go bindings: Don't panic on half-finished descriptors (#171)

bindings/go/scip/symbol.go

@@ -96,7 +96,10 @@ func (s *symbolParser) error(message string) error {
 }
 
 func (s *symbolParser) current() rune {
-	return s.Symbol[s.index]
+	if s.index < len(s.Symbol) {
+		return s.Symbol[s.index]
+	}
+	return '\x00'
 }
 
 func (s *symbolParser) peekNext() rune {
@@ -119,6 +122,7 @@ func (s *symbolParser) parseDescriptors() ([]*Descriptor, error) {
 }
 
 func (s *symbolParser) parseDescriptor() (*Descriptor, error) {
+	start := s.index
 	switch s.peekNext() {
 	case '(':
 		s.index++
@@ -168,7 +172,12 @@ func (s *symbolParser) parseDescriptor() (*Descriptor, error) {
 		default:
 		}
 	}
-	return nil, nil
+
+	end := s.index
+	if s.index > len(s.Symbol) {
+		end = len(s.Symbol)
+	}
+	return nil, errors.Newf("unrecognized descriptor %q", string(s.Symbol[start:end]))
 }
 
 func (s *symbolParser) acceptIdentifier(what string) (string, error) {

bindings/go/scip/symbol_test.go

@@ -81,3 +81,16 @@ func TestParseSymbol(t *testing.T) {
 		})
 	}
 }
+
+func TestParseSymbolNoCrash(t *testing.T) {
+	for _, symbolName := range []string{
+		"lsif-java maven package 1.0.0",
+		"lsif-java maven package 1.0.0 java/io/File#Entry.trailingstring",
+		"lsif-java maven package 1.0.0 java/io/File#Entry.unrecognizedSuffix@",
+	} {
+
+		if _, err := ParseSymbol(symbolName); err == nil {
+			t.Fatalf("expected error from parsing %q", symbolName)
+		}
+	}
+}