fix: resolve qualified-import-member const as a compile-time constant (issue 0192)
A namespaced import's const (`m :: #import "lib.sx"; … m.CAP`) only ever resolved as a runtime value — the const folders in program_index.zig had no namespace-member arm, so a qualified const was rejected as an array dimension / Vector lane / generic value-param and could not seed another const, while the flat-import form worked everywhere. Add a `lookupQualifiedConst` (+ float / float-typed twins) ctx hook: resolve the alias via `namespaceAliasVerdictFrom` to its target module, then fold the member from that module's per-source const cache (`foldQualifiedConstInt` in lower/comptime.zig), pinned to the target source so nested const RHSs fold there. Wire it into evalConstIntExpr / evalConstFloatExpr / isFloatValuedExpr — both the expression-position field_access arm (`[m.CAP]T`) and the type-argument dotted-name arm (`Vector(m.LANES, …)`, generic value-params). Implemented on the source-aware ctxs (Lowering / SourceConstCtx); the namespace-blind ModuleConstCtx / StatelessInner return null, so a qualified-const dim reached only via the stateless type-alias path stays a clean unresolved-dim diagnostic, never a fabricated length. Resolves correctly for array dims, arithmetic, integral-float dims, Vector lanes, generic value-params, inline-for bounds, and struct fields. Regression: examples/modules/0842-modules-qualified-import-const-comptime.sx.
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issues/0192-qualified-import-const-not-comptime.md
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issues/0192-qualified-import-const-not-comptime.md
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# Issue 0192 — qualified-import-member const is not a compile-time constant
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> **✅ RESOLVED.** Root cause: the const folders in `src/ir/program_index.zig`
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> had no namespace-member arm — `evalConstIntExpr` resolved a bare/flat const
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> leaf (`lookupDimName`) but not a qualified `m.CAP`. Fix: a `lookupQualifiedConst`
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> (+ float / float-typed twins) ctx hook that resolves the alias `m` via
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> `Lowering.namespaceAliasVerdict` to its target module and folds `CAP` from
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> that module's per-source const cache (`foldQualifiedConstInt` in
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> `src/ir/lower/comptime.zig`), pinned to the target source so nested const RHSs
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> fold there. Wired into `evalConstIntExpr` / `evalConstFloatExpr` /
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> `isFloatValuedExpr` — both the EXPRESSION-position `field_access` arm (`[m.CAP]T`)
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> and the TYPE-argument dotted-name arm (`Vector(m.LANES, …)`, generic
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> value-params). Implemented on the source-aware ctxs (`Lowering` /
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> `SourceConstCtx`); the namespace-blind `ModuleConstCtx` / `StatelessInner`
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> return null (documented — a qualified-const dim reached ONLY via the stateless
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> type-alias path stays a clean unresolved-dim diagnostic, never a fabricated
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> length). Regression: `examples/modules/0842-modules-qualified-import-const-comptime.sx`
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> (qualified const as array dim, arithmetic, integral-float dim, Vector lane,
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> generic value-param, inline-for bound). Suite green 816/0.
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>
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> NOTE: the writeup's secondary symptom `A :: m.CAP` (a const aliasing a
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> qualified const) is NOT part of this bug — `A :: B` (aliasing a *bare* local
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> const) fails identically, so const-aliasing-a-single-name is a separate
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> pre-existing limitation (`N :: M + 1` expression-RHS works). Out of scope here.
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## Symptom
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A constant reached through a **namespaced (qualified) import** — `m :: #import
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"lib.sx"; … m.CAP` — is not recognized as a compile-time constant. It works
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fine as a *runtime* value, but the moment a comptime context needs it the
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compiler either rejects it or fails to resolve it:
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- as an **array dimension** → `error: array dimension must be a compile-time
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integer constant`
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- seeding **another const** (`A :: m.CAP;`) → `error: unresolved 'A'`
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Expected: a qualified-import const should fold to a compile-time constant
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everywhere a flat-imported const does — array dimensions, `Vector` lanes,
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const initializers, value-param args. (A **flat** `#import` of the same const
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works in all those positions; only the qualified `m.CONST` form fails.)
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## Reproduction
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Two files (the bug requires a *qualified* import, which needs a second module).
