Merge pull request #8425 from Microsoft/use-before-def

check usage before declaration for computed properties in destructuri…

Author: vladima

src/compiler/checker.ts

@@ -574,18 +574,28 @@ namespace ts {
             function isImmediatelyUsedInInitializerOfBlockScopedVariable(declaration: VariableDeclaration, usage: Node): boolean {
                 const container = getEnclosingBlockScopeContainer(declaration);
 
-                if (declaration.parent.parent.kind === SyntaxKind.VariableStatement ||
-                    declaration.parent.parent.kind === SyntaxKind.ForStatement) {
-                    // variable statement/for statement case,
-                    // use site should not be inside variable declaration (initializer of declaration or binding element)
-                    return isSameScopeDescendentOf(usage, declaration, container);
-                }
-                else if (declaration.parent.parent.kind === SyntaxKind.ForOfStatement ||
-                    declaration.parent.parent.kind === SyntaxKind.ForInStatement) {
-                    // ForIn/ForOf case - use site should not be used in expression part
-                    const expression = (<ForInStatement | ForOfStatement>declaration.parent.parent).expression;
-                    return isSameScopeDescendentOf(usage, expression, container);
+                switch (declaration.parent.parent.kind) {
+                    case SyntaxKind.VariableStatement:
+                    case SyntaxKind.ForStatement:
+                    case SyntaxKind.ForOfStatement:
+                        // variable statement/for/for-of statement case,
+                        // use site should not be inside variable declaration (initializer of declaration or binding element)
+                        if (isSameScopeDescendentOf(usage, declaration, container)) {
+                            return true;
+                        }
+                        break;
                 }
+
+                switch (declaration.parent.parent.kind) {
+                    case SyntaxKind.ForInStatement:
+                    case SyntaxKind.ForOfStatement:
+                        // ForIn/ForOf case - use site should not be used in expression part
+                        if (isSameScopeDescendentOf(usage, (<ForInStatement | ForOfStatement>declaration.parent.parent).expression, container)) {
+                            return true;
+                        }
+                }
+
+                return false;
             }
 
             function isUsedInFunctionOrNonStaticProperty(declaration: Declaration, usage: Node): boolean {

tests/baselines/reference/blockScopedBindingUsedBeforeDef.errors.txt

@@ -0,0 +1,23 @@
+tests/cases/compiler/blockScopedBindingUsedBeforeDef.ts(2,12): error TS2448: Block-scoped variable 'a' used before its declaration.
+tests/cases/compiler/blockScopedBindingUsedBeforeDef.ts(5,12): error TS2448: Block-scoped variable 'a' used before its declaration.
+tests/cases/compiler/blockScopedBindingUsedBeforeDef.ts(5,35): error TS7027: Unreachable code detected.
+tests/cases/compiler/blockScopedBindingUsedBeforeDef.ts(8,7): error TS2448: Block-scoped variable 'b' used before its declaration.
+
+
+==== tests/cases/compiler/blockScopedBindingUsedBeforeDef.ts (4 errors) ====
+    // 1:
+    for (let {[a]: a} of [{ }]) continue;
+               ~
+!!! error TS2448: Block-scoped variable 'a' used before its declaration.
+    
+    // 2:
+    for (let {[a]: a} = { }; false; ) continue;
+               ~
+!!! error TS2448: Block-scoped variable 'a' used before its declaration.
+                                      ~~~~~~~~
+!!! error TS7027: Unreachable code detected.
+    
+    // 3:
+    let {[b]: b} = { };
+          ~
+!!! error TS2448: Block-scoped variable 'b' used before its declaration.

tests/baselines/reference/blockScopedBindingUsedBeforeDef.js

@@ -0,0 +1,21 @@
+//// [blockScopedBindingUsedBeforeDef.ts]
+// 1:
+for (let {[a]: a} of [{ }]) continue;
+
+// 2:
+for (let {[a]: a} = { }; false; ) continue;
+
+// 3:
+let {[b]: b} = { };
+
+//// [blockScopedBindingUsedBeforeDef.js]
+// 1:
+for (var _i = 0, _a = [{}]; _i < _a.length; _i++) {
+    var _b = a, a = _a[_i][_b];
+    continue;
+}
+// 2:
+for (var _c = a, a = {}[_c]; false;)
+    continue;
+// 3:
+var _d = b, b = {}[_d];

tests/cases/compiler/blockScopedBindingUsedBeforeDef.ts

@@ -0,0 +1,8 @@
+// 1:
+for (let {[a]: a} of [{ }]) continue;
+
+// 2:
+for (let {[a]: a} = { }; false; ) continue;
+
+// 3:
+let {[b]: b} = { };