allow BindingPattern in FunctionRestParameter

src/compiler/checker.ts

@@ -28570,10 +28570,6 @@ namespace ts {
                         checkGrammarForDisallowedTrailingComma(parameters, Diagnostics.A_rest_parameter_or_binding_pattern_may_not_have_a_trailing_comma);
                     }
 
-                    if (isBindingPattern(parameter.name)) {
-                        return grammarErrorOnNode(parameter.name, Diagnostics.A_rest_element_cannot_contain_a_binding_pattern);
-                    }
-
                     if (parameter.questionToken) {
                         return grammarErrorOnNode(parameter.questionToken, Diagnostics.A_rest_parameter_cannot_be_optional);
                     }

src/compiler/transformers/es2015.ts

@@ -1340,8 +1340,8 @@ namespace ts {
          *                                          part of a constructor declaration with a
          *                                          synthesized call to `super`
          */
-        function shouldAddRestParameter(node: ParameterDeclaration | undefined, inConstructorWithSynthesizedSuper: boolean) {
-            return node && node.dotDotDotToken && node.name.kind === SyntaxKind.Identifier && !inConstructorWithSynthesizedSuper;
+        function shouldAddRestParameter(node: ParameterDeclaration | undefined, inConstructorWithSynthesizedSuper: boolean): node is ParameterDeclaration {
+            return !!(node && node.dotDotDotToken && !inConstructorWithSynthesizedSuper);
         }
 
         /**
@@ -1360,11 +1360,11 @@ namespace ts {
             }
 
             // `declarationName` is the name of the local declaration for the parameter.
-            const declarationName = getMutableClone(<Identifier>parameter!.name);
+            const declarationName = parameter.name.kind === SyntaxKind.Identifier ? getMutableClone(parameter.name) : createTempVariable(/*recordTempVariable*/ undefined);
             setEmitFlags(declarationName, EmitFlags.NoSourceMap);
 
             // `expressionName` is the name of the parameter used in expressions.
-            const expressionName = getSynthesizedClone(<Identifier>parameter!.name);
+            const expressionName = parameter.name.kind === SyntaxKind.Identifier ? getSynthesizedClone(parameter.name) : declarationName;
             const restIndex = node.parameters.length - 1;
             const temp = createLoopVariable();
 
@@ -1429,6 +1429,24 @@ namespace ts {
             setEmitFlags(forStatement, EmitFlags.CustomPrologue);
             startOnNewLine(forStatement);
             statements.push(forStatement);
+
+            if (parameter.name.kind !== SyntaxKind.Identifier) {
+                // do the actual destructuring of the rest parameter if necessary
+                statements.push(
+                    setEmitFlags(
+                        setTextRange(
+                            createVariableStatement(
+                                /*modifiers*/ undefined,
+                                createVariableDeclarationList(
+                                    flattenDestructuringBinding(parameter, visitor, context, FlattenLevel.All, expressionName),
+                                )
+                            ),
+                            parameter
+                        ),
+                        EmitFlags.CustomPrologue
+                    )
+                );
+            }
         }
 
         /**

tests/baselines/reference/iterableArrayPattern16.errors.txt

@@ -1,13 +1,10 @@
-tests/cases/conformance/es6/destructuring/iterableArrayPattern16.ts(1,17): error TS2501: A rest element cannot contain a binding pattern.
 tests/cases/conformance/es6/destructuring/iterableArrayPattern16.ts(2,5): error TS2345: Argument of type 'FooIterator' is not assignable to parameter of type '[Bar, Bar]'.
   Property '0' is missing in type 'FooIterator'.
 tests/cases/conformance/es6/destructuring/iterableArrayPattern16.ts(2,12): error TS2449: Class 'FooIteratorIterator' used before its declaration.
 
 
-==== tests/cases/conformance/es6/destructuring/iterableArrayPattern16.ts (3 errors) ====
+==== tests/cases/conformance/es6/destructuring/iterableArrayPattern16.ts (2 errors) ====
     function fun(...[a, b]: [Bar, Bar][]) { }
-                    ~~~~~~
-!!! error TS2501: A rest element cannot contain a binding pattern.
     fun(...new FooIteratorIterator);
         ~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type 'FooIterator' is not assignable to parameter of type '[Bar, Bar]'.

tests/baselines/reference/iterableArrayPattern17.errors.txt

@@ -1,9 +1,8 @@
-tests/cases/conformance/es6/destructuring/iterableArrayPattern17.ts(16,17): error TS2501: A rest element cannot contain a binding pattern.
 tests/cases/conformance/es6/destructuring/iterableArrayPattern17.ts(17,5): error TS2345: Argument of type 'FooIterator' is not assignable to parameter of type 'Bar'.
   Property 'x' is missing in type 'FooIterator'.
 
 
-==== tests/cases/conformance/es6/destructuring/iterableArrayPattern17.ts (2 errors) ====
+==== tests/cases/conformance/es6/destructuring/iterableArrayPattern17.ts (1 errors) ====
     class Bar { x }
     class Foo extends Bar { y }
     class FooIterator {
@@ -20,8 +19,6 @@ tests/cases/conformance/es6/destructuring/iterableArrayPattern17.ts(17,5): error
     }
 
     function fun(...[a, b]: Bar[]) { }
-                    ~~~~~~
-!!! error TS2501: A rest element cannot contain a binding pattern.
     fun(new FooIterator);
         ~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type 'FooIterator' is not assignable to parameter of type 'Bar'.

