fix(hir): #832 — class decorator identity-return (return target) accepted as no-op

[proggeramlug]

Summary

• @decorator class X {} where the decorator returns the target class (return target) no longer throws TypeError: ... returned a value. Identity-return is treated as a no-op.
• Genuine class-replacement returns (return SomeOtherClass) still throw with the same actionable message, preserving the safety guarantee from PR Add legacy TypeScript decorator metadata support #754.
• Fixes decorator that returns the target class is rejected; Node accepts it #832.

Root cause

append_decorator_invocations_inner in crates/perry-hir/src/lower.rs emitted if (__ret !== undefined) throw TypeError(...) — strict on any non-undefined return. Real-world decorators (TypeORM @Entity, NestJS, GraphQL wrappers, decorator-factory output not simplified for production) routinely end with return target / return descriptor as a no-op, and the trivial identity decorator from the bug report was rejected too.

Fix

Augment the condition to also accept identity returns:

if (__perry_dec_ret !== undefined && __perry_dec_ret !== target) {
  throw TypeError(...);
}

target comes from invocation_args.first() — the Expr::ClassRef(class.name) that append_class_decorator_invocations passes as the decorator's first argument. So the runtime comparison is between the decorator's return value and the original class reference it received. Falls back to the strict-undefined check if invocation_args is empty (defensive).

Test plan

• Issue repro now prints Hello, world — @logged (returns target) lets the class instantiate and the method dispatch correctly.
• Regression: @replaceClass (returns a different function) still throws the TypeError. The Add legacy TypeScript decorator metadata support #754 silent-class-replacement safety guarantee is preserved.
• Gap suite 34/36 — same as before (the two failures are test_gap_console_methods and test_gap_regexp_advanced / String.prototype.replace(/.../g, fn) — replacer-fn return value is dropped (replaces with empty string) #833, both unrelated).

Closes #832. Refs #793, #801, #754.