Bug 1384299 - Provide better error message when errornous syntax possibly match "yield SOMETHING" outside generators. r=till

js/src/frontend/Parser.cpp

@@ -2929,6 +2929,10 @@ Parser<ParseHandler, CharT>::matchOrInsertSemicolonHelper(TokenStream::Modifier
             error(JSMSG_AWAIT_OUTSIDE_ASYNC);
             return false;
         }
+        if (!yieldExpressionsSupported() && tokenStream.currentToken().type == TOK_YIELD) {
+            error(JSMSG_YIELD_OUTSIDE_GENERATOR);
+            return false;
+        }
 
         /* Advance the scanner for proper error location reporting. */
         tokenStream.consumeKnownToken(tt, modifier);

js/src/js.msg

@@ -353,6 +353,7 @@ MSG_DEF(JSMSG_WHILE_AFTER_DO,          0, JSEXN_SYNTAXERR, "missing while after
 MSG_DEF(JSMSG_YIELD_IN_ARROW,          0, JSEXN_SYNTAXERR, "arrow function may not contain yield")
 MSG_DEF(JSMSG_YIELD_IN_DEFAULT,        0, JSEXN_SYNTAXERR, "yield in default expression")
 MSG_DEF(JSMSG_YIELD_IN_METHOD,         0, JSEXN_SYNTAXERR, "non-generator method definitions may not contain yield")
+MSG_DEF(JSMSG_YIELD_OUTSIDE_GENERATOR, 0, JSEXN_SYNTAXERR, "yield expression is only valid in generators")
 MSG_DEF(JSMSG_BAD_COLUMN_NUMBER,       0, JSEXN_RANGEERR, "column number out of range")
 MSG_DEF(JSMSG_COMPUTED_NAME_IN_PATTERN,0, JSEXN_SYNTAXERR, "computed property names aren't supported in this destructuring declaration")
 MSG_DEF(JSMSG_DEFAULT_IN_PATTERN,      0, JSEXN_SYNTAXERR, "destructuring defaults aren't supported in this destructuring declaration")

js/src/tests/ecma_6/Generators/yield-error.js

@@ -0,0 +1,32 @@
+var BUGNUMBER = 1384299;
+var summary = "yield outside of generators should provide better error";
+
+print(BUGNUMBER + ": " + summary);
+
+let caught = false;
+try {
+    eval("yield 10");
+} catch(e) {
+    assertEq(e.message, "yield expression is only valid in generators");
+    caught = true;
+}
+assertEq(caught, true);
+
+try {
+    eval("function f() { yield 10; }");
+} catch(e) {
+    assertEq(e.message, "yield expression is only valid in generators");
+    caught = true;
+}
+assertEq(caught, true);
+
+try {
+    eval("async function f() { yield 10; }");
+} catch(e) {
+    assertEq(e.message, "yield expression is only valid in generators");
+    caught = true;
+}
+assertEq(caught, true);
+
+if (typeof reportCompare === "function")
+    reportCompare(true, true);