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`issues/0192-qualified-import-const-not-comptime/lib.sx`:
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```sx
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CAP :: 8;
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```
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`issues/0192-qualified-import-const-not-comptime.sx`:
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```sx
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m :: #import "0192-qualified-import-const-not-comptime/lib.sx";
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main :: () -> i64 {
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buf : [m.CAP]u8 = ---; // ← error: array dimension must be a compile-time integer constant
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return buf.len;
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}
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```
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```sh
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./zig-out/bin/sx run issues/0192-qualified-import-const-not-comptime.sx
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```
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Scoping probes (all run against the same `CAP :: 8`):
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| Form | Result |
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|------|--------|
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| `#import "lib.sx"; [CAP]u8` (flat, as dim) | ✅ works |
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| `m :: #import "lib.sx"; [m.CAP]u8` (qualified, as dim) | ❌ "array dimension must be a compile-time integer constant" |
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| `m :: #import …; A :: m.CAP;` (qualified, seeding a const) | ❌ "unresolved 'A'" |
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| `m :: #import …; x := m.CAP;` (qualified, runtime value) | ✅ works (prints 8) |
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So the value *is* reachable; only its **compile-time folding through the
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qualified member-access path** is missing.
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## Investigation prompt
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The compile-time integer folder is `evalConstIntExpr` in
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`src/ir/program_index.zig` (≈ line 318). Its `.identifier` arm resolves a
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flat-scope const via `ctx.lookupDimName(id.name)` — that is why a flat import
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works. Its `.field_access` arm (≈ line 325) only handles three shapes:
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`<pack>.len`, `<IntType>.min`/`.max` (via `TypeResolver.integerLimitFor`), and
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`<struct-const>.field` (via `ctx.lookupConstStructField`). There is **no arm
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that resolves a namespace-member const** — for `m.CAP`, `obj_name == "m"`,
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`fa.field == "CAP"`, none of the three match, and it falls through to `null` →
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`.not_const` → the array-dim diagnostic. The const-init path
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(`A :: m.CAP` → `unresolved 'A'`) is the same gap one layer up: the const
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initializer can't fold `m.CAP` either.
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The fix likely needs a new `ctx` hook — e.g. `lookupQualifiedConst(namespace,
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name) -> ?i64` — that follows the namespace edge (the import-alias `m` →
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its module, via `namespace_edges` / `module_decls` in `ProgramIndex`) to the
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imported module and returns the named const's folded integer value. Wire it
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into `evalConstIntExpr`'s `.field_access` arm: when `obj_name` names a known
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import namespace (not a pack / type / struct-const), look the field up as a
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module-level const in that namespace's module. The same resolution should make
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`A :: m.CAP` fold (whatever const-init folding path also routes through, or a
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sibling of, `evalConstIntExpr`).
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Mirror the existing `lookupConstStructField` plumbing — it already threads a
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"resolve a name's const value from another scope" capability through the
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`ModuleConstCtx` / `Lowering` ctx; the qualified-namespace case is the analogous
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"resolve a const from an imported module by alias" lookup. Watch the
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float sibling `evalConstFloatExpr` (≈ line 443) and `isFloatValuedExpr`
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(≈ line 264) — a qualified float const (`m.PI`) has the identical gap, so fix
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the cluster consistently (per the comment at line 332 about keeping the const
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cluster in agreement).
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## Verification step
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After the fix, the reproduction above should compile and run, printing exit
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code `8` (`buf.len`). Add a regression example exercising a qualified-import
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const as (a) an array dimension and (b) a const initializer. Then unblock the
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**linux epoll** work (CHECKPOINT-FIBERS): `library/modules/std/net/epoll.sx`
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wants `[N * ep.EV_SIZE]u8` event buffers sized from a qualified-import layout
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const — the cleanest expression of the arch-dependent `epoll_event` stride.
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## Discovered by
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Building `library/modules/std/net/epoll.sx` (the linux epoll twin of
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`std/net/kqueue.sx`, CHECKPOINT-FIBERS deferred follow-up). The epoll event
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buffer wants to be sized `[MAXEV * ep.EV_SIZE]u8` from the bindings module's
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arch-dependent stride const; `ep.EV_SIZE` as an array dimension hit this bug.
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A struct-based layout (`EpollEvent` with arch-branched u32 fields) sidesteps
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it, but per the project's STOP rule the workaround is not landed — the bindings
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work is paused pending this fix.
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