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LibJS/Bytecode: Handle awkward initialization case for duplicate var

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`var` declarations can have duplicates, but duplicate `let` or `const`
bindings are a syntax error.

Because of this, we can sink `let` and `const` directly into the
preferred_dst if available. This is not safe for `var` since the
preferred_dst may be used in the initializer.

This patch fixes the issue by simply skipping the preferred_dst
optimization for `var` declarations.
This commit is contained in:
Andreas Kling 2024-03-01 12:54:50 +01:00
parent 2bbdfe0fba
commit bc21ed151e
Notes: sideshowbarker 2024-07-17 01:06:10 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/bc21ed151e
Pull-request: https://github.com/SerenityOS/serenity/pull/23413
2 changed files with 23 additions and 3 deletions
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11
Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
View File

@ -1452,10 +1452,15 @@ Bytecode::CodeGenerationErrorOr<Optional<Bytecode::Operand>> VariableDeclaration
Bytecode::Generator::SourceLocationScope scope(generator, *this);
for (auto& declarator : m_declarations) {
// NOTE: `var` declarations can have duplicates, but duplicate `let` or `const` bindings are a syntax error.
// Because of this, we can sink `let` and `const` directly into the preferred_dst if available.
// This is not safe for `var` since the preferred_dst may be used in the initializer.
Optional<Bytecode::Operand> init_dst;
if (auto const* identifier = declarator->target().get_pointer<NonnullRefPtr<Identifier const>>()) {
if ((*identifier)->is_local()) {
init_dst = Bytecode::Operand(Bytecode::Operand::Type::Local, (*identifier)->local_variable_index());
if (declaration_kind() != DeclarationKind::Var) {
if (auto const* identifier = declarator->target().get_pointer<NonnullRefPtr<Identifier const>>()) {
if ((*identifier)->is_local()) {
init_dst = Bytecode::Operand(Bytecode::Operand::Type::Local, (*identifier)->local_variable_index());
}
}
}

15
Userland/Libraries/LibJS/Tests/var-scoping.js
View File

@ -33,3 +33,18 @@ test("Issue #8198 arrow function escapes function scope", () => {
f();
expect(b).toBe(3);
});
test("Referencing the declared var in the initializer of a duplicate var declaration", () => {
function c(e) {
e.foo;
}
function h() {}
function go() {
var p = true;
var p = h() || c(p);
return 0;
}
// It's all good as long as go() doesn't throw.
expect(go()).toBe(0);
});