Handle the scenario when let [a=undefined]=[]

Author: sheetalkamat

src/compiler/checker.ts

@@ -2885,11 +2885,7 @@ namespace ts {
         // pattern. Otherwise, it is the type any.
         function getTypeFromBindingElement(element: BindingElement, includePatternInType?: boolean, reportErrors?: boolean): Type {
             if (element.initializer) {
-                const type = checkExpressionCached(element.initializer);
-                if (reportErrors) {
-                    reportErrorsFromWidening(element, type);
-                }
-                return getWidenedType(type);
+                return checkExpressionCached(element.initializer);
             }
             if (isBindingPattern(element.name)) {
                 return getTypeFromBindingPattern(<BindingPattern>element.name, includePatternInType, reportErrors);

tests/baselines/reference/noImplicitAnyDestructuringVarDeclaration.errors.txt

@@ -19,9 +19,10 @@ tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts(9,6): error TS7
 tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts(9,26): error TS7031: Binding element 'b4' implicitly has an 'any' type.
 tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts(9,46): error TS7005: Variable 'c4' implicitly has an 'any' type.
 tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts(9,62): error TS7005: Variable 'd4' implicitly has an 'any' type.
+tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts(11,6): error TS7031: Binding element 'a5' implicitly has an 'any' type.
 
 
-==== tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts (21 errors) ====
+==== tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts (22 errors) ====
     var [a], {b}, c, d; // error
         ~~~
 !!! error TS1182: A destructuring declaration must have an initializer.
@@ -72,4 +73,8 @@ tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts(9,62): error TS
                                                  ~~
 !!! error TS7005: Variable 'c4' implicitly has an 'any' type.
                                                                  ~~
-!!! error TS7005: Variable 'd4' implicitly has an 'any' type.
+!!! error TS7005: Variable 'd4' implicitly has an 'any' type.
+    
+    var [a5 = undefined] = []; // error
+         ~~
+!!! error TS7031: Binding element 'a5' implicitly has an 'any' type.

tests/baselines/reference/noImplicitAnyDestructuringVarDeclaration.js

@@ -7,11 +7,14 @@ var [a2]: [any], {b2}: { b2: any }, c2: any, d2: any;
 
 var {b3}: { b3 }, c3: { b3 }; // error in type instead
 
-var [a4] = [undefined], {b4} = { b4: null }, c4 = undefined, d4 = null; // error
+var [a4] = [undefined], {b4} = { b4: null }, c4 = undefined, d4 = null; // error
+
+var [a5 = undefined] = []; // error
 
 //// [noImplicitAnyDestructuringVarDeclaration.js]
 var a = (void 0)[0], b = (void 0).b, c, d; // error
 var _a = (void 0)[0], a1 = _a === void 0 ? undefined : _a, _b = (void 0).b1, b1 = _b === void 0 ? null : _b, c1 = undefined, d1 = null; // error
 var a2 = (void 0)[0], b2 = (void 0).b2, c2, d2;
 var b3 = (void 0).b3, c3; // error in type instead
 var a4 = [undefined][0], b4 = { b4: null }.b4, c4 = undefined, d4 = null; // error
+var _c = [][0], a5 = _c === void 0 ? undefined : _c; // error

tests/cases/compiler/noImplicitAnyDestructuringVarDeclaration.ts

@@ -7,4 +7,6 @@ var [a2]: [any], {b2}: { b2: any }, c2: any, d2: any;
 
 var {b3}: { b3 }, c3: { b3 }; // error in type instead
 
-var [a4] = [undefined], {b4} = { b4: null }, c4 = undefined, d4 = null; // error
+var [a4] = [undefined], {b4} = { b4: null }, c4 = undefined, d4 = null; // error
+
+var [a5 = undefined] = []; // error