sx/issues/0046-comptime-fn-nested-print-with-return.md

**FIXED.** `createComptimeFunction` now saves/restores the
outer `lowerComptimeCall`'s state — specifically
`inline_return_target`, `pack_arg_nodes`, `pack_param_count`,
`pack_arg_types`, `comptime_param_nodes`, `block_terminated`,
`target_type`, and `func_defer_base` — so the wrapper fn it
builds for the nested comptime expression runs in isolation.
Without the saves, the wrapper inherited an inline-return slot
belonging to a different basic block; the interp executed it
and tripped a null pointer store at `storeAtRawPtr`.

The pack-fn face of this bug (filed as face 2) was fixed
incidentally by step 2b's mono refactor — pack-fn calls
bypass the inline-return-slot setup entirely. Plain
`($x: s32)` comptime fns stay on the inline path; the
`createComptimeFunction` save/restore fix covers that path.

Regression test:
[examples/issue-0046.sx](../examples/issue-0046.sx).

# Symptom

A comptime fn body containing BOTH a nested comptime call
(e.g. `print(...)`) AND a `return X;` statement fails in one of
two shapes depending on the comptime-param flavour:

| Outer fn shape | Failure |
|---|---|
| `helper :: ($x: s32) -> s64 { print("inside\n"); return 42; }` (plain comptime) | Panic: `cast causes pointer to be null` at `src/ir/interp.zig:207 storeAtRawPtr`. |
| `dump :: (..$args) -> s64 { n := args[0]; print("got {}\n", n); return n; }` (pack-fn) | Compile error: `unresolved 'result'` at fake span `1:5` (inside the inserted code). |

Both vanish if you remove either the nested `print(...)` OR the
`return X;` statement:
- Arrow-form bodies (`=> expr`) work.
- Bodies with `return` but no nested comptime call work.
- Bodies with a nested comptime call but no `return` work.

Both faces share one root: my fix for issue-0045 (commit
`9e78790`) added an `inline_return_target` slot + alloca in
`lowerComptimeCall`, which is now active when the outer call's
body recursively invokes another comptime fn that itself runs
the `#insert build_format(fmt)` → interpreter → parse-and-lower
pipeline.

Pre-fix this pattern crashed too — at the LLVM verifier with
"Terminator found in the middle of a basic block" — because the
outer `return` emitted `ret X` into the caller's basic block
mid-flight. My fix routed `return` into the slot so the outer
body now fully completes, which means the recursive comptime
call runs to completion too. The interpreter / #insert scope
chain then has to be correct in this newly-reachable context,
and it isn't.

# Reproduction

```sx
#import "modules/std.sx";

// Face 1 — interp panic:
helper :: ($x: s32) -> s64 {
    print("inside\n");
    return 42;
}

// Face 2 — "unresolved 'result'":
dump :: (..$args) -> s64 {
    n : s64 = args[0];
    print("got {}\n", n);
    return n;
}

main :: () -> s32 {
    n := helper(7);        // ← panic in interp
    print("{}\n", dump(7)); // ← "unresolved 'result'"
    return 0;
}
```

Each face reproduces independently — they don't need to coexist
in the same program.

# What's NOT happening

- Not a regression introduced by issue-0045's fix per se: the
  same pattern hit a different fatal stage (LLVM verifier) before
  the fix. The fix exposed it; it didn't create it.
- Not caused by step 2a (pack typed indexing, commit `cd36784`):
  Face 1 reproduces with a plain `($x: s32)` comptime fn, no
  pack involved.
- Not exercised by any test in the suite today. `format`/`print`
  use arrow form or `#insert`-only bodies — no `return` in a
  block. User code historically followed the same pattern.

# Why this didn't block step 2a

Step 2a only tests `args[$i]` in arrow-form pack bodies and
arithmetic chains. No nested comptime call in any test body.
Step 2b (per-mono mangling) and step 3 (type-reflection
intrinsics, `$args[$i]` in type positions) don't inherently
require nested comptime calls either — builder fns run inside
`#insert` contexts, not inside the public pack-fn body, so
they have a different lowering path.

The pattern WILL bite when:
- Step 5 of the pack plan refactors stdlib's `print`/`format` to
  use `..$args` — print's body itself becomes the outer comptime
  fn that nests comptime calls.
- User code writes a pack-fn that wants both `print` for debug
  output AND `return X;` for early exit.

# Investigation prompt

For a fresh session picking this up:

The interaction is between (a) my issue-0045 `inline_return_target`
slot + alloca setup in `lowerComptimeCall` and (b) the recursive
comptime path that invokes `#insert build_format(fmt)` →
`evalComptimeString` → `createComptimeFunction` → `interp.call`
on a wrapper fn, then parses the returned source string and
lowers each parsed statement into the current scope.

Three angles worth probing:

1. **Saved/restored state in `createComptimeFunction`** at
   `src/ir/lower.zig:8851+`. It saves `builder.func`,
   `builder.current_block`, `builder.inst_counter`, `self.scope`,
   `current_ctx_ref`. It does NOT save/restore
   `inline_return_target`, `pack_arg_nodes`, `comptime_param_nodes`.
   The first two were added by my recent commits (`9e78790`,
   `cd36784`). One of these leaking into the wrapper-fn lowering
   is the most likely cause of Face 1.

2. **Ref numbering** — the alloca I added for `ret_slot` shifts
   subsequent Ref values in the outer fn (main). The interp
   shouldn't see those refs (it executes the wrapper fn's IR,
   not main's), but check whether the wrapper fn carries a stale
   Ref handle from the outer build context.

3. **Scope chain visible to parsed `#insert` statements**. For
   Face 2 the inserted code declares `result := ""` then references
   `result` in the next stmt. The lookup fails. Maybe the
   `lowerBlockValue` exit defer fires the parent scope deinit
   before the next stmt lowers — or `block_terminated` from the
   inline-return slot setup is interfering with the inserted-stmt
   loop in `lowerInsertExprValue`
   (`src/ir/lower.zig:7065+`).

A reasonable starting place: add the missing save/restore for
`inline_return_target` (and `pack_arg_nodes`) in
`createComptimeFunction`, then re-run both repros. If Face 1
disappears, that confirms angle 1.

# Verification

```sh
./zig-out/bin/sx run /tmp/issue-0046-face1.sx  # expect "n=42"
./zig-out/bin/sx run /tmp/issue-0046-face2.sx  # expect "got 7\n7"
```

Full suite + zig test must still pass after the fix.