore"
@@ -111,7 +111,17 @@ A Matcher is safe for concurrent `Match`/`MatchPath`/`MatchDetail` calls once co
 
 ## Match semantics
 
-Paths should use forward slashes and be relative to the repository root. Last-match-wins, same as git.
+Paths should use forward slashes and be relative to the repository root. An ignored parent directory excludes all its descendants; otherwise, the last matching rule for the path wins.
+
+## Benchmarks
+
+Run benchmarks on an otherwise idle machine, using the same Go toolchain for both revisions. Record repeated samples and memory allocations:
+
+```sh
+go test -run '^$' -bench . -benchmem -count=10 -cpu=1
+```
+
+`BenchmarkCompile` and `BenchmarkWalkTree` include filesystem reads and a Git subprocess through `New`; `BenchmarkAddPatterns` measures parsing without filesystem access. Compare samples with `benchstat` and check the timing spread before quoting speed changes.
 
 ## License
 

conformance_test.go

@@ -148,6 +148,50 @@ func TestConformanceGitStartupFailure(t *testing.T) {
 	}
 }
 
+func TestConformanceNestedWalk(t *testing.T) {
+	requireGit(t)
+	isolateGitEnv(t)
+	paths := parsePathList("a/cache/x\na/keep.log\na/drop.log\na/sub/keep.log\na/sub/drop.log\nb/drop.log\nb/keep.log\nb/cache/x\nblocked/sub/file\n")
+	root := buildRepo(t, "*.log\nblocked/\n", paths)
+	for dir, patterns := range map[string]string{
+		"a": "!keep.log\ncache/\n", "a/sub": "!drop.log\n",
+		"b": "!drop.log\n", "blocked/sub": "!file\n",
+	} {
+		if err := os.WriteFile(filepath.Join(root, dir, ".gitignore"), []byte(patterns), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	want := gitCheckIgnore(t, root, paths)
+	m := gitignore.NewFromDirectory(root)
+	for _, p := range paths {
+		if got := m.Match(p.query()); got != want[p.rel] {
+			t.Errorf("NewFromDirectory Match(%q) = %v, git = %v", p.rel, got, want[p.rel])
+		}
+	}
+	for _, start := range []string{"", "a", "a/sub", "b", "blocked/sub"} {
+		visited := make(map[string]bool)
+		visit := func(path string, _ os.DirEntry) error {
+			visited[filepath.ToSlash(path)] = true
+			return nil
+		}
+		var err error
+		if start == "" {
+			err = gitignore.Walk(root, visit)
+		} else {
+			err = gitignore.WalkFrom(root, start, visit)
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, p := range paths {
+			inScope := start == "" || strings.HasPrefix(p.rel, start+"/")
+			if expected := inScope && !want[p.rel]; visited[p.rel] != expected {
+				t.Errorf("walk from %q: visited %q = %v, want %v", start, p.rel, visited[p.rel], expected)
+			}
+		}
+	}
+}
+
 // TestConformanceFuzz generates random pattern sets and paths, then compares
 // the library against git check-ignore. It is skipped under -short.
 func TestConformanceFuzz(t *testing.T) {