tests/baselines/reference/iterableArrayPattern25.errors.txt

@@ -1,11 +1,8 @@
-tests/cases/conformance/es6/destructuring/iterableArrayPattern25.ts(1,33): error TS2501: A rest element cannot contain a binding pattern.
 tests/cases/conformance/es6/destructuring/iterableArrayPattern25.ts(2,1): error TS2554: Expected 2 arguments, but got 1.
 
 
-==== tests/cases/conformance/es6/destructuring/iterableArrayPattern25.ts (2 errors) ====
+==== tests/cases/conformance/es6/destructuring/iterableArrayPattern25.ts (1 errors) ====
     function takeFirstTwoEntries(...[[k1, v1], [k2, v2]]) { }
-                                    ~~~~~~~~~~~~~~~~~~~~
-!!! error TS2501: A rest element cannot contain a binding pattern.
     takeFirstTwoEntries(new Map([["", 0], ["hello", 1]]));
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2554: Expected 2 arguments, but got 1.

tests/baselines/reference/iterableArrayPattern26.errors.txt

@@ -1,12 +1,9 @@
-tests/cases/conformance/es6/destructuring/iterableArrayPattern26.ts(1,33): error TS2501: A rest element cannot contain a binding pattern.
 tests/cases/conformance/es6/destructuring/iterableArrayPattern26.ts(2,21): error TS2345: Argument of type 'Map<string, number>' is not assignable to parameter of type '[string, number]'.
   Property '0' is missing in type 'Map<string, number>'.
 
 
-==== tests/cases/conformance/es6/destructuring/iterableArrayPattern26.ts (2 errors) ====
+==== tests/cases/conformance/es6/destructuring/iterableArrayPattern26.ts (1 errors) ====
     function takeFirstTwoEntries(...[[k1, v1], [k2, v2]]: [string, number][]) { }
-                                    ~~~~~~~~~~~~~~~~~~~~
-!!! error TS2501: A rest element cannot contain a binding pattern.
     takeFirstTwoEntries(new Map([["", 0], ["hello", 1]]));
                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type 'Map<string, number>' is not assignable to parameter of type '[string, number]'.

tests/baselines/reference/iterableArrayPattern28.errors.txt

@@ -1,4 +1,3 @@
-tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts(1,33): error TS2501: A rest element cannot contain a binding pattern.
 tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts(2,32): error TS2345: Argument of type '([string, number] | [string, boolean])[]' is not assignable to parameter of type 'ReadonlyArray<[string, number]>'.
   Types of property 'concat' are incompatible.
     Type '{ (...items: ConcatArray<[string, number] | [string, boolean]>[]): ([string, number] | [string, boolean])[]; (...items: ([string, number] | [string, boolean] | ConcatArray<[string, number] | [string, boolean]>)[]): ([string, number] | [string, boolean])[]; }' is not assignable to type '{ (...items: ConcatArray<[string, number]>[]): [string, number][]; (...items: ([string, number] | ConcatArray<[string, number]>)[]): [string, number][]; }'.
@@ -8,10 +7,8 @@ tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts(2,32): error
             Type 'boolean' is not assignable to type 'number'.
 
 
-==== tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts (2 errors) ====
+==== tests/cases/conformance/es6/destructuring/iterableArrayPattern28.ts (1 errors) ====
     function takeFirstTwoEntries(...[[k1, v1], [k2, v2]]: [string, number][]) { }
-                                    ~~~~~~~~~~~~~~~~~~~~
-!!! error TS2501: A rest element cannot contain a binding pattern.
     takeFirstTwoEntries(...new Map([["", 0], ["hello", true]]));
                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '([string, number] | [string, boolean])[]' is not assignable to parameter of type 'ReadonlyArray<[string, number]>'.

tests/baselines/reference/iterableArrayPattern29.errors.txt

@@ -1,12 +1,9 @@
-tests/cases/conformance/es6/destructuring/iterableArrayPattern29.ts(1,33): error TS2501: A rest element cannot contain a binding pattern.
 tests/cases/conformance/es6/destructuring/iterableArrayPattern29.ts(2,21): error TS2345: Argument of type '[string, boolean]' is not assignable to parameter of type '[string, number]'.
   Type 'boolean' is not assignable to type 'number'.
 
 
-==== tests/cases/conformance/es6/destructuring/iterableArrayPattern29.ts (2 errors) ====
+==== tests/cases/conformance/es6/destructuring/iterableArrayPattern29.ts (1 errors) ====
     function takeFirstTwoEntries(...[[k1, v1], [k2, v2]]: [string, number][]) { }
-                                    ~~~~~~~~~~~~~~~~~~~~
-!!! error TS2501: A rest element cannot contain a binding pattern.
     takeFirstTwoEntries(...new Map([["", true], ["hello", true]]));
                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '[string, boolean]' is not assignable to parameter of type '[string, number]'.

tests/baselines/reference/restParameterWithBindingPattern1.js

@@ -2,4 +2,10 @@
 function a(...{a, b}) { }
 
 //// [restParameterWithBindingPattern1.js]
-function a() { }
+function a() {
+    var _a = [];
+    for (var _i = 0; _i < arguments.length; _i++) {
+        _a[_i] = arguments[_i];
+    }
+    var a = _a.a, b = _a.b;
+}

tests/baselines/reference/restParameterWithBindingPattern2.sourcemap.txt

@@ -0,0 +1,90 @@
+===================================================================
+JsFile: restParameterWithBindingPattern2.js
+mapUrl: restParameterWithBindingPattern2.js.map
+sourceRoot: 
+sources: restParameterWithBindingPattern2.ts
+===================================================================
+-------------------------------------------------------------------
+emittedFile:tests/cases/compiler/restParameterWithBindingPattern2.js
+sourceFile:restParameterWithBindingPattern2.ts
+-------------------------------------------------------------------
+>>>function a() {
+1 >
+2 >^^^^^^^^^
+3 >         ^
+4 >          ^^^^^^^->
+1 >
+2 >function 
+3 >         a
+1 >Emitted(1, 1) Source(1, 1) + SourceIndex(0)
+2 >Emitted(1, 10) Source(1, 10) + SourceIndex(0)
+3 >Emitted(1, 11) Source(1, 11) + SourceIndex(0)
+---
+>>>    var _a = [];
+1->^^^^
+2 >    ^^^^^^^^^^^^
+3 >                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
+1->(
+2 >    ...[a, b]
+1->Emitted(2, 5) Source(1, 12) + SourceIndex(0)
+2 >Emitted(2, 17) Source(1, 21) + SourceIndex(0)
+---
+>>>    for (var _i = 0; _i < arguments.length; _i++) {
+1->^^^^^^^^^
+2 >         ^^^^^^^^^^
+3 >                   ^^
+4 >                     ^^^^^^^^^^^^^^^^^^^^^
+5 >                                          ^^
+6 >                                            ^^^^
+1->
+2 >         ...[a, b]
+3 >                   
+4 >                     ...[a, b]
+5 >                                          
+6 >                                            ...[a, b]
+1->Emitted(3, 10) Source(1, 12) + SourceIndex(0)
+2 >Emitted(3, 20) Source(1, 21) + SourceIndex(0)
+3 >Emitted(3, 22) Source(1, 12) + SourceIndex(0)
+4 >Emitted(3, 43) Source(1, 21) + SourceIndex(0)
+5 >Emitted(3, 45) Source(1, 12) + SourceIndex(0)
+6 >Emitted(3, 49) Source(1, 21) + SourceIndex(0)
+---
+>>>        _a[_i] = arguments[_i];
+1 >^^^^^^^^
+2 >        ^^^^^^^^^^^^^^^^^^^^^^^
+1 >
+2 >        ...[a, b]
+1 >Emitted(4, 9) Source(1, 12) + SourceIndex(0)
+2 >Emitted(4, 32) Source(1, 21) + SourceIndex(0)
+---
+>>>    }
+>>>    var a = _a[0], b = _a[1];
+1 >^^^^
+2 >    ^^^^
+3 >        ^^^^^^^^^
+4 >                 ^^
+5 >                   ^^^^^^^^^
+6 >                            ^
+1 >
+2 >    ...[
+3 >        a
+4 >                 , 
+5 >                   b
+6 >                            ]
+1 >Emitted(6, 5) Source(1, 12) + SourceIndex(0)
+2 >Emitted(6, 9) Source(1, 16) + SourceIndex(0)
+3 >Emitted(6, 18) Source(1, 17) + SourceIndex(0)
+4 >Emitted(6, 20) Source(1, 19) + SourceIndex(0)
+5 >Emitted(6, 29) Source(1, 20) + SourceIndex(0)
+6 >Emitted(6, 30) Source(1, 21) + SourceIndex(0)
+---
+>>>}
+1 >
+2 >^
+3 > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
+1 >) { 
+2 >}
+1 >Emitted(7, 1) Source(1, 25) + SourceIndex(0)
+2 >Emitted(7, 2) Source(1, 26) + SourceIndex(0)
+---
+>>>//# sourceMappingURL=restParameterWithBindingPattern2.js.map