cgen, closures: `mut` capture of a pointer-alias type emits a one-deref-short member access

[medvednikov]

Description

When a closure captures a variable by mut whose type is an alias of a pointer (type AppRef = &App), cgen stores the capture in the closure context struct as a double pointer (AppRef* app;, i.e. App**), but the closure body emits only a single dereference (_V_closure_ctx->app->field). The C compiler then rejects the member access because _V_closure_ctx->app is itself a pointer.

A non-mut capture of the same alias compiles correctly, which isolates the extra (unaccounted-for) pointer level to the mut capture path.

V version: V 0.5.1, current master (5e36217f8)
OS/Backend: reproduced on macOS arm64; originally reported on Linux (a _V_closure_ctx->app member-reference error from a captured pointer).

Reproducer

struct App {
mut:
	score int
}

type AppRef = &App

fn make_handler(mut app AppRef) fn () {
	return fn [mut app] () {
		app.score++
	}
}

fn main() {
	mut a := App{}
	h := make_handler(mut &a)
	h()
}

Compile with:

v file.v

Current behavior

error: member reference base type 'main__AppRef' (aka 'struct main__App *') is not a structure or union
  _V_closure_ctx->app->score++;

The generated context struct field is main__AppRef* app; (a struct main__App **), but the body accesses it as _V_closure_ctx->app->score (one deref short). It should be either (*_V_closure_ctx->app)->score, or the field should be stored as main__AppRef (single pointer).

Expected behavior

The captured-pointer member access in the closure body should match the pointer level of the context-struct field, so the program compiles.

Notes

• Reported via the bugs.vlang.io crash reporter (a '_V_closure_ctx->app' is a pointer; did you mean to use '->'? variant from a captured pointer in a closure). This reproducer is the same closure-captured-pointer member-access family; the operator/pointer-level mismatch direction differs.

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