issue(0140): comptime type-construction bail panics instead of diagnosing
A failing declare/define (e.g. empty variant list) bails correctly in
the interp, but evalComptimeType swallows last_bail_detail via
`catch return null`; the decl poisons to .unresolved with no diagnostic
and reaches LLVM emission -> panic ("unresolved type reached LLVM
emission"), or hides behind a misleading downstream cascade.
Pre-existing (plain define path), surfaced while starting the make_enum
step. Blocks make_enum's computed (pointer-backed) []EnumVariant slice
decode. Repro + investigation prompt filed; CHECKPOINT-METATYPE marked
BLOCKED. Session paused pending fix per CLAUDE.md IMPASSABLE rule.
This commit is contained in:
agra
@@ -74,10 +74,15 @@ in the always-loaded prelude interns them into every module's type table and
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shifts every `.ir` snapshot. On-demand import keeps the prelude clean.
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## Next step
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Pick any (independent):
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**BLOCKED on issue 0140** for the make_enum path (see Known issues). The other
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two are unblocked:
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- **`make_enum(variants: []EnumVariant)`** sx helper over a COMPUTED (non-literal)
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variant list — exercises the interpreter decoding a value-arg slice in `define`
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(vs. the literal `.[ … ]` the current examples use).
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(vs. the literal `.[ … ]` the current examples use). **BLOCKED:** a computed
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(pointer-backed) `[]EnumVariant` slice from a local var / `List` does not decode
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in `defineEnum`/`decodeVariantElements`, and the resulting interp bail is
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SWALLOWED (panic / misleading cascade, no root reason) — issue 0140. Fix 0140
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first so the decode failure surfaces cleanly, THEN implement the slice decode.
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- **Widen `type_info` / `TypeInfo` past `` `enum ``** — struct/tuple variants:
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add `` .`struct ``/`` .`tuple `` to the `TypeInfo` enum in `meta.sx`, teach
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`reflectTypeInfo` to build them, and teach `defineEnum` (→ a `defineType`) to
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@@ -87,9 +92,17 @@ Pick any (independent):
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self-reference already rejected — issue 0139.)
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## Known issues
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None. (issue 0139 — by-value self-reference segfault — RESOLVED: `checkInfiniteSize`
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Pass 1g emits a loud "infinitely sized" diagnostic + breaks the cycle; covers
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source + comptime types; `examples/1178` locks it.)
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- **issue 0140 (OPEN) — a failing comptime type construction panics instead of
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diagnosing.** `evalComptimeType` (`comptime.zig:~457`) swallows the interp's
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`last_bail_detail` via `catch return null`; callers poison to `.unresolved`
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with no diagnostic, and `.unresolved` reaches LLVM emission → panic ("unresolved
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type reached LLVM emission"), or rides behind a misleading downstream cascade.
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Pre-existing (plain `define` path; surfaced while starting make_enum). Repro:
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`issues/0140-*.sx`. Blocks the make_enum computed-slice step. **Session paused
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pending the fix** per the CLAUDE.md IMPASSABLE rule.
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- issue 0139 — by-value self-reference segfault — RESOLVED (`checkInfiniteSize`
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Pass 1g emits a loud "infinitely sized" diagnostic + breaks the cycle;
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`examples/1178` locks it).
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## Log
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- **`type_info($T)` reflection done (enum round-trip).** New `BuiltinId.type_info`;
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127
issues/0140-comptime-type-construction-bail-unresolved-panic.md
Normal file
127
issues/0140-comptime-type-construction-bail-unresolved-panic.md
Normal file
@@ -0,0 +1,127 @@
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# 0140 — a failing comptime type construction panics ("unresolved type reached LLVM emission") instead of diagnosing the bail
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## Symptom
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One-line: when a comptime type construction (`declare`/`define`) bails in the
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interpreter, the failure is swallowed — the decl is poisoned to `.unresolved`
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with **no diagnostic**, and that `.unresolved` reaches LLVM emission and panics
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instead of emitting a clean, build-gating error that names the bail reason.
