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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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5
Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
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@ -489,16 +489,17 @@ Bytecode::CodeGenerationErrorOr<Optional<Bytecode::Operand>> AssignmentExpressio
generator.emit_set_variable(identifier, rval);
} else if (is<MemberExpression>(*lhs)) {
auto& expression = static_cast<MemberExpression const&>(*lhs);
auto base_identifier = generator.intern_identifier_for_expression(expression.object());
if (expression.is_computed()) {
if (!lhs_is_super_expression)
generator.emit<Bytecode::Op::PutByValue>(*base, *computed_property, rval);
generator.emit<Bytecode::Op::PutByValue>(*base, *computed_property, rval, Bytecode::Op::PropertyKind::KeyValue, move(base_identifier));
else
generator.emit<Bytecode::Op::PutByValueWithThis>(*base, *computed_property, *this_value, rval);
} else if (expression.property().is_identifier()) {
auto identifier_table_ref = generator.intern_identifier(verify_cast<Identifier>(expression.property()).string());
if (!lhs_is_super_expression)
generator.emit<Bytecode::Op::PutById>(*base, identifier_table_ref, rval, Bytecode::Op::PropertyKind::KeyValue, generator.next_property_lookup_cache());
generator.emit<Bytecode::Op::PutById>(*base, identifier_table_ref, rval, Bytecode::Op::PropertyKind::KeyValue, generator.next_property_lookup_cache(), move(base_identifier));
else
generator.emit<Bytecode::Op::PutByIdWithThis>(*base, *this_value, identifier_table_ref, rval, Bytecode::Op::PropertyKind::KeyValue, generator.next_property_lookup_cache());
} else if (expression.property().is_private_identifier()) {