Merge pull request microsoft#32035 from microsoft/fixTupleDestructuringControlFlow

Fix tuple destructuring control flow analysis

Author: ahejlsberg

src/compiler/checker.ts

@@ -14440,7 +14440,7 @@ namespace ts {
             if (propType) {
                 return propType;
             }
-            if (everyType(type, isTupleType) && !everyType(type, t => !(<TupleTypeReference>t).target.hasRestElement)) {
+            if (everyType(type, isTupleType)) {
                 return mapType(type, t => getRestTypeOfTupleType(<TupleTypeReference>t) || undefinedType);
             }
             return undefined;

tests/baselines/reference/destructuringControlFlow.errors.txt

@@ -1,9 +1,10 @@
 tests/cases/conformance/es6/destructuring/destructuringControlFlow.ts(31,8): error TS2339: Property 'x' does not exist on type 'Number'.
 tests/cases/conformance/es6/destructuring/destructuringControlFlow.ts(32,9): error TS2339: Property 'x' does not exist on type 'Number'.
 tests/cases/conformance/es6/destructuring/destructuringControlFlow.ts(33,9): error TS2537: Type 'Number' has no matching index signature for type 'string'.
+tests/cases/conformance/es6/destructuring/destructuringControlFlow.ts(40,1): error TS2532: Object is possibly 'undefined'.
 
 
-==== tests/cases/conformance/es6/destructuring/destructuringControlFlow.ts (3 errors) ====
+==== tests/cases/conformance/es6/destructuring/destructuringControlFlow.ts (4 errors) ====
     function f1(obj: { a?: string }) {
         if (obj.a) {
             obj = {};
@@ -44,4 +45,12 @@ tests/cases/conformance/es6/destructuring/destructuringControlFlow.ts(33,9): err
             ~~~~~~~~
 !!! error TS2537: Type 'Number' has no matching index signature for type 'string'.
     }
+    
+    // Repro from #31770
+    
+    type KeyValue = [string, string?];
+    let [key, value]: KeyValue = ["foo"];
+    value.toUpperCase();  // Error
+    ~~~~~
+!!! error TS2532: Object is possibly 'undefined'.
 

tests/baselines/reference/destructuringControlFlow.js

@@ -33,6 +33,12 @@ function f4() {
     ({ ["x"]: x } = 0);  // Error
     ({ ["x" + ""]: x } = 0);  // Errpr
 }
+
+// Repro from #31770
+
+type KeyValue = [string, string?];
+let [key, value]: KeyValue = ["foo"];
+value.toUpperCase();  // Error
 
 
 //// [destructuringControlFlow.js]
@@ -69,3 +75,5 @@ function f4() {
     (x = 0["x"]); // Error
     (_a = "x" + "", x = 0[_a]); // Errpr
 }
+var _a = ["foo"], key = _a[0], value = _a[1];
+value.toUpperCase(); // Error

tests/baselines/reference/destructuringControlFlow.symbols

@@ -122,3 +122,16 @@ function f4() {
 >x : Symbol(x, Decl(destructuringControlFlow.ts, 29, 7))
 }
 
+// Repro from #31770
+
+type KeyValue = [string, string?];
+>KeyValue : Symbol(KeyValue, Decl(destructuringControlFlow.ts, 33, 1))
+
+let [key, value]: KeyValue = ["foo"];
+>key : Symbol(key, Decl(destructuringControlFlow.ts, 38, 5))
+>value : Symbol(value, Decl(destructuringControlFlow.ts, 38, 9))
+>KeyValue : Symbol(KeyValue, Decl(destructuringControlFlow.ts, 33, 1))
+
+value.toUpperCase();  // Error
+>value : Symbol(value, Decl(destructuringControlFlow.ts, 38, 9))
+

tests/baselines/reference/destructuringControlFlow.types

@@ -158,3 +158,20 @@ function f4() {
 >0 : 0
 }
 
+// Repro from #31770
+
+type KeyValue = [string, string?];
+>KeyValue : [string, (string | undefined)?]
+
+let [key, value]: KeyValue = ["foo"];
+>key : string
+>value : string | undefined
+>["foo"] : [string]
+>"foo" : "foo"
+
+value.toUpperCase();  // Error
+>value.toUpperCase() : any
+>value.toUpperCase : any
+>value : undefined
+>toUpperCase : any
+

tests/cases/conformance/es6/destructuring/destructuringControlFlow.ts

@@ -34,3 +34,9 @@ function f4() {
     ({ ["x"]: x } = 0);  // Error
     ({ ["x" + ""]: x } = 0);  // Errpr
 }
+
+// Repro from #31770
+
+type KeyValue = [string, string?];
+let [key, value]: KeyValue = ["foo"];
+value.toUpperCase();  // Error