fix: handle errors reading go licenses (#2985)

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

syft/pkg/cataloger/golang/licenses.go

@@ -138,7 +138,15 @@ func (c *goLicenseResolver) getLicensesFromRemote(moduleName, moduleVersion stri
 
 func (c *goLicenseResolver) findLicensesInFS(urlPrefix string, fsys fs.FS) ([]goLicense, error) {
 	var out []goLicense
-	err := fs.WalkDir(fsys, ".", func(filePath string, d fs.DirEntry, _ error) error {
+	err := fs.WalkDir(fsys, ".", func(filePath string, d fs.DirEntry, err error) error {
+		if err != nil {
+			log.Debugf("error reading %s#%s: %v", urlPrefix, filePath, err)
+			return err
+		}
+		if d == nil {
+			log.Debugf("nil entry for %s#%s", urlPrefix, filePath)
+			return nil
+		}
 		if !c.lowerLicenseFileNames.Has(strings.ToLower(d.Name())) {
 			return nil
 		}

syft/pkg/cataloger/golang/licenses_test.go

@@ -4,6 +4,7 @@ import (
 	"archive/zip"
 	"bytes"
 	"fmt"
+	"io/fs"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -244,3 +245,62 @@ func Test_findVersionPath(t *testing.T) {
 	vp := findVersionPath(f, ".")
 	require.Equal(t, "github.com/someorg/somepkg@version", vp)
 }
+
+func Test_walkDirErrors(t *testing.T) {
+	resolver := newGoLicenseResolver("", CatalogerConfig{})
+	_, err := resolver.findLicensesInFS("somewhere", badFS{})
+	require.Error(t, err)
+}
+
+type badFS struct{}
+
+func (b badFS) Open(_ string) (fs.File, error) {
+	return nil, fmt.Errorf("error")
+}
+
+var _ fs.FS = (*badFS)(nil)
+
+func Test_noLocalGoModDir(t *testing.T) {
+	emptyTmp := t.TempDir()
+
+	validTmp := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(validTmp, "mod@ver"), 0700|os.ModeDir))
+
+	tests := []struct {
+		name    string
+		dir     string
+		wantErr require.ErrorAssertionFunc
+	}{
+		{
+			name:    "empty",
+			dir:     "",
+			wantErr: require.Error,
+		},
+		{
+			name:    "invalid dir",
+			dir:     filepath.Join(emptyTmp, "invalid-dir"),
+			wantErr: require.Error,
+		},
+		{
+			name:    "missing mod dir",
+			dir:     emptyTmp,
+			wantErr: require.Error,
+		},
+		{
+			name:    "valid mod dir",
+			dir:     validTmp,
+			wantErr: require.NoError,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			resolver := newGoLicenseResolver("", CatalogerConfig{
+				SearchLocalModCacheLicenses: true,
+				LocalModCacheDir:            test.dir,
+			})
+			_, err := resolver.getLicensesFromLocal("mod", "ver")
+			test.wantErr(t, err)
+		})
+	}
+}