Add index validation for @ references

lib/lrama/grammar/rule_builder.rb

@@ -245,13 +245,12 @@ def numberize_references
               ref.index = ref.number
             end
 
-            # TODO: Need to check index of @ too?
-            next if ref.type == :at
-
             if ref.index
               # TODO: Prohibit $0 even so Bison allows it?
               # See: https://www.gnu.org/software/bison/manual/html_node/Actions.html
               token.invalid_ref(ref, "Can not refer following component. #{ref.index} >= #{i}.") if ref.index >= i
+              next if ref.type == :at
+
               rhs[ref.index - 1].referred = true
             end
           end

spec/fixtures/integration/contains_at_reference.y

@@ -14,7 +14,7 @@ static int yyerror(YYLTYPE *loc, const char *str);
 
 %%
 
-program : /* empty */ { (void)@1; }
+program : /* empty */ { (void)@0; }
         ;
 
 %%

spec/lrama/grammar/rule_builder_spec.rb

@@ -283,6 +283,41 @@
       end
     end
 
+    context "location variables in mid action rule refer to following component" do
+      let(:text) { "class : keyword_class { @3; } tSTRING keyword_end { $class = $1; }" }
+      let(:grammar_file) { Lrama::Lexer::GrammarFile.new(path, text) }
+      let(:location_1) { Lrama::Lexer::Location.new(grammar_file: grammar_file, first_line: 1, first_column: 0, last_line: 1, last_column: 5) }
+      let(:location_2) { Lrama::Lexer::Location.new(grammar_file: grammar_file, first_line: 1, first_column: 8, last_line: 1, last_column: 21) }
+      let(:location_3) { Lrama::Lexer::Location.new(grammar_file: grammar_file, first_line: 1, first_column: 23, last_line: 1, last_column: 28) }
+      let(:location_4) { Lrama::Lexer::Location.new(grammar_file: grammar_file, first_line: 1, first_column: 30, last_line: 1, last_column: 37) }
+      let(:location_5) { Lrama::Lexer::Location.new(grammar_file: grammar_file, first_line: 1, first_column: 38, last_line: 1, last_column: 49) }
+      let(:location_6) { Lrama::Lexer::Location.new(grammar_file: grammar_file, first_line: 1, first_column: 51, last_line: 1, last_column: 65) }
+      let(:token_1) { Lrama::Lexer::Token::Ident.new(s_value: "class", location: location_1) }
+      let(:token_2) { Lrama::Lexer::Token::Ident.new(s_value: "keyword_class", location: location_2) }
+      let(:token_3) { Lrama::Lexer::Token::UserCode.new(s_value: " @3; ", location: location_3) }
+      let(:token_4) { Lrama::Lexer::Token::Ident.new(s_value: "tSTRING", location: location_4) }
+      let(:token_5) { Lrama::Lexer::Token::Ident.new(s_value: "keyword_end", location: location_5) }
+      let(:token_6) { Lrama::Lexer::Token::UserCode.new(s_value: " $class = $1; ", location: location_6) }
+
+      it "raises error" do
+        rule_builder.lhs = token_1
+        rule_builder.add_rhs(token_2)
+        rule_builder.user_code = token_3
+        rule_builder.add_rhs(token_4)
+        rule_builder.add_rhs(token_5)
+        rule_builder.user_code = token_6
+        rule_builder.complete_input
+
+        expected = <<~TEXT
+          parse.y:1:24: Can not refer following component. 3 >= 2.
+             1 | class : keyword_class { @3; } tSTRING keyword_end { $class = $1; }
+               |                         ^~
+        TEXT
+
+        expect { rule_builder.send(:preprocess_references) }.to raise_error(expected)
+      end
+    end
+
     context "variables refer with wrong name" do
       let(:text) { "class : keyword_class tSTRING keyword_end { $classes = $1; }" }
       let(:grammar_file) { Lrama::Lexer::GrammarFile.new(path, text) }