From bed51280aacb3774ae83933eaff5de8d6cff04dc Mon Sep 17 00:00:00 2001
From: Varun Gandhi <git@cutcul.us>
Date: Mon, 27 Apr 2026 21:57:01 +0200
Subject: [PATCH 1/2] Add failing test for incorrect prefix-based match

--- FAIL: TestMatchAbsoluteRejectsPathWithBasePrefixOnly (0.00s)
    match_test.go:293: unexpected match for path outside base directory; expected nil, got file.txt
FAIL
FAIL    github.com/boyter/gocodewalker/go-gitignore     0.287s
FAIL
---
 go-gitignore/match_test.go | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/go-gitignore/match_test.go b/go-gitignore/match_test.go
index 3ae24e0..2289c60 100644
--- a/go-gitignore/match_test.go
+++ b/go-gitignore/match_test.go
@@ -276,6 +276,24 @@ func TestMatchAbsolute(t *testing.T) {
 	}
 } // TestMatchAbsolute()
 
+func TestMatchAbsoluteRejectsPathWithBasePrefixOnly(t *testing.T) {
+	_buffer, _err := buffer("file.txt\n")
+	if _err != nil {
+		t.Fatalf("unable to create temporary .gitignore: %s", _err.Error())
+	}
+
+	_ignore := gitignore.New(_buffer, _GITBASE, nil)
+	if _ignore == nil {
+		t.Fatal("expected non-nil GitIgnore instance; nil found")
+	}
+
+	_path := _GITBASE + "xfile.txt"
+	_match := _ignore.Absolute(_path, false)
+	if _match != nil {
+		t.Fatalf("unexpected match for path outside base directory; expected nil, got %v", _match)
+	}
+}
+
 func TestMatchRelative(t *testing.T) {
 	// create a temporary .gitignore
 	_buffer, _err := buffer(_GITMATCH)

From 3cd08b4b4649a42c10d32267efe53298c5c3452f Mon Sep 17 00:00:00 2001
From: Varun Gandhi <git@cutcul.us>
Date: Mon, 27 Apr 2026 22:09:40 +0200
Subject: [PATCH 2/2] Fix bug with incorrect handling of prefixes

---
 go-gitignore/gitignore.go  | 20 +++++++++++++-------
 go-gitignore/repository.go |  9 ++-------
 2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/go-gitignore/gitignore.go b/go-gitignore/gitignore.go
index e0b5df2..cce429b 100644
--- a/go-gitignore/gitignore.go
+++ b/go-gitignore/gitignore.go
@@ -268,18 +268,24 @@ func (i *ignore) MatchIsDir(path string, _isdir bool) Match {
 // the path is not located under the base directory of this GitIgnore, or
 // is not matched by this GitIgnore, nil is returned.
 func (i *ignore) Absolute(path string, isdir bool) Match {
-	// does the file share the same directory as this ignore file?
-	if !strings.HasPrefix(path, i._base) {
+	_rel, ok := relativeToBase(i._base, path)
+	if !ok {
 		return nil
 	}
-
-	// extract the relative path of this file
-	_prefix := len(i._base) + 1 // BOYTERWASHERE
-	//_prefix := len(i._base)
-	_rel := string(path[_prefix:])
 	return i.Relative(_rel, isdir)
 } // Absolute()
 
+func relativeToBase(base, path string) (string, bool) {
+	_rel, _err := filepath.Rel(base, path)
+	if _err != nil {
+		return "", false
+	}
+	if _rel == ".." || strings.HasPrefix(_rel, ".."+string(filepath.Separator)) {
+		return "", false
+	}
+	return _rel, true
+}
+
 // Relative attempts to match a path relative to the GitIgnore base
 // directory. isdir is used to indicate whether the path represents a file
 // or a directory. If the path is not matched by the GitIgnore, nil is
diff --git a/go-gitignore/repository.go b/go-gitignore/repository.go
index 1a69cdf..df56f74 100644
--- a/go-gitignore/repository.go
+++ b/go-gitignore/repository.go
@@ -5,7 +5,6 @@ package gitignore
 import (
 	"os"
 	"path/filepath"
-	"strings"
 )
 
 const File = ".gitignore"
@@ -197,14 +196,10 @@ func (r *repository) Match(path string) Match {
 // path is not located under the base directory of this repository, or is not
 // matched by this repository, nil is returned.
 func (r *repository) Absolute(path string, isdir bool) Match {
-	// does the file share the same directory as this ignore file?
-	if !strings.HasPrefix(path, r.Base()) {
+	_rel, ok := relativeToBase(r.Base(), path)
+	if !ok {
 		return nil
 	}
-
-	// extract the relative path of this file
-	_prefix := len(r.Base()) + 1
-	_rel := string(path[_prefix:])
 	return r.Relative(_rel, isdir)
 } // Absolute()