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Fix using transform variable shadowing in for-of loops #61934

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234 changes: 122 additions & 112 deletions src/compiler/transformers/esnext.ts
Original file line number Diff line number Diff line change
@@ -1,67 +1,67 @@
import {
addEmitHelpers,
addRange,
append,
arrayFrom,
BindingElement,
Block,
Bundle,
CaseOrDefaultClause,
chainBundle,
ClassDeclaration,
Debug,
EmitFlags,
ExportAssignment,
ExportSpecifier,
Expression,
firstOrUndefined,
ForOfStatement,
ForStatement,
GeneratedIdentifierFlags,
getEmitFlags,
hasSyntacticModifier,
Identifier,
IdentifierNameMap,
isArray,
isBindingPattern,
isBlock,
isCaseClause,
isCustomPrologue,
isExpression,
isGeneratedIdentifier,
isIdentifier,
isLocalName,
isNamedEvaluation,
isOmittedExpression,
isPrologueDirective,
isSourceFile,
isStatement,
isVariableDeclarationList,
isVariableStatement,
ModifierFlags,
Node,
NodeFlags,
setCommentRange,
setEmitFlags,
setOriginalNode,
setSourceMapRange,
setTextRange,
skipOuterExpressions,
SourceFile,
Statement,
SwitchStatement,
SyntaxKind,
TransformationContext,
TransformFlags,
transformNamedEvaluation,
VariableDeclaration,
VariableDeclarationList,
VariableStatement,
visitArray,
visitEachChild,
visitNode,
visitNodes,
VisitResult,
import {
addEmitHelpers,
addRange,
append,
arrayFrom,
BindingElement,
Block,
Bundle,
CaseOrDefaultClause,
chainBundle,
ClassDeclaration,
Debug,
EmitFlags,
ExportAssignment,
ExportSpecifier,
Expression,
firstOrUndefined,
ForOfStatement,
ForStatement,
GeneratedIdentifierFlags,
getEmitFlags,
hasSyntacticModifier,
Identifier,
IdentifierNameMap,
isArray,
isBindingPattern,
isBlock,
isCaseClause,
isCustomPrologue,
isExpression,
isGeneratedIdentifier,
isIdentifier,
isLocalName,
isNamedEvaluation,
isOmittedExpression,
isPrologueDirective,
isSourceFile,
isStatement,
isVariableDeclarationList,
isVariableStatement,
ModifierFlags,
Node,
NodeFlags,
setCommentRange,
setEmitFlags,
setOriginalNode,
setSourceMapRange,
setTextRange,
skipOuterExpressions,
SourceFile,
Statement,
SwitchStatement,
SyntaxKind,
TransformationContext,
TransformFlags,
transformNamedEvaluation,
VariableDeclaration,
VariableDeclarationList,
VariableStatement,
visitArray,
visitEachChild,
visitNode,
visitNodes,
VisitResult,
} from "../_namespaces/ts.js";

const enum UsingKind {
Expand Down Expand Up @@ -289,54 +289,64 @@ export function transformESNext(context: TransformationContext): (x: SourceFile
);
}

return visitEachChild(node, visitor, context);
}

function visitForOfStatement(node: ForOfStatement) {
if (isUsingVariableDeclarationList(node.initializer)) {
// given:
//
// for (using x of y) { ... }
//
// produces a shallow transformation to:
//
// for (const x_1 of y) {
// using x = x;
// ...
// }
//
// before handing the shallow transformation back to the visitor for an in-depth transformation.
const forInitializer = node.initializer;
const forDecl = firstOrUndefined(forInitializer.declarations) || factory.createVariableDeclaration(factory.createTempVariable(/*recordTempVariable*/ undefined));

const isAwaitUsing = getUsingKindOfVariableDeclarationList(forInitializer) === UsingKind.Async;
const temp = factory.getGeneratedNameForNode(forDecl.name);
const usingVar = factory.updateVariableDeclaration(forDecl, forDecl.name, /*exclamationToken*/ undefined, /*type*/ undefined, temp);
const usingVarList = factory.createVariableDeclarationList([usingVar], isAwaitUsing ? NodeFlags.AwaitUsing : NodeFlags.Using);
const usingVarStatement = factory.createVariableStatement(/*modifiers*/ undefined, usingVarList);
return visitNode(
factory.updateForOfStatement(
node,
node.awaitModifier,
factory.createVariableDeclarationList([
factory.createVariableDeclaration(temp),
], NodeFlags.Const),
node.expression,
isBlock(node.statement) ?
factory.updateBlock(node.statement, [
usingVarStatement,
...node.statement.statements,
]) :
factory.createBlock([
usingVarStatement,
node.statement,
], /*multiLine*/ true),
),
visitor,
isStatement,
);
}
return visitEachChild(node, visitor, context);
return visitEachChild(node, visitor, context);
}

