[ASDAlexander77]

TypeScript gives a derived class with no constructor an implicit constructor(...args) { super(...args); }. tslang generated one only when the class had field initializers, and as constructor() { super(); }:

class Base {
    constructor(protected a: int, protected b: int = 0) {}
    sum(): int { return this.a + this.b; }
}
class Derived extends Base {
    extra = 1;                    // no constructor
}
new Derived(2, 3);                // error: Expected 1-2 arguments, but got 0. (at 1:1)

• Implicit constructor (mlirGenClassDefaultConstructor): it takes the base constructor's parameters, typed from its function type, so a generic base is already specialized. Optional and rest parameters are included. It passes them to super, and the base applies its own defaults. The parameters are named .argN, so a field initializer, which runs in this constructor, still sees an outer variable of the same name.
• super(a, ...rest) passed an empty rest parameter. The callee of a super call is the base class, so its arguments were generated with no parameter list, and a spread had no count to fill. They are now generated against the base constructor's function type.
• Locations: errors in the generated constructor, and in the assignment generated for a field initializer, were reported at 1:1 because those nodes had no position. They are now reported at the class and at the field. For example, protected argv: Ref<string> = null; now reports at 6:5.

Tests: 00class_implicit_constructor.ts (compile + JIT, and the rc/none corpus) covers defaults, optional and rest parameters, a two-level chain, generic and specialized bases, and the shadowing case. Two diagnostic-location tests check the error positions. I also checked by hand a base imported from another module, with and without the JIT cache. Full suite: 4020/4020 passed (Release).

Found while porting native_ts_graphics samples (issues 1 and 2 of the native_ts_graphics findings; the location part of issue 4). With this, the forwarding constructors added in native_ts_graphics PR #48 can be deleted.

🤖 Generated with Claude Code