Bug 885463 - Warn about 'yield' without operand. r=Waldo.

js/src/frontend/Parser.cpp

@@ -4425,6 +4425,11 @@ Parser<ParseHandler>::returnStatementOrYieldExpression()
         (isYield && (next == TOK_YIELD || next == TOK_RB || next == TOK_RP ||
                      next == TOK_COLON || next == TOK_COMMA)))
     {
+        if (isYield) {
+            if (!reportWithOffset(ParseWarning, false, pos().begin, JSMSG_YIELD_WITHOUT_OPERAND))
+                return null();
+        }
+
         exprNode = null();
         if (!isYield)
             pc->funHasReturnVoid = true;

js/src/jit-test/lib/asserts.js

@@ -38,3 +38,64 @@ if (typeof assertThrowsValue === 'undefined') {
         throw new Error(fullmsg);
     };
 }
+
+if (typeof assertWarning === 'undefined') {
+    var assertWarning = function assertWarning(f, errorClass, msg) {
+        var hadWerror = options().split(",").indexOf("werror") !== -1;
+
+        // Ensure the "werror" option is disabled.
+        if (hadWerror)
+            options("werror");
+
+        try {
+            f();
+        } catch (exc) {
+            if (hadWerror)
+                options("werror");
+
+            // print() rather than throw a different exception value, in case
+            // the caller wants exc.stack.
+            if (msg)
+                print("assertWarning: " + msg);
+            print("assertWarning: Unexpected exception calling " + f +
+                  " with warnings-as-errors disabled");
+            throw exc;
+        }
+
+        // Enable the "werror" option.
+        options("werror");
+
+        try {
+            assertThrowsInstanceOf(f, errorClass, msg);
+        } catch (exc) {
+            if (msg)
+                print("assertWarning: " + msg);
+            throw exc;
+        } finally {
+            if (!hadWerror)
+                options("werror");
+        }
+    };
+}
+
+if (typeof assertNoWarning === 'undefined') {
+    var assertNoWarning = function assertWarning(f, msg) {
+        // Ensure the "werror" option is enabled.
+        var hadWerror = options().split(",").indexOf("werror") !== -1;
+        if (!hadWerror)
+            options("werror");
+
+        try {
+            f();
+        } catch (exc) {
+            if (msg)
+                print("assertNoWarning: " + msg);
+            print("assertNoWarning: Unexpected exception calling " + f +
+                  "with warnings-as-errors enabled");
+            throw exc;
+        } finally {
+            if (!hadWerror)
+                options("werror");
+        }
+    };
+}

js/src/jit-test/tests/parser/yield-without-operand.js

@@ -0,0 +1,22 @@
+// yield without an operand causes a warning. See bug 885463.
+
+load(libdir + "asserts.js");
+
+assertWarning(() => Function("yield"), SyntaxError,
+             "yield followed by EOF should cause a warning");
+assertWarning(() => Function("yield;"), SyntaxError,
+             "yield followed by semicolon should cause a warning");
+assertWarning(() => Function("yield\n  print('ok');"), SyntaxError,
+             "yield followed by newline should cause a warning");
+
+assertWarning(() => eval("(function () { yield; })"), SyntaxError,
+             "yield followed by semicolon in eval code should cause a warning");
+assertWarning(() => eval("(function () { yield })"), SyntaxError,
+             "yield followed by } in eval code should cause a warning");
+
+assertNoWarning(() => Function("yield 0;"),
+                "yield with an operand should be fine");
+assertNoWarning(() => Function("yield 0"),
+                "yield with an operand should be fine, even without a semicolon");
+
+print("\npassed - all those warnings are normal and there's no real way to suppress them");

js/src/js.msg

@@ -322,7 +322,7 @@ MSG_DEF(JSMSG_INVALID_FOR_IN_INIT,    268, 0, JSEXN_SYNTAXERR, "for-in loop let
 MSG_DEF(JSMSG_CLEARED_SCOPE,          269, 0, JSEXN_TYPEERR, "attempt to run compile-and-go script on a cleared scope")
 MSG_DEF(JSMSG_MALFORMED_ESCAPE,       270, 1, JSEXN_SYNTAXERR, "malformed {0} character escape sequence")
 MSG_DEF(JSMSG_BAD_GENEXP_BODY,        271, 1, JSEXN_SYNTAXERR, "illegal use of {0} in generator expression")
-MSG_DEF(JSMSG_UNUSED272,              272, 0, JSEXN_NONE, "")
+MSG_DEF(JSMSG_YIELD_WITHOUT_OPERAND,  272, 0, JSEXN_SYNTAXERR, "yield without a value is deprecated, and illegal in ES6 (use 'yield undefined' instead)")
 MSG_DEF(JSMSG_UNNAMED_FUNCTION_STMT,  273, 0, JSEXN_SYNTAXERR, "function statement requires a name")
 MSG_DEF(JSMSG_CCW_REQUIRED,           274, 1, JSEXN_TYPEERR, "{0}: argument must be an object from a different compartment")
 MSG_DEF(JSMSG_DEBUG_BAD_RESUMPTION,   275, 0, JSEXN_TYPEERR, "debugger resumption value must be undefined, {throw: val}, {return: val}, or null")