The generic-?? wrong-fallback was not in lowerNullCoalesce: coercing
?A -> ?B (differing payload, e.g. the ?i32->?i64 call-arg coercion when
instantiating unwrap_or(99, ?i32)) routed through .optional_wrap, which
unconditionally unwrapped the source and re-wrapped as ALWAYS-PRESENT, so
a null became present-zero everywhere (args, returns, field init,
var-decl, ??). Add a CoercionPlan.optional_to_optional (conversions.zig)
+ a presence-preserving arm in coerceMode (coerce.zig): has_value ->
present: unwrap+coerce-child+wrap-present; absent: constNull(dst); merge
via a dst_ty block param. lowerVarDecl gains a !src_is_optional guard so
an annotated x : ?B = <?A> routes through the same arm (also makes
aggregate-payload var-decl ?[3]i64->?[]i64 / ?Concrete->?Protocol work).
Alias-optional struct-literal default already works (grouping + 0166);
a 1-tuple default ?(i32,) ?? 5 now emits a clean diagnostic instead of an
LLVM PHI abort (no implicit scalar->1-tuple coercion per spec).
Regressions: optionals/0916 (generic ??), 0917 (alias struct default),
0918 (var-decl optional->optional), diagnostics/1202 (1-tuple default) +
a conversions.test.zig unit test. Verified by 3 adversarial reviews,
suite 798/0.
The Optional->Concrete unwrap classify rule treated ?i64 -> bool as
unwrap+narrow (both builtin), silently yielding false for every optional
(present or null). specs.md defines no implicit optional->bool
conversion. Reject it: conversions.zig adds an optional_to_bool_reject
plan (dst == bool, child != bool); coerce.zig emits a located diagnostic
suggesting '!= null'. Covers arg/field-init/return via the shared
coerceMode. The if-opt presence test (issue 0164) is a separate path,
untouched.
Regression: examples/diagnostics/1199-diagnostics-optional-to-bool.sx +
conversions.test.zig unit test. Verified by 3 adversarial reviews, suite
789/0. Filed adjacent issue 0179 (whole implicit ?T->concrete unwrap
family silently miscompiles a null optional; design-touching).
Surface rename of the signed integer family: s1..s64 become i1..i64
(u1..u64, usize, isize unchanged). 'string' keeps the s-prefix arm in
name classification; width parsing moves to the i-prefix arm next to
isize.
Internal TypeId tags follow the surface (.s8/.s16/.s32/.s64 ->
.i8/.i16/.i32/.i64), as do mono-key mangle fragments (ptr_i64,
tu_i64_bool) and all display/diagnostic formatting (i{d}).
Migrated in the same sweep: stdlib + examples + issue repros + FFI C
companions (shared symbol names like ffi_id_i64), expected
stdout/stderr/ir snapshots, specs.md, readme.md, CLAUDE.md/AGENTS.md,
implementation_plan.md, docs/, issue writeups. Vendored stb_image and
historical flow state left untouched.
zig build test: 426/426; examples suite: 595/595.
Coercion classification now lives in src/ir/conversions.zig behind a *Lowering
facade (CoercionResolver), mirroring CallResolver / GenericResolver /
ProtocolResolver. Two pure classifiers:
- classify(src, dst) -> CoercionPlan (15 kinds: no_op / unbox_any / box_any /
closure_to_fn_reject / tuple_elementwise / optional_unwrap / void_to_optional /
optional_wrap / erase_protocol / int_to_float / float_to_int / ptr_int_bitcast /
widen / narrow / none) — the built-in coercion ladder.
- classifyXX(src, dst) -> XXPlan (unbox_any / no_op / erase_protocol /
protocol_to_pointer / coerce) — the xx-operator head.
coerceToType and lowerXX now `switch (classify…)` then emit; branch order
mirrors the originals exactly and every arm reproduces the prior lowering — the
f32/f64 Any match dispatch, buildProtocolErasure (lowerXX) vs buildProtocolValue
(coerceToType), tuple/optional recursion, and the user-Into fallback + pointer
materialization + recursion-guard/diagnostics (which stay in lowerXX /
tryUserConversion). IR emission stays entirely in Lowering; the classifiers are
pure. lowerXX keeps the operand's lowered Ref type as src_ty. `.none` means no
built-in applies (pass through; the Into fallback runs) — no silent default.
New pub: isFloat / isIntEx / typeBitsEx / resolveConcreteTