Report duplicate labels as errors

Resolves #270.

lib/compiler/index.js

@@ -19,17 +19,18 @@ var compiler = {
    */
   passes: {
     check: {
-      reportMissingRules:   require("./passes/report-missing-rules"),
-      reportDuplicateRules: require("./passes/report-duplicate-rules"),
-      reportLeftRecursion:  require("./passes/report-left-recursion"),
-      reportInfiniteLoops:  require("./passes/report-infinite-loops")
+      reportMissingRules:    require("./passes/report-missing-rules"),
+      reportDuplicateRules:  require("./passes/report-duplicate-rules"),
+      reportDuplicateLabels: require("./passes/report-duplicate-labels"),
+      reportLeftRecursion:   require("./passes/report-left-recursion"),
+      reportInfiniteLoops:   require("./passes/report-infinite-loops")
     },
     transform: {
-      removeProxyRules:     require("./passes/remove-proxy-rules")
+      removeProxyRules:      require("./passes/remove-proxy-rules")
     },
     generate: {
-      generateBytecode:     require("./passes/generate-bytecode"),
-      generateJS:           require("./passes/generate-js")
+      generateBytecode:      require("./passes/generate-bytecode"),
+      generateJS:            require("./passes/generate-js")
     }
   },
 

lib/compiler/passes/report-duplicate-labels.js

@@ -0,0 +1,54 @@
+"use strict";
+
+var GrammarError = require("../../grammar-error"),
+    arrays       = require("../../utils/arrays"),
+    objects      = require("../../utils/objects"),
+    visitor      = require("../visitor");
+
+/* Checks that each label is defined only once within each scope. */
+function reportDuplicateLabels(ast) {
+  function checkExpressionWithClonedEnv(node, env) {
+    check(node.expression, objects.clone(env));
+  }
+
+  var check = visitor.build({
+    rule: function(node) {
+      check(node.expression, { });
+    },
+
+    choice: function(node, env) {
+      arrays.each(node.alternatives, function(alternative) {
+        check(alternative, objects.clone(env));
+      });
+    },
+
+    action: checkExpressionWithClonedEnv,
+
+    labeled: function(node, env) {
+      if (env.hasOwnProperty(node.label)) {
+        throw new GrammarError(
+          "Label \"" + node.label + "\" is already defined "
+            + "at line " + env[node.label].start.line + ", "
+            + "column " + env[node.label].start.column + ".",
+          node.location
+        );
+      }
+
+      check(node.expression, env);
+
+      env[node.label] = node.location;
+    },
+
+    text:         checkExpressionWithClonedEnv,
+    simple_and:   checkExpressionWithClonedEnv,
+    simple_not:   checkExpressionWithClonedEnv,
+    optional:     checkExpressionWithClonedEnv,
+    zero_or_more: checkExpressionWithClonedEnv,
+    one_or_more:  checkExpressionWithClonedEnv,
+    group:        checkExpressionWithClonedEnv
+  });
+
+  check(ast);
+}
+
+module.exports = reportDuplicateLabels;

package.json

@@ -28,6 +28,7 @@
     "lib/compiler/passes/generate-js.js",
     "lib/compiler/passes/remove-proxy-rules.js",
     "lib/compiler/passes/report-duplicate-rules.js",
+    "lib/compiler/passes/report-duplicate-labels.js",
     "lib/compiler/passes/report-infinite-loops.js",
     "lib/compiler/passes/report-left-recursion.js",
     "lib/compiler/passes/report-missing-rules.js",

spec/index.html

@@ -11,6 +11,7 @@
     <script src="unit/compiler/passes/helpers.js"></script>
     <script src="unit/compiler/passes/report-missing-rules.spec.js"></script>
     <script src="unit/compiler/passes/report-duplicate-rules.spec.js"></script>
+    <script src="unit/compiler/passes/report-duplicate-labels.spec.js"></script>
     <script src="unit/compiler/passes/report-left-recursion.spec.js"></script>
     <script src="unit/compiler/passes/report-infinite-loops.spec.js"></script>
     <script src="unit/compiler/passes/remove-proxy-rules.spec.js"></script>

spec/unit/compiler/passes/report-duplicate-labels.spec.js

@@ -0,0 +1,59 @@
+/* global peg */
+
+"use strict";
+
+describe("compiler pass |reportDuplicateLabels|", function() {
+  var pass = peg.compiler.passes.check.reportDuplicateLabels;
+
+  describe("in a sequence", function() {
+    it("reports labels duplicate with labels of preceding elements", function() {
+      expect(pass).toReportError('start = a:"a" a:"a"', {
+        message:  'Label "a" is already defined at line 1, column 9.',
+        location: {
+          start: { offset: 14, line: 1, column: 15 },
+          end:   { offset: 19, line: 1, column: 20 }
+        }
+      });
+    });
+
+    it("doesn't report labels duplicate with labels in subexpressions", function() {
+      expect(pass).not.toReportError('start = ("a" / a:"a" / "a") a:"a"');
+      expect(pass).not.toReportError('start = (a:"a" { }) a:"a"');
+      expect(pass).not.toReportError('start = ("a" a:"a" "a") a:"a"');
+      expect(pass).not.toReportError('start = b:(a:"a") a:"a"');
+      expect(pass).not.toReportError('start = $(a:"a") a:"a"');
+      expect(pass).not.toReportError('start = &(a:"a") a:"a"');
+      expect(pass).not.toReportError('start = !(a:"a") a:"a"');
+      expect(pass).not.toReportError('start = (a:"a")? a:"a"');
+      expect(pass).not.toReportError('start = (a:"a")* a:"a"');
+      expect(pass).not.toReportError('start = (a:"a")+ a:"a"');
+      expect(pass).not.toReportError('start = (a:"a") a:"a"');
+    });
+  });
+
+  describe("in a choice", function() {
+    it("doesn't report labels duplicate with labels of preceding alternatives", function() {
+      expect(pass).not.toReportError('start = a:"a" / a:"a"');
+    });
+  });
+
+  describe("in outer sequence", function() {
+    it("reports labels duplicate with labels of preceding elements", function() {
+      expect(pass).toReportError('start = a:"a" (a:"a")', {
+        message:  'Label "a" is already defined at line 1, column 9.',
+        location: {
+          start: { offset: 15, line: 1, column: 16 },
+          end:   { offset: 20, line: 1, column: 21 }
+        }
+      });
+    });
+
+    it("doesn't report labels duplicate with the label of the current element", function() {
+      expect(pass).not.toReportError('start = a:(a:"a")');
+    });
+
+    it("doesn't report labels duplicate with labels of following elements", function() {
+      expect(pass).not.toReportError('start = (a:"a") a:"a"');
+    });
+  });
+});