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- **Observed:** `thread … panic: unresolved type reached LLVM emission — a type
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resolution failure was not diagnosed/aborted`
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(`src/backend/llvm/types.zig:176`, the `.unresolved` arm of `toLLVMTypeInfo`),
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reached from `emitAlloca` (`src/backend/llvm/ops.zig:329`) for the local
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`e : Empty = ---`. Exit 134 (panic), not a diagnostic.
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- **Expected:** a build-time `.err` at the construction site carrying the
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interpreter's bail detail — `defineEnum` already produces the precise reason
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("comptime define(): enum has no variants") via `bailDetail`, which sets
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`Interpreter.last_bail_detail`. Exit 1, no panic, message visible to the user.
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This is **PRE-EXISTING** and orthogonal to the METATYPE `type_info` work that
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surfaced it: the repro uses only the plain `define` path with an empty literal
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variant list (`type_info` is not involved). It reproduces for *any* comptime
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construction that bails — bad/empty `TypeInfo`, a `variants` value the decoder
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can't read (e.g. a pointer-backed `[]EnumVariant` slice built from a local
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variable / `List`, which is the next thing the make_enum step needs), etc.
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## Reproduction
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Minimal, standalone (only `modules/std.sx` + `modules/std/meta.sx`):
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```sx
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#import "modules/std.sx";
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#import "modules/std/meta.sx";
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Empty :: define(declare("Empty"), .enum(.{ variants = .[] }));
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main :: () -> i32 {
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e : Empty = ---;
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return 0;
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}
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```
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Run: `./zig-out/bin/sx run issues/0140-comptime-type-construction-bail-unresolved-panic.sx`
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→ panics today (exit 134); the fix should emit a diagnostic naming the bail
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reason and exit 1 (no panic).
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### Bisection (what does / does not trigger the *panic*)
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| Variant | Result |
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|---|---|
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| `Empty :: define(declare("Empty"), .enum(.{ variants = .[] }))` + a *local* `e : Empty` | **PANICS** (exit 134) |
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| same construction, but `Empty` is only *referenced as a type* (no value created) | poisons silently — often a confusing downstream cascade, no root reason |
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| a make_enum-style computed slice `define(declare(n), .enum(.{ variants = local_slice }))` then a `.variant` *literal* | exit 1 with `"cannot infer enum type for '.x'"` — the literal-inference error fires first and *incidentally* gates emission, so no panic, but the **real bail reason is still never shown** |
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So the panic specifically needs the `.unresolved` type to survive to emission
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(here via a local `alloca`); when some *other* diagnostic happens to fire first,
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the build aborts before emission and the panic is dodged — but in **every** case
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the actual interp bail reason (`last_bail_detail`) is lost and the user sees
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either a panic or a misleading follow-on, never the root cause.
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## Investigation prompt
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> A comptime type construction (`declare`/`define`, and reflection like
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> `type_info`) that bails in the interpreter is swallowed: the build either
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> panics at LLVM emission ("unresolved type reached LLVM emission") or shows a
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> misleading downstream cascade, instead of a clean diagnostic naming the bail
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> reason. Repro:
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> `issues/0140-comptime-type-construction-bail-unresolved-panic.sx` (panics,
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> exit 134 today; the fix should print a diagnostic with the bail reason and
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> exit 1 — no panic).
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>
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> Root area: `evalComptimeType` in `src/ir/lower/comptime.zig` (~line 457):
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>
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> ```zig
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> const result = interp.call(func_id, &.{}) catch return null;
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> return result.asTypeId();
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> ```
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>
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> The `catch return null` drops the interpreter's `last_bail_detail`
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> (`Interpreter.last_bail_detail`, `src/ir/interp.zig:218`, set by every
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> `bailDetail(...)` — e.g. `defineEnum`'s "enum has no variants"). The two
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> callers then poison to `.unresolved` with NO diagnostic:
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> - `src/ir/lower/decl.zig:777`: `const tid = self.evalComptimeType(cd.value) orelse TypeId.unresolved;`
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> then `putTypeAlias(..., .unresolved)`.
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> - `src/ir/lower/generic.zig:1762`: `orelse return .unresolved`.
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>
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> `.unresolved` is the correct *sentinel* (it trips the codegen tripwire so a
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> resolution failure can never silently ship), but here NOTHING converts it into
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> a user-facing diagnostic, so it either crashes at emit or rides along behind a
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> follow-on error.
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>
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> Suspected fix: in `evalComptimeType`, on the interp error path, emit a
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> diagnostic at the construction expression's span carrying `last_bail_detail`
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> (mirror how `src/ir/emit_llvm.zig:856` / `:933` already surface
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> `last_bail_detail` for `#run` / comptime-function evaluation —
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> `Interpreter.last_bail_detail orelse "<generic>"`). Reset
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> `last_bail_detail = null` before the call and read it after the `catch`. Return
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> `.unresolved` (keep the poison) *after* the diagnostic has been emitted, so the
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> build is gated with a real message and no `.unresolved` reaches emission
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> unannounced. Make sure BOTH callers (decl + generic) route through the
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> diagnostic — ideally emit inside `evalComptimeType` so neither caller can
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> forget. Do NOT swap `.unresolved` for a "reasonable-looking" default type
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> (per CLAUDE.md REJECTED PATTERNS); the sentinel + diagnostic is the right shape.
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>
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> Verification: the repro emits a diagnostic naming the bail reason and exits 1
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> (no panic); then `zig build && zig build test` green. Pin the repro as an
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> `11xx` diagnostics example (move to
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> `examples/11xx-diagnostics-comptime-type-construction-bail.sx`, seed the
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> `expected/*.exit` marker, capture with `-Dupdate-goldens`, review the diff).
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> Also add a positive note in `current/CHECKPOINT-METATYPE.md` that the
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> make_enum computed-slice step can proceed once this lands (the decoder's
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> "variants is not a slice/array" bail will then be a clean diagnostic instead
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> of a cascade/panic).
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## Notes
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- Tripwire site (symptom): `src/backend/llvm/types.zig:176` (`toLLVMTypeInfo`,
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`.unresolved` arm) via `emitAlloca` (`src/backend/llvm/ops.zig:329`).
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- Root area (cause): `evalComptimeType` `catch return null`
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(`src/ir/lower/comptime.zig:~457`) drops `last_bail_detail`; callers
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`decl.zig:777` / `generic.zig:1762` poison to `.unresolved` with no diagnostic.
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- The interpreter already computes the precise reason — `bailDetail` /
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`typeErrorDetail` set `Interpreter.last_bail_detail` (`interp.zig:218`); the
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`#run` path at `emit_llvm.zig:856` is the existing precedent for surfacing it.
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- Blocks: the make_enum computed-(non-literal)-variant-list step
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(`current/PLAN-METATYPE.md` Status), whose decode failures currently land in
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exactly this swallow.
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@@ -0,0 +1,20 @@
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// Repro for issue 0140 — a FAILING comptime type construction
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// (`define` with an empty variant list) bails correctly in the interp
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// ("comptime define(): enum has no variants"), but that bail is swallowed:
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// `evalComptimeType` returns null, the decl is poisoned to `.unresolved`
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// with NO diagnostic, and the `.unresolved` type reaches LLVM emission and
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// PANICS ("unresolved type reached LLVM emission") instead of surfacing a
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// clean error with the bail reason.
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//
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// Expected: a build-time diagnostic at the construction site naming the
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// bail reason (e.g. "comptime type construction failed: enum has no
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// variants"), exit 1, no panic.
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#import "modules/std.sx";
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#import "modules/std/meta.sx";
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Empty :: define(declare("Empty"), .enum(.{ variants = .[] }));
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main :: () -> i32 {
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e : Empty = ---;
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return 0;
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}
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