Improved error reporting for predicates a bit.

lib/compiler.js

@@ -436,12 +436,16 @@ PEG.Grammar.ZeroOrMore.prototype.compile = function(resultVar) {
 };
 
 PEG.Grammar.NotPredicate.prototype.compile = function(resultVar) {
-  var savedPosVar         = PEG.Compiler.generateUniqueIdentifier("savedPos");
-  var expressionResultVar = PEG.Compiler.generateUniqueIdentifier("result");
+  var savedPosVar                 = PEG.Compiler.generateUniqueIdentifier("savedPos");
+  var savedReportMatchFailuresVar = PEG.Compiler.generateUniqueIdentifier("savedReportMatchFailuresVar");
+  var expressionResultVar         = PEG.Compiler.generateUniqueIdentifier("result");
 
   return PEG.Compiler.formatCode(
     "var ${savedPosVar} = this._pos;",
+    "var ${savedReportMatchFailuresVar} = context.reportMatchFailures;",
+    "context.reportMatchFailures = false;",
     "${expressionCode}",
+    "context.reportMatchFailures = ${savedReportMatchFailuresVar};",
     "if (${expressionResultVar} === null) {",
     "  var ${resultVar} = '';",
     "} else {",
@@ -449,10 +453,11 @@ PEG.Grammar.NotPredicate.prototype.compile = function(resultVar) {
     "  this._pos = ${savedPosVar};",
     "}",
     {
-      expressionCode:      this._expression.compile(expressionResultVar),
-      expressionResultVar: expressionResultVar,
-      savedPosVar:         savedPosVar,
-      resultVar:           resultVar
+      expressionCode:              this._expression.compile(expressionResultVar),
+      expressionResultVar:         expressionResultVar,
+      savedPosVar:                 savedPosVar,
+      savedReportMatchFailuresVar: savedReportMatchFailuresVar,
+      resultVar:                   resultVar
     }
   );
 };

test/compiler-test.js

@@ -379,6 +379,20 @@ test("error messages", function() {
     'Expected "c" but "d" found.'
   );
 
+  var notPredicateParser = PEG.buildParser('start: !"a" "b"');
+  doesNotParseWithMessage(
+    notPredicateParser,
+    "c",
+    'Expected "b" but "c" found.'
+  );
+
+  var andPredicateParser = PEG.buildParser('start: &"a" [a-b]');
+  doesNotParseWithMessage(
+    andPredicateParser,
+    "c",
+    'Expected end of input but "c" found.'
+  );
+
   var emptyParser = PEG.buildParser('start: ');
   doesNotParseWithMessage(
     emptyParser,