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LibJS: Include identifier information in nullish property write access

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When a PutById / PutByValue bytecode operation results in accessing a
nullish object, we now include the name of the property and the object
being accessed in the exception message (if available). This should make
it easier to debug live websites.

For example, the following errors would all previously produce a generic
error message of "ToObject on null or undefined":

  > foo = null
  > foo.bar = 1
  Uncaught exception:
  [TypeError] Cannot access property "bar" on null object "foo"
      at <unknown>

  > foo = { bar: undefined }
  > foo.bar.baz = 1
  Uncaught exception:
  [TypeError] Cannot access property "baz" on undefined object "foo.bar"
      at <unknown>

Note we certainly don't capture all possible nullish property write
accesses here. This just covers cases I've seen most on live websites;
we can cover more cases as they arise.
This commit is contained in:
Timothy Flynn 2024-03-29 12:10:52 -04:00 • committed by Andreas Kling
commit 22fdcfbc50
Notes: sideshowbarker 2024-07-17 08:55:54 +09:00
5 changed files with 42 additions and 12 deletions
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12
Userland/Libraries/LibJS/Bytecode/CommonImplementations.h
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@ -248,14 +248,18 @@ inline ThrowCompletionOr<Value> get_global(Bytecode::Interpreter& interpreter, D
return vm.throw_completion<ReferenceError>(ErrorType::UnknownIdentifier, identifier);
}
inline ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value, Value value, PropertyKey name, Op::PropertyKind kind, PropertyLookupCache* cache = nullptr)
inline ThrowCompletionOr<void> put_by_property_key(VM& vm, Value base, Value this_value, Value value, Optional<DeprecatedFlyString const&> const& base_identifier, PropertyKey name, Op::PropertyKind kind, PropertyLookupCache* cache = nullptr)
{
// Better error message than to_object would give
if (vm.in_strict_mode() && base.is_nullish())
return vm.throw_completion<TypeError>(ErrorType::ReferenceNullishSetProperty, name, base.to_string_without_side_effects());
// a. Let baseObj be ? ToObject(V.[[Base]]).
auto object = TRY(base.to_object(vm));
auto maybe_object = base.to_object(vm);
if (maybe_object.is_error())
return throw_null_or_undefined_property_access(vm, base, base_identifier, name);
auto object = maybe_object.release_value();
if (kind == Op::PropertyKind::Getter || kind == Op::PropertyKind::Setter) {
// The generator should only pass us functions for getters and setters.
VERIFY(value.is_function());
@ -411,7 +415,7 @@ inline Value new_function(VM& vm, FunctionExpression const& function_node, Optio
return value;
}
inline ThrowCompletionOr<void> put_by_value(VM& vm, Value base, Value property_key_value, Value value, Op::PropertyKind kind)
inline ThrowCompletionOr<void> put_by_value(VM& vm, Value base, Optional<DeprecatedFlyString const&> const& base_identifier, Value property_key_value, Value value, Op::PropertyKind kind)
{
// OPTIMIZATION: Fast path for simple Int32 indexes in array-like objects.
if ((kind == Op::PropertyKind::KeyValue || kind == Op::PropertyKind::DirectKeyValue)
@ -489,7 +493,7 @@ inline ThrowCompletionOr<void> put_by_value(VM& vm, Value base, Value property_k
}
auto property_key = kind != Op::PropertyKind::Spread ? TRY(property_key_value.to_property_key(vm)) : PropertyKey {};
TRY(put_by_property_key(vm, base, base, value, property_key, kind));
TRY(put_by_property_key(vm, base, base, value, base_identifier, property_key, kind));
return {};
}