Reprocess all rules after a LexerMutator is applied.

mutators.go

@@ -45,7 +45,7 @@ func Include(state string) Rule {
 }
 
 func (i *includeMutator) Mutate(s *LexerState) error {
-	panic(fmt.Errorf("should never reach here Include(%q)", i.state))
+	return fmt.Errorf("should never reach here Include(%q)", i.state)
 }
 
 func (i *includeMutator) MutateLexer(rules CompiledRules, state string, rule int) error {
@@ -67,7 +67,7 @@ func Combined(states ...string) Mutator {
 }
 
 func (c *combinedMutator) Mutate(s *LexerState) error {
-	panic(fmt.Errorf("should never reach here Combined(%v)", c.states))
+	return fmt.Errorf("should never reach here Combined(%v)", c.states)
 }
 
 func (c *combinedMutator) MutateLexer(rules CompiledRules, state string, rule int) error {

regexp.go

@@ -272,15 +272,23 @@ func (r *RegexLexer) maybeCompile() (err error) {
 			}
 		}
 	}
+restart:
+	seen := map[LexerMutator]bool{}
 	for state := range r.rules {
 		for i := 0; i < len(r.rules[state]); i++ {
 			rule := r.rules[state][i]
 			if compile, ok := rule.Mutator.(LexerMutator); ok {
+				if seen[compile] {
+					return fmt.Errorf("saw mutator %T twice; this should not happen", compile)
+				}
+				seen[compile] = true
 				if err := compile.MutateLexer(r.rules, state, i); err != nil {
 					return err
 				}
 				// Process the rules again in case the mutator added/removed rules.
-				i = -1
+				//
+				// This sounds bad, but shouldn't be significant in practice.
+				goto restart
 			}
 		}
 	}