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LibJS/Bytecode: Check for lexical bindings only in current scope

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BlockDeclarationInstantiation takes as input the new lexical
environment that was created and checks if there is a binding for the
current name only in this new scope.

This allows shadowing lexical variables and prevents us crashing due to
an already initialized lexical variable in this case:
```js
let x = 1;
{
    let x = 1;
}
```
This commit is contained in:
Luke Wilde 2022-07-17 19:09:19 +01:00 • committed by Linus Groh
parent c55a4c7f30
commit 3a48c7fdaf
2 changed files with 11 additions and 2 deletions
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4
Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
View file

@ -45,7 +45,9 @@ Bytecode::CodeGenerationErrorOr<void> ScopeNode::generate_bytecode(Bytecode::Gen
auto is_constant_declaration = declaration.is_constant_declaration();
declaration.for_each_bound_name([&](auto const& name) {
auto index = generator.intern_identifier(name);
if (is_constant_declaration || !generator.has_binding(index)) {
// NOTE: BlockDeclarationInstantiation takes as input the new lexical environment that was created and checks if there is a binding for the current name only in this new scope.
// For example: `{ let a = 1; { let a = 2; } }`. The second `a` will shadow the first `a` instead of re-initializing or setting it.
if (is_constant_declaration || !generator.has_binding_in_current_scope(index)) {
generator.register_binding(index);
generator.emit<Bytecode::Op::CreateVariable>(index, Bytecode::Op::EnvironmentMode::Lexical, is_constant_declaration);
}

9
Userland/Libraries/LibJS/Bytecode/Generator.h
View file

@ -138,7 +138,7 @@ public:
{
m_variable_scopes.last_matching([&](auto& x) { return x.mode == BindingMode::Global || x.mode == mode; })->known_bindings.set(identifier);
}
bool has_binding(IdentifierTableIndex identifier, Optional<BindingMode> const& specific_binding_mode = {})
bool has_binding(IdentifierTableIndex identifier, Optional<BindingMode> const& specific_binding_mode = {}) const
{
for (auto index = m_variable_scopes.size(); index > 0; --index) {
auto& scope = m_variable_scopes[index - 1];
@ -151,6 +151,13 @@ public:
}
return false;
}
bool has_binding_in_current_scope(IdentifierTableIndex identifier) const
{
if (m_variable_scopes.is_empty())
return false;
return m_variable_scopes.last().known_bindings.contains(identifier);
}
void begin_variable_scope(BindingMode mode = BindingMode::Lexical, SurroundingScopeKind kind = SurroundingScopeKind::Block);
void end_variable_scope();