Merge pull request microsoft#7555 from Microsoft/destructuring-variable-declarations

Destructuring in variable declarations when module kind is not ES6

Author: vladima

src/compiler/emitter.ts

@@ -4218,12 +4218,31 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
 
  function emitVariableDeclaration(node: VariableDeclaration) {
  if (isBindingPattern(node.name)) {
- if (languageVersion < ScriptTarget.ES6) {
- emitDestructuring(node, /*isAssignmentExpressionStatement*/ false);
- }
- else {
+ const isExported = getCombinedNodeFlags(node) & NodeFlags.Export;
+ if (languageVersion >= ScriptTarget.ES6 && (!isExported || modulekind === ModuleKind.ES6)) {
+ // emit ES6 destructuring only if target module is ES6 or variable is not exported
+ // exported variables in CJS/AMD are prefixed with 'exports.' so result javascript { exports.toString } = 1; is illegal
+
+ const isTopLevelDeclarationInSystemModule =
+ modulekind === ModuleKind.System &&
+ shouldHoistVariable(node, /*checkIfSourceFileLevelDecl*/true);
+
+ if (isTopLevelDeclarationInSystemModule) {
+ // In System modules top level variables are hoisted
+ // so variable declarations with destructuring are turned into destructuring assignments.
+ // As a result, they will need parentheses to disambiguate object binding assignments from blocks.
+ write("(");
+ }
+
  emit(node.name);
  emitOptional(" = ", node.initializer);
+
+ if (isTopLevelDeclarationInSystemModule) {
+ write(")");
+ }
+ }
+ else {
+ emitDestructuring(node, /*isAssignmentExpressionStatement*/ false);
  }
  }
  else {

tests/baselines/reference/destructuringInVariableDeclarations1.js

@@ -0,0 +1,13 @@
+//// [destructuringInVariableDeclarations1.ts]
+export let { toString } = 1;
+{
+ let { toFixed } = 1;
+}
+
+
+//// [destructuringInVariableDeclarations1.js]
+"use strict";
+exports.toString = (1).toString;
+{
+ let { toFixed } = 1;
+}

tests/baselines/reference/destructuringInVariableDeclarations1.symbols

@@ -0,0 +1,8 @@
+=== tests/cases/compiler/destructuringInVariableDeclarations1.ts ===
+export let { toString } = 1;
+>toString : Symbol(toString, Decl(destructuringInVariableDeclarations1.ts, 0, 12))
+{
+ let { toFixed } = 1;
+>toFixed : Symbol(toFixed, Decl(destructuringInVariableDeclarations1.ts, 2, 9))
+}
+

tests/baselines/reference/destructuringInVariableDeclarations1.types

@@ -0,0 +1,10 @@
+=== tests/cases/compiler/destructuringInVariableDeclarations1.ts ===
+export let { toString } = 1;
+>toString : (radix?: number) => string
+>1 : number
+{
+ let { toFixed } = 1;
+>toFixed : (fractionDigits?: number) => string
+>1 : number
+}
+

tests/baselines/reference/destructuringInVariableDeclarations2.js

@@ -0,0 +1,14 @@
+//// [destructuringInVariableDeclarations2.ts]
+let { toString } = 1;
+{
+ let { toFixed } = 1;
+}
+export {};
+
+
+//// [destructuringInVariableDeclarations2.js]
+"use strict";
+let { toString } = 1;
+{
+ let { toFixed } = 1;
+}

tests/baselines/reference/destructuringInVariableDeclarations2.symbols

@@ -0,0 +1,9 @@
+=== tests/cases/compiler/destructuringInVariableDeclarations2.ts ===
+let { toString } = 1;
+>toString : Symbol(toString, Decl(destructuringInVariableDeclarations2.ts, 0, 5))
+{
+ let { toFixed } = 1;
+>toFixed : Symbol(toFixed, Decl(destructuringInVariableDeclarations2.ts, 2, 9))
+}
+export {};
+

tests/baselines/reference/destructuringInVariableDeclarations2.types

@@ -0,0 +1,11 @@
+=== tests/cases/compiler/destructuringInVariableDeclarations2.ts ===
+let { toString } = 1;
+>toString : (radix?: number) => string
+>1 : number
+{
+ let { toFixed } = 1;
+>toFixed : (fractionDigits?: number) => string
+>1 : number
+}
+export {};
+

tests/baselines/reference/destructuringInVariableDeclarations3.js

@@ -0,0 +1,15 @@
+//// [destructuringInVariableDeclarations3.ts]
+export let { toString } = 1;
+{
+ let { toFixed } = 1;
+}
+
+
+//// [destructuringInVariableDeclarations3.js]
+define(["require", "exports"], function (require, exports) {
+ "use strict";
+ exports.toString = (1).toString;
+ {
+ let { toFixed } = 1;
+ }
+});

tests/baselines/reference/destructuringInVariableDeclarations3.symbols

@@ -0,0 +1,8 @@
+=== tests/cases/compiler/destructuringInVariableDeclarations3.ts ===
+export let { toString } = 1;
+>toString : Symbol(toString, Decl(destructuringInVariableDeclarations3.ts, 0, 12))
+{
+ let { toFixed } = 1;
+>toFixed : Symbol(toFixed, Decl(destructuringInVariableDeclarations3.ts, 2, 9))
+}
+

tests/baselines/reference/destructuringInVariableDeclarations3.types

@@ -0,0 +1,10 @@
+=== tests/cases/compiler/destructuringInVariableDeclarations3.ts ===
+export let { toString } = 1;
+>toString : (radix?: number) => string
+>1 : number
+{
+ let { toFixed } = 1;
+>toFixed : (fractionDigits?: number) => string
+>1 : number
+}
+