[BUG]: Modifying nested element of owned DynamicVector crashes during parsing

[isuckatcs]

Bug description

The following snippet crashes during parsing/sema.

from collections.vector import DynamicVector


@value
@register_passable
struct Nested:
    var x: Int


@value
@register_passable
struct Wrapper(CollectionElement):
    var n: Nested


fn foo(owned v: DynamicVector[Wrapper]):
    v[0].n.x = 0

mojo: /__w/modular/modular/KGEN/lib/MojoParser/ExprEmitter.cpp:769: M::KGEN::LIT::SRValue M::KGEN::LIT::ExprEmitter::emitSRValue(ASTExprAnd<M::KGEN::LIT::AnyValue>, M::KGEN::LIT::ExprContext, M::KGEN::LIT::ASTType): Assertion `pValue && "must be PValue if register-passable and not SRValue"' failed.
Please submit a bug report to https://github.com/modularml/mojo/issues and include the crash backtrace along with all the relevant source codes.
Stack dump:
0.      Program arguments: mojo repro.mojo
1.      Crash resolving decl body at loc(".../repro.mojo":16:1)
    >> fn foo(owned v: DynamicVector[Wrapper]):
       ^.......................................
    >>     v[0].n.x = 0
       ................<
2.      Crash parsing statement at loc(".../repro.mojo":17:5)
    >>     v[0].n.x = 0
           ^...........<

Steps to reproduce

• run the snippet in the description with mojo

System information

- Ubuntu 22.04.3 LTS (WSL 2)
- mojo 0.6.1 (876ded2e)
- modular 0.3.1 (589ce200)

[duckki]

I think @value and @register_passable are not compatible each other, since @register_passable requires different style of constructors than what @value would added.

A workaround might be using @register_passable("trivial").

(Indeed, the crash persists even with @register_passable("trivial"). Please disregard my suggestion.)

[isuckatcs]

So, while playing around with @register_passable, I discovered #1579.

I modified the snippet such that the required constructors are specified manually, the way @register_passable requires them to be (based on the compiler error messages), and v[0].n.x = 0 still causes a crash.

@register_passable
struct Nested:
    var x: Int

    fn __init__() -> Nested:
        return Self {x: 0}

    fn __copyinit__(other: Self) -> Nested:
        return Self {x: other.x}


@register_passable
struct Wrapper(CollectionElement):
    var n: Nested

    fn __init__() -> Wrapper:
        return Self {n: Nested()}

    fn __copyinit__(other: Self) -> Wrapper:
        return Self {n: other.n}


fn foo(owned v: DynamicVector[Wrapper]):
    v[0].n.x = 0

mojo: /__w/modular/modular/KGEN/lib/MojoParser/ExprEmitter.cpp:769: M::KGEN::LIT::SRValue M::KGEN::LIT::ExprEmitter::emitSRValue(ASTExprAnd<M::KGEN::LIT::AnyValue>, M::KGEN::LIT::ExprContext, M::KGEN::LIT::ASTType): Assertion `pValue && "must be PValue if register-passable and not SRValue"' failed.

Adding @register_passable("trivial") still results in the same crash regardless of whether @value is present or not.

@register_passable("trivial")
struct Nested:
    var x: Int


@register_passable("trivial")
struct Wrapper(CollectionElement):
    var n: Nested


fn foo(owned v: DynamicVector[Wrapper]):
    v[0].n.x = 0

mojo: /__w/modular/modular/KGEN/lib/MojoParser/ExprEmitter.cpp:769: M::KGEN::LIT::SRValue M::KGEN::LIT::ExprEmitter::emitSRValue(ASTExprAnd<M::KGEN::LIT::AnyValue>, M::KGEN::LIT::ExprContext, M::KGEN::LIT::ASTType): Assertion `pValue && "must be PValue if register-passable and not SRValue"' failed.

[Mogball]

This has been fixed at top-of-tree.