fix: handle errors reading go licenses (#2985)

Signed-off-by: Keith Zantow <kzantow@gmail.com>

internal/cache/filesystem.go

@@ -87,7 +87,7 @@ func subFs(fsys afero.Fs, subDirs ...string) (afero.Fs, error) {
 	if errors.Is(err, afero.ErrFileNotFound) {
 		err = fsys.MkdirAll(dir, dirPermissions)
 		if err != nil {
-			return nil, fmt.Errorf("unable to create directory at '%s/%s': %v", dir, strings.Join(subDirs, "/"), err)
+			return nil, fmt.Errorf("unable to create directory at '%s': %v", dir, err)
 		}
 		stat, err = fsys.Stat(dir)
 		if err != nil {

internal/cache/filesystem_test.go

@@ -1,6 +1,7 @@
 package cache
 
 import (
+	"fmt"
 	"io"
 	"net/url"
 	"os"
@@ -92,3 +93,14 @@ func Test_makeDiskKey(t *testing.T) {
 		})
 	}
 }
+
+func Test_errors(t *testing.T) {
+	tmp := t.TempDir()
+	cache := filepath.Join(tmp, "cache")
+	// make a non-writable directory
+	require.NoError(t, os.MkdirAll(cache, 0500|os.ModeDir))
+	// attempt to make cache in non-writable directory
+	dir := filepath.Join(cache, "dir")
+	_, err := NewFromDir(dir, time.Hour)
+	require.ErrorContains(t, err, fmt.Sprintf("unable to create directory at '%s':", dir))
+}