-aot defines a struct before the struct it holds by value when the inner struct points back at it, so the generated C++ does not compile (field has incomplete type)

[lookibed]

daslang 0.6.4 at master 237df6024, Linux x86_64 (WSL2, kernel 6.6), gcc 11.4, Release.

When a struct holds another struct by value and that inner struct points back at the outer one, -aot emits the outer struct's definition before the inner one's. C++ needs a complete type for a by-value member, so the generated file does not compile. The interpreter runs the same program; the -jit and -aot tiers disagree with it only because the C++ never builds.

Reproduction

back_pointer.das:

options gen2

struct Outer {
    next : Outer?
    embedded : Inner
    tag : int
}

struct Inner {
    owner : Outer?
    a : int
    b : int
}

[export]
def main() {
    var o = Outer(tag = 7, embedded = Inner(a = 1, b = 2))
    o.embedded.owner = unsafe(addr(o))
    print("{o.embedded.owner.tag} {o.embedded.a + o.embedded.b}\n")
}

$ daslang back_pointer.das
7 3
$ daslang -aot back_pointer.das back_pointer.das.cpp
$ g++ -std=c++17 -fsyntax-only -I include back_pointer.das.cpp
back_pointer.das.cpp:345:18: error: field 'embedded' has incomplete type 'das::_anon_...::Inner'
back_pointer.das.cpp:348:28: error: static assertion failed: structure size mismatch with DAS
back_pointer.das.cpp:351:34: error: static assertion failed: structure field offset mismatch with DAS

The generated file, in order:

struct Outer {
    struct Outer * next;
    struct Inner embedded;     // Inner is not defined yet
    int32_t tag;
};
...
struct Inner {
    struct Outer * owner;
    ...

Declaring Inner before Outer in the source is a workaround; a pointer member (owner : Outer?) needs only a forward declaration, which the emitter already writes for every struct.

Expected

The emitter orders struct definitions by their by-value dependencies (a struct is defined after every struct it embeds), and treats pointer members as satisfied by the forward declaration. The program compiles under -aot as it runs in the interpreter.

Test

Drops into tests/language/ as test_struct_by_value_back_pointer.das: it passes interpreted, and the AOT lane (test_aot_subset compiles tests/language) fails to build the generated C++ on master.

options gen2
require dastest/testing_boost

struct Outer {
    next : Outer?
    embedded : Inner
    tag : int
}

struct Inner {
    owner : Outer?
    a : int
    b : int
}

[test]
def test_by_value_member_with_a_back_pointer(t : T?) {
    var o = Outer(tag = 7, embedded = Inner(a = 1, b = 2))
    o.embedded.owner = unsafe(addr(o))
    t |> equal(o.embedded.owner.tag, 7)
    t |> equal(o.embedded.a + o.embedded.b, 3)
}