Each fix is pinned by a regression test in src/regressions.test.ts describing the
old behaviour.
- Inheritance dropped base-class rules. A subclass re-decorating an inherited
property registered its constraints against its own prototype, and validate()
read only the nearest set, so everything the base declared was silently lost.
Constraints are now merged down the whole prototype chain, base first, with
genuinely identical rules collapsed so restating @IsString() on an override
does not double-report. The library's own example.ts was affected: Media's
@IsString() title had never been enforced for Book.
- Circular references exhausted the heap. serialize() recursed forever, taking
8 GB and the process with it; it now tracks ancestors and raises a
JsonMappingError naming the cause. Diamonds still serialize. validate() skips
back-edges instead of recursing.
- @Matches with a g or y flag was stateful: RegExp.test advances lastIndex, so
validating the same value twice gave different answers. Those flags are
stripped.
- An unmatched @JsonPolymorphic discriminator silently dropped the value — the
single-object branch fell through without assigning. The raw value is now
preserved, with { onUnknown: 'error' } and { fallback } to choose otherwise.
- Custom @JsonSerialize serializers ran on null/undefined, crashing on any unset
optional property. They now only see real values.
- serialize() read obj.constructor.prototype, which throws for null-prototype
objects; both engines now agree on Object.getPrototypeOf.
- __proto__, constructor and prototype arriving in untrusted JSON were copied
onto the instance, detaching it from its own class. They are dropped.
- The "each element in ..." prefix was glued onto caller-supplied messages, and
two rules sharing a name overwrote each other so only one failure surfaced.
Also adds toInstanceArray/fromJsonArray, since toInstance and fromJson accept
arrays at runtime but type the result as T, and reports a non-JSON request body
in fromRequest as a JsonMappingError rather than a raw SyntaxError.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SAcqrz3FcadkYr3xG32CjK
