From 0fd28c286698f45b8e42dff737af4787107f97b8 Mon Sep 17 00:00:00 2001
From: Andrew Nesbitt <andrewnez@gmail.com>
Date: Fri, 3 Apr 2026 08:33:55 +0100
Subject: [PATCH] Skip filesystem pattern loading when root is empty

New("") previously resolved "" as CWD and loaded .gitignore,
.git/info/exclude, and global excludes, silently contaminating
matchers intended for programmatic-only use.

Fixes #7
---
 README.md         |  9 ++++++++-
 gitignore.go      |  8 +++++++-
 gitignore_test.go | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 8143997..2fb8bab 100644
--- a/README.md
+++ b/README.md
@@ -33,7 +33,14 @@ For repos with nested `.gitignore` files, `NewFromDirectory` walks the tree and
 m := gitignore.NewFromDirectory("/path/to/repo")
 ```
 
-You can also add patterns manually:
+To create a matcher with only programmatic patterns (no filesystem loading), pass an empty root:
+
+```go
+m := gitignore.New("")
+m.AddPatterns([]byte("*.tmp\n"), "")
+```
+
+You can also add patterns to any matcher manually:
 
 ```go
 m.AddFromFile("/path/to/repo/src/.gitignore", "src")
diff --git a/gitignore.go b/gitignore.go
index 92dcf3d..1900aea 100644
--- a/gitignore.go
+++ b/gitignore.go
@@ -89,10 +89,16 @@ func (m *Matcher) Errors() []PatternError {
 // patterns override earlier ones.
 //
 // The root parameter should be the repository working directory
-// (containing .git/).
+// (containing .git/). If root is empty, no filesystem patterns are
+// loaded and the returned Matcher is empty. Use AddPatterns or
+// AddFromFile to add patterns programmatically.
 func New(root string) *Matcher {
 	m := &Matcher{}
 
+	if root == "" {
+		return m
+	}
+
 	// Read global excludes (lowest priority)
 	if gef := globalExcludesFile(); gef != "" {
 		if data, err := os.ReadFile(gef); err == nil {
diff --git a/gitignore_test.go b/gitignore_test.go
index 89ef219..446a540 100644
--- a/gitignore_test.go
+++ b/gitignore_test.go
@@ -2490,3 +2490,36 @@ func TestAddPatterns(t *testing.T) {
 		}
 	}
 }
+
+func TestNewEmptyRootSkipsFilesystem(t *testing.T) {
+	// Create a temporary directory with a .gitignore that excludes *.exe
+	dir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(dir, ".gitignore"), []byte("*.exe\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Change to that directory so CWD has a .gitignore
+	orig, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Chdir(dir); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := os.Chdir(orig); err != nil {
+			t.Logf("failed to restore working directory: %v", err)
+		}
+	})
+
+	// New("") should not load any filesystem patterns
+	m := gitignore.New("")
+	m.AddPatterns([]byte("*.tmp"), "")
+
+	if m.MatchPath("test.exe", false) {
+		t.Error("New(\"\") should not load .gitignore from CWD, but *.exe matched")
+	}
+	if !m.MatchPath("test.tmp", false) {
+		t.Error("AddPatterns(*.tmp) should still work after New(\"\")")
+	}
+}