fix(source): treat exclude paths with trailing slash as directories (#4892)

A trailing slash on --exclude (e.g. './lib/') is dropped during pattern
normalization but doublestar.Match still requires an exact string match,
so the resulting pattern silently matches nothing and the directory is
not excluded. Strip a trailing slash so './lib/' and './lib' behave the
same.

Fixes #4839

Signed-off-by: ChrisJr404 <chris@hacknow.com>

syft/source/directorysource/directory_source.go

@@ -145,6 +145,9 @@ func GetDirectoryExclusionFunctions(root string, exclusions []string) ([]fileres
 		// check exclusions for supported paths, these are all relative to the "scan root"
 		if strings.HasPrefix(exclusion, "./") || strings.HasPrefix(exclusion, "*/") || strings.HasPrefix(exclusion, "**/") {
 			exclusion = strings.TrimPrefix(exclusion, "./")
+			// a trailing slash signals a directory but is otherwise discarded by doublestar.Match,
+			// causing the pattern to silently match nothing (see issue #4839)
+			exclusion = strings.TrimSuffix(exclusion, "/")
 			exclusions[idx] = root + exclusion
 		} else {
 			errors = append(errors, exclusion)

syft/source/directorysource/directory_source_test.go

@@ -175,6 +175,18 @@ func Test_DirectorySource_Exclusions(t *testing.T) {
 			},
 			exclusions: []string{"./target"},
 		},
+		{
+			input: "testdata/image-simple",
+			desc:  "exclude explicit directory with trailing slash (issue #4839)",
+			glob:  "**",
+			expected: []string{
+				"Dockerfile",
+				"file-1.txt",
+				"file-2.txt",
+				//"target/really/nested/file-3.txt", // explicitly skipped
+			},
+			exclusions: []string{"./target/"},
+		},
 		{
 			input: "testdata/image-simple",
 			desc:  "exclude explicit file relative to the root",
@@ -329,6 +341,14 @@ func Test_getDirectoryExclusionFunctions_crossPlatform(t *testing.T) {
 			finfo:    file.ManualInfo{ModeValue: os.ModeDir},
 			walkHint: fs.SkipDir,
 		},
+		{
+			desc:     "directory exclusion with trailing slash (issue #4839)",
+			root:     "/usr/var",
+			path:     "/usr/var/lib",
+			exclude:  "./lib/",
+			finfo:    file.ManualInfo{ModeValue: os.ModeDir},
+			walkHint: fs.SkipDir,
+		},
 		{
 			desc:     "no file info",
 			root:     "/",