[ASDAlexander77]

Stacked on #612: merge that first, then retarget this PR to main.

class W { fn: () => int = () => 7 } cast to interface HasFn { fn: () => int } failed with field type not matching for "fn", although both print as () => s32.

Cause

The class stores the field as !ts.hybrid_func<, si32>, a {function, this or null} pair: a signature type node always becomes a HybridFunctionType. The interface field is !ts.func<!ts.opaque, si32>, a function that takes the object as this. The slot can't hand out a hybrid that way: a null-this hybrid has no this parameter, and a bound one has its own receiver.

Change

• In the field callback of mlirGenClassVirtualTableDefinitionForInterface, a class field of function kind whose signature matches (TestFunctionTypesMatchWithObjectMethods) is accepted.
• A private thunk <Class>.<Iface>..vtbl.<field>.thunk(this, p0..pn) is synthesized that calls this.<field>(p0..pn) (generateSynthMethodToCallField, MLIRGenImpl.h, modelled on generateSynthMethodToCallNewCtor). It handles void returns too.
• The thunk fills the slot through A class method can fill an interface's function-typed field #612's method cell. It reads the field at every call, so a later assignment to the instance's field is seen through the interface.

The limitation from #612 still applies: a write through the interface (h.fn = g) changes the shared cell.

Tests

00interface_function_typed_field_class_field.ts (gc AOT/JIT + rc/none corpus). It covers:

• the task program, an unannotated fn = () => 6 field (stored as a plain function), a capturing closure, and a bound method assigned in the constructor
• a field reassigned after the cast, (int, string) => string, and a void return
• implements, inheritance, and a diamond extends
• one call site shared with an object literal, and the returned bound value

It failed on #612's binary with the original error. Full Release ctest passed (4723/4723). --verify-ownership is clean under rc and none. A signature mismatch still errors, and the message now names the field's type.

Found, not fixed (separate bugs)

• Casting an object literal to the interface drops a closure's context: const o = { fn: cl }; const h: HasFn = o; h.fn() prints garbage.
• class W2 { fn = () => 0; constructor(k: int) { this.fn = () => k; } } crashes on w.fn().
• class W3 { fn = this.m }: w.fn() fails with "not a function to call".

🤖 Generated with Claude Code