Error on rest parameter with trailing comma

Author: Andy Hanson

src/compiler/checker.ts

@@ -26093,6 +26093,9 @@ namespace ts {
                     if (i !== (parameterCount - 1)) {
                         return grammarErrorOnNode(parameter.dotDotDotToken, Diagnostics.A_rest_parameter_must_be_last_in_a_parameter_list);
                     }
+                    if (parameters.hasTrailingComma) {
+                        return grammarErrorOnNode(parameter.dotDotDotToken, Diagnostics.A_rest_parameter_may_not_have_a_trailing_comma);
+                    }
 
                     if (isBindingPattern(parameter.name)) {
                         return grammarErrorOnNode(parameter.name, Diagnostics.A_rest_element_cannot_contain_a_binding_pattern);

src/compiler/diagnosticMessages.json

@@ -27,6 +27,10 @@
         "category": "Error",
         "code": 1012
     },
+    "A rest parameter may not have a trailing comma.": {
+        "category": "Error",
+        "code": 1013
+    },
     "A rest parameter must be last in a parameter list.": {
         "category": "Error",
         "code": 1014

tests/baselines/reference/trailingCommasInFunctionParametersAndArguments.errors.txt

@@ -0,0 +1,34 @@
+tests/cases/conformance/es7/trailingCommasInFunctionParametersAndArguments.ts(5,13): error TS1013: A rest parameter may not have a trailing comma.
+
+
+==== tests/cases/conformance/es7/trailingCommasInFunctionParametersAndArguments.ts (1 errors) ====
+    function f1(x,) {}
+    
+    f1(1,);
+    
+    function f2(...args,) {}
+                ~~~
+!!! error TS1013: A rest parameter may not have a trailing comma.
+    
+    f2(...[],);
+    
+    // Not confused by overloads
+    declare function f3(x, ): number;
+    declare function f3(x, y,): string;
+    
+    <number>f3(1,);
+    <string>f3(1, 2,);
+    
+    // Works for constructors too
+    class X {
+        constructor(a,) { }
+        // See trailingCommasInGetter.ts
+        set x(value,) { }
+    }
+    interface Y {
+        new(x,);
+        (x,);
+    }
+    
+    new X(1,);
+