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LibJS: Replace the custom unwind mechanism with completions :^)

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This includes:

- Parsing proper LabelledStatements with try_parse_labelled_statement()
- Removing LabelableStatement
- Implementing the LoopEvaluation semantics via loop_evaluation() in
  each IterationStatement subclass; and IterationStatement evaluation
  via {For,ForIn,ForOf,ForAwaitOf,While,DoWhile}Statement::execute()
- Updating ReturnStatement, BreakStatement and ContinueStatement to
  return the appropriate completion types
- Basically reimplementing TryStatement and SwitchStatement according to
  the spec, using completions
- Honoring result completion types in AsyncBlockStart and
  OrdinaryCallEvaluateBody
- Removing any uses of the VM unwind mechanism - most importantly,
  VM::throw_exception() now exclusively sets an exception and no longer
  triggers any unwinding mechanism.
  However, we already did a good job updating all of LibWeb and userland
  applications to not use it, and the few remaining uses elsewhere don't
  rely on unwinding AFAICT.
This commit is contained in:
Linus Groh 2022-01-05 19:11:16 +01:00
parent eed764e1dd
commit 9d0d3affd4
16 changed files with 512 additions and 279 deletions
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25
Userland/Libraries/LibJS/Parser.cpp
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@ -822,7 +822,7 @@ RefPtr<FunctionExpression> Parser::try_parse_arrow_function_expression(bool expe
/* might_need_arguments_object */ false, contains_direct_call_to_eval, /* is_arrow_function */ true);
}
RefPtr<Statement> Parser::try_parse_labelled_statement(AllowLabelledFunction allow_function)
RefPtr<LabelledStatement> Parser::try_parse_labelled_statement(AllowLabelledFunction allow_function)
{
{
// NOTE: This is a fast path where we try to fail early to avoid the expensive save_state+load_state.
@ -873,7 +873,7 @@ RefPtr<Statement> Parser::try_parse_labelled_statement(AllowLabelledFunction all
if (m_state.labels_in_scope.contains(identifier))
syntax_error(String::formatted("Label '{}' has already been declared", identifier));
RefPtr<Statement> labelled_statement;
RefPtr<Statement> labelled_item;
auto is_iteration_statement = false;
@ -887,16 +887,16 @@ RefPtr<Statement> Parser::try_parse_labelled_statement(AllowLabelledFunction all
if (function_declaration->kind() == FunctionKind::Async)
syntax_error("Async functions cannot be defined in labelled statements");
labelled_statement = move(function_declaration);
labelled_item = move(function_declaration);
} else {
m_state.labels_in_scope.set(identifier, {});
labelled_statement = parse_statement(allow_function);
if (is<IterationStatement>(*labelled_statement)) {
labelled_item = parse_statement(allow_function);
// Extract the innermost statement from a potentially nested chain of LabelledStatements.
auto statement = labelled_item;
while (is<LabelledStatement>(*statement))
statement = static_cast<LabelledStatement&>(*statement).labelled_item();
if (is<IterationStatement>(*statement))
is_iteration_statement = true;
static_cast<IterationStatement&>(*labelled_statement).add_label(identifier);
} else if (is<LabelableStatement>(*labelled_statement)) {
static_cast<LabelableStatement&>(*labelled_statement).add_label(identifier);
}
}
if (!is_iteration_statement) {
@ -906,7 +906,7 @@ RefPtr<Statement> Parser::try_parse_labelled_statement(AllowLabelledFunction all
m_state.labels_in_scope.remove(identifier);
return labelled_statement.release_nonnull();
return create_ast_node<LabelledStatement>({ m_state.current_token.filename(), rule_start.position(), position() }, identifier, labelled_item.release_nonnull());
}
RefPtr<MetaProperty> Parser::try_parse_new_target_expression()
@ -1286,7 +1286,10 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
auto super_call = create_ast_node<SuperCall>(
{ m_state.current_token.filename(), rule_start.position(), position() },
Vector { CallExpression::Argument { create_ast_node<Identifier>({ m_state.current_token.filename(), rule_start.position(), position() }, "args"), true } });
constructor_body->append(create_ast_node<ExpressionStatement>({ m_state.current_token.filename(), rule_start.position(), position() }, move(super_call)));
// NOTE: While the JS approximation above doesn't do `return super(...args)`, the
// abstract closure is expected to capture and return the result, so we do need a
// return statement here to create the correct completion.
constructor_body->append(create_ast_node<ReturnStatement>({ m_state.current_token.filename(), rule_start.position(), position() }, move(super_call)));
constructor = create_ast_node<FunctionExpression>(
{ m_state.current_token.filename(), rule_start.position(), position() }, class_name, move(constructor_body),