fs: Make HasPathPrefix work with relative paths

internal/fs/path_prefix.go

@@ -5,14 +5,15 @@ import (
 )
 
 // HasPathPrefix returns true if p is a subdir of (or a file within) base. It
-// assumes a file system which is case sensitive. For relative paths, false is
-// returned.
+// assumes a file system which is case sensitive. If the paths are not of the
+// same type (one is relative, the other is absolute), false is returned.
 func HasPathPrefix(base, p string) bool {
 	if filepath.VolumeName(base) != filepath.VolumeName(p) {
 		return false
 	}
 
-	if !filepath.IsAbs(base) || !filepath.IsAbs(p) {
+	// handle case when base and p are not of the same type
+	if filepath.IsAbs(base) != filepath.IsAbs(p) {
 		return false
 	}
 

internal/fs/path_prefix_test.go

@@ -21,7 +21,10 @@ func TestHasPathPrefix(t *testing.T) {
 		base, p string
 		result  bool
 	}{
-		{"", "", false},
+		{"", "", true},
+		{".", ".", true},
+		{".", "foo", true},
+		{"foo", ".", false},
 		{"/", "", false},
 		{"/", "x", false},
 		{"x", "/", false},
@@ -36,6 +39,10 @@ func TestHasPathPrefix(t *testing.T) {
 		{"/home/user/foo", "/home/user/foobar", false},
 		{"/home/user/Foo", "/home/user/foo/bar/baz", false},
 		{"/home/user/foo", "/home/user/Foo/bar/baz", false},
+		{"user/foo", "user/foo/bar/baz", true},
+		{"user/foo", "./user/foo", true},
+		{"user/foo", "./user/foo/", true},
+		{"/home/user/foo", "./user/foo/", false},
 	}
 
 	for _, test := range tests {