function visitForOfStatement(node: ForOfStatement) {
if (isUsingVariableDeclarationList(node.initializer)) {
// given:
//
// for (using x of y) { ... }
//
// produces a shallow transformation to:
//
// for (const x_1 of y) {
// using x = x_1;
// { ... }
// }
//
// where the original loop body is wrapped in an additional block scope
// to handle shadowing variables naturally through block scoping.
const forInitializer = node.initializer;
const forDecl = firstOrUndefined(forInitializer.declarations) || factory.createVariableDeclaration(factory.createTempVariable(/*recordTempVariable*/ undefined));

const isAwaitUsing = getUsingKindOfVariableDeclarationList(forInitializer) === UsingKind.Async;
const temp = factory.getGeneratedNameForNode(forDecl.name);
const usingVar = factory.updateVariableDeclaration(forDecl, forDecl.name, /*exclamationToken*/ undefined, /*type*/ undefined, temp);
const usingVarList = factory.createVariableDeclarationList([usingVar], isAwaitUsing ? NodeFlags.AwaitUsing : NodeFlags.Using);
const usingVarStatement = factory.createVariableStatement(/*modifiers*/ undefined, usingVarList);

// Wrap the original loop body in an additional block scope to handle shadowing
// Don't create an extra block if the original statement is empty or contains only empty statements
const isEmptyBlock = isBlock(node.statement) && (
node.statement.statements.length === 0 ||
node.statement.statements.every(stmt => stmt.kind === SyntaxKind.EmptyStatement)
);
const shouldWrapInBlock = !isEmptyBlock;

const statements: Statement[] = [usingVarStatement];
if (shouldWrapInBlock) {
const wrappedStatement = isBlock(node.statement) ?
node.statement :
factory.createBlock([node.statement], /*multiLine*/ true);
statements.push(wrappedStatement);
}

return visitNode(
factory.updateForOfStatement(
node,
node.awaitModifier,
factory.createVariableDeclarationList([
factory.createVariableDeclaration(temp),
], NodeFlags.Const),
node.expression,
factory.createBlock(statements, /*multiLine*/ true),
),
visitor,
isStatement,
);
}
return visitEachChild(node, visitor, context);
}

function visitCaseOrDefaultClause(node: CaseOrDefaultClause, envBinding: Identifier) {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -118,7 +118,9 @@ try {
var env_1 = { stack: [], error: void 0, hasError: false };
try {
var _e = __addDisposableResource(env_1, _e_1, true);
;
{
;
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We should consider a block with just an empty statement the same as an empty block and avoid emitting the new block.

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Fixed in commit 957cf79. The implementation now considers blocks containing only empty statements as effectively empty and avoids generating the extra wrapping block in those cases.

}
}
catch (e_2) {
env_1.error = e_2;
Expand Down Expand Up @@ -159,7 +161,9 @@ export function test() {
case 3:
_f.trys.push([3, 4, 5, 8]);
_b = __addDisposableResource(env_2, _b_1, true);
;
{
;
}
return [3 /*break*/, 8];
case 4:
e_3 = _f.sent();
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -107,7 +107,9 @@ for (var _i = 0, x_1 = x; _i < x_1.length; _i++) {
var env_1 = { stack: [], error: void 0, hasError: false };
try {
var _a = __addDisposableResource(env_1, _a_1, true);
;
{
;
}
}
catch (e_1) {
env_1.error = e_1;
Expand Down Expand Up @@ -135,7 +137,9 @@ export function test() {
case 2:
_b.trys.push([2, 3, 4, 7]);
_a = __addDisposableResource(env_2, _a_2, true);
;
{
;
}
return [3 /*break*/, 7];
case 3:
e_2 = _b.sent();
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
main.ts(12,7): error TS2481: Cannot initialize outer scoped variable 'baz' in the same scope as block scoped declaration 'baz'.


==== main.ts (1 errors) ====
class Foo {}

for (using foo of []) {
const foo = new Foo();
}

for (using bar of []) {
let bar = "test";
}

for (using baz of []) {
var baz = 42;
~~~
!!! error TS2481: Cannot initialize outer scoped variable 'baz' in the same scope as block scoped declaration 'baz'.
}

==== tslib.d.ts (0 errors) ====
export declare function __addDisposableResource<T>(env: any, value: T, async: boolean): T;
export declare function __disposeResources(env: any): void;

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