Experimental fix for ohmjs#21

src/MatchResult.js

@@ -11,16 +11,6 @@ var nodes = require('./nodes');
 var util = require('./util');
 var Interval = require('./Interval');
 
-// --------------------------------------------------------------------
-// Private stuff
-// --------------------------------------------------------------------
-
-// Create a short error message for an error that occurred during matching.
-function getShortMatchErrorMessage(pos, source, detail) {
-  var errorInfo = util.getLineAndColumn(source, pos);
-  return 'Line ' + errorInfo.lineNum + ', col ' + errorInfo.colNum + ': ' + detail;
-}
-
 // ----------------- MatchFailure -----------------
 
 function MatchResult(state) {
@@ -147,10 +137,7 @@ function MatchFailure(state) {
       return 'match failed at position ' + this.getRightmostFailurePosition();
     }
     var detail = 'expected ' + this.getExpectedText();
-    return getShortMatchErrorMessage(
-        this.getRightmostFailurePosition(),
-        this.state.inputStream.source,
-        detail);
+    return util.getShortLineAndColumnMessage(this.state.inputStream.source, this.getRightmostFailurePosition()) + detail;
   });
 }
 inherits(MatchFailure, MatchResult);

src/errors.js

@@ -5,6 +5,7 @@
 // --------------------------------------------------------------------
 
 var Namespace = require('./Namespace');
+var util = require('./util');
 
 // --------------------------------------------------------------------
 // Private stuff
@@ -34,11 +35,40 @@ function intervalSourcesDontMatch() {
 
 function grammarSyntaxError(matchFailure) {
   var e = new Error();
-  Object.defineProperty(e, 'message', {get: function() { return matchFailure.message; }});
-  Object.defineProperty(e, 'shortMessage', {get: function() {
-    return 'Expected ' + matchFailure.getExpectedText();
-  }});
+
   e.interval = matchFailure.getInterval();
+
+  var message;
+  var shortMessage;
+
+  var source = matchFailure.state.inputStream.source;
+
+  // Iterate through the failures, in an attempt to produce a more relevant error message
+  var reason = null;
+
+  var failures = matchFailure.getRightmostFailures();
+  for(var i = 0; i < failures.length; i++) {
+    var failure = failures[i];
+    if (failure.getPExpr().ruleName === 'escapeChar'){
+      // Failure to match an escape sequence, therefore the grammar contains an invalid escape sequence.
+      var escapeSequence = source.substr(matchFailure.getRightmostFailurePosition(),2);
+      var reason = "Invalid escape sequence \"" + escapeSequence + "\"";
+      break;
+    }
+  }
+
+  if (reason) {
+      // Use the more relevant reason an the error message
+      message = util.getLineAndColumnMessage(source, matchFailure.getRightmostFailurePosition()) + reason; 
+      shortMessage = util.getShortLineAndColumnMessage(source, matchFailure.getRightmostFailurePosition()) + reason;
+  } else {
+      // Use the default parse failure message for the error. This is usually sufficient.
+      message = matchFailure.message;
+      shortMessage = 'Expected ' + matchFailure.getExpectedText();
+  }
+
+  Object.defineProperty(e, 'message', {get: function() { return message; }});
+  Object.defineProperty(e, 'shortMessage', {get: function() { return shortMessage; }});
   return e;
 }
 

src/util.js

@@ -146,3 +146,8 @@ exports.getLineAndColumnMessage = function(str, offset /* ...ranges */) {
   }
   return sb.contents();
 };
+
+exports.getShortLineAndColumnMessage = function(str, offset){
+  var errorInfo = exports.getLineAndColumn(str, offset);
+  return 'Line ' + errorInfo.lineNum + ', col ' + errorInfo.colNum + ': ';
+}

visualizer/index.js

@@ -26,6 +26,13 @@
     var grammar;
     var err;
 
+    try {
+      ohm.grammar(source);
+    } catch (ex) {
+      err = ex;
+    }
+
+    /*
     if (matchResult.succeeded()) {
       var ns = {};
       try {
@@ -43,7 +50,7 @@
         shortMessage: matchResult.shortMessage,
         interval: matchResult.getInterval()
       };
-    }
+    }*/
     return {
       matchResult: matchResult,
       grammar: grammar,