Merge pull request #12177 from Microsoft/error-on-non-identifier-rest-in-destructuring-assignment

Error on non identifier rest in destructuring assignment

Author: sandersn

src/compiler/checker.ts

@@ -13941,7 +13941,12 @@ namespace ts {
                     error(name, Diagnostics.Type_0_has_no_property_1_and_no_string_index_signature, typeToString(objectLiteralType), declarationNameToString(name));
                 }
             }
-            else if (property.kind !== SyntaxKind.SpreadAssignment) {
+            else if (property.kind === SyntaxKind.SpreadAssignment) {
+                if (property.expression.kind !== SyntaxKind.Identifier) {
+                    error(property.expression, Diagnostics.An_object_rest_element_must_be_an_identifier);
+                }
+            }
+            else {
                 error(property, Diagnostics.Property_assignment_expected);
             }
         }

src/compiler/diagnosticMessages.json

@@ -1991,6 +1991,10 @@
         "category": "Error",
         "code": 2700
     },
+    "An object rest element must be an identifier.": {
+        "category": "Error",
+        "code": 2701
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

src/compiler/transformers/destructuring.ts

@@ -328,8 +328,9 @@ namespace ts {
                         bindingElements.push(p);
                     }
                 }
-                else if (i === properties.length - 1 && p.kind === SyntaxKind.SpreadAssignment) {
-                    Debug.assert((p as SpreadAssignment).expression.kind === SyntaxKind.Identifier);
+                else if (i === properties.length - 1 &&
+                         p.kind === SyntaxKind.SpreadAssignment &&
+                         p.expression.kind === SyntaxKind.Identifier) {
                     if (bindingElements.length) {
                         emitRestAssignment(bindingElements, value, location, target);
                         bindingElements = [];

tests/baselines/reference/objectRestNegative.errors.txt

@@ -1,9 +1,10 @@
 tests/cases/conformance/types/rest/objectRestNegative.ts(2,10): error TS2462: A rest element must be last in a destructuring pattern
 tests/cases/conformance/types/rest/objectRestNegative.ts(3,31): error TS2462: A rest element must be last in a destructuring pattern
 tests/cases/conformance/types/rest/objectRestNegative.ts(6,17): error TS2700: Rest types may only be created from object types.
+tests/cases/conformance/types/rest/objectRestNegative.ts(11,9): error TS2701: An object rest element must be an identifier.
 
 
-==== tests/cases/conformance/types/rest/objectRestNegative.ts (3 errors) ====
+==== tests/cases/conformance/types/rest/objectRestNegative.ts (4 errors) ====
     let o = { a: 1, b: 'no' };
     var { ...mustBeLast, a } = o;
              ~~~~~~~~~~
@@ -18,4 +19,9 @@ tests/cases/conformance/types/rest/objectRestNegative.ts(6,17): error TS2700: Re
 !!! error TS2700: Rest types may only be created from object types.
         return rest;
     }
+    
+    let rest: { b: string }
+    ({a, ...rest.b + rest.b} = o);
+            ~~~~~~~~~~~~~~~
+!!! error TS2701: An object rest element must be an identifier.
 

tests/baselines/reference/objectRestNegative.js

@@ -7,6 +7,9 @@ function generic<T extends { x, y }>(t: T) {
     let { x, ...rest } = t;
     return rest;
 }
+
+let rest: { b: string }
+({a, ...rest.b + rest.b} = o);
 
 
 //// [objectRestNegative.js]
@@ -25,3 +28,5 @@ function generic(t) {
     var x = t.x, rest = __rest(t, ["x"]);
     return rest;
 }
+var rest;
+(a = o.a, o, o);

tests/cases/conformance/types/rest/objectRestNegative.ts

@@ -6,3 +6,6 @@ function generic<T extends { x, y }>(t: T) {
     let { x, ...rest } = t;
     return rest;
 }
+
+let rest: { b: string }
+({a, ...rest.b + rest.b} = o);