Detect duplicate names between terminals and non-terminals

3 files changed, 38 insertions, 4 deletions

diff --git a/driver/parser_test.go b/driver/parser_test.go
index 8145d7b..5763d63 100644
--- a/driver/parser_test.go
+++ b/driver/parser_test.go
@@ -369,6 +369,32 @@ bar: "bar";
 `,
 			specErr: true,
 		},
+		// A terminal and a non-terminal (start symbol) are duplicates.
+		{
+			specSrc: `
+a
+    : foo
+    ;
+foo: "foo";
+a: "a";
+`,
+			specErr: true,
+		},
+		// A terminal and a non-terminal (not start symbol) are duplicates.
+		{
+			specSrc: `
+a
+    : foo
+    ;
+b
+    : bar
+    ;
+foo: "foo";
+bar: "bar";
+b: "a";
+`,
+			specErr: true,
+		},
 	}
 	for i, tt := range tests {
 		t.Run(fmt.Sprintf("#%v", i), func(t *testing.T) {
diff --git a/grammar/grammar.go b/grammar/grammar.go
index 60f1705..3268902 100644
--- a/grammar/grammar.go
+++ b/grammar/grammar.go
@@ -203,7 +203,7 @@ func (b *GrammarBuilder) genSymbolTableAndLexSpec(root *spec.RootNode) (*symbolT
 	for _, prod := range root.LexProductions {
 		if _, exist := symTab.toSymbol(prod.LHS); exist {
 			b.errs = append(b.errs, &verr.SpecError{
-				Cause:  semErrDuplicateSym,
+				Cause:  semErrDuplicateTerminal,
 				Detail: prod.LHS,
 				Row:    prod.Pos.Row,
 			})
@@ -280,7 +280,7 @@ func (b *GrammarBuilder) genSymbolTableAndLexSpec(root *spec.RootNode) (*symbolT
 	for _, fragment := range root.Fragments {
 		if _, exist := checkedFragments[fragment.LHS]; exist {
 			b.errs = append(b.errs, &verr.SpecError{
-				Cause:  semErrDuplicateSym,
+				Cause:  semErrDuplicateTerminal,
 				Detail: fragment.LHS,
 				Row:    fragment.Pos.Row,
 			})
@@ -432,10 +432,17 @@ func (b *GrammarBuilder) genProductionsAndActions(root *spec.RootNode, symTabAnd
 	prods.append(p)
 
 	for _, prod := range root.Productions {
-		_, err := symTab.registerNonTerminalSymbol(prod.LHS)
+		sym, err := symTab.registerNonTerminalSymbol(prod.LHS)
 		if err != nil {
 			return nil, err
 		}
+		if sym.isTerminal() {
+			b.errs = append(b.errs, &verr.SpecError{
+				Cause:  semErrDuplicateName,
+				Detail: prod.LHS,
+				Row:    prod.Pos.Row,
+			})
+		}
 	}
 
 	for _, prod := range root.Productions {
diff --git a/grammar/semantic_error.go b/grammar/semantic_error.go
index 4dcd313..2d722a8 100644
--- a/grammar/semantic_error.go
+++ b/grammar/semantic_error.go
@@ -21,7 +21,8 @@ var (
 	semErrNoProduction        = newSemanticError("a grammar needs at least one production")
 	semErrUndefinedSym        = newSemanticError("undefined symbol")
 	semErrDuplicateProduction = newSemanticError("duplicate production")
-	semErrDuplicateSym        = newSemanticError("duplicate symbol")
+	semErrDuplicateTerminal   = newSemanticError("duplicate terminal")
+	semErrDuplicateName       = newSemanticError("duplicate names are not allowed between terminals and non-terminals")
 	semErrDirInvalidName      = newSemanticError("invalid directive name")
 	semErrDirInvalidParam     = newSemanticError("invalid parameter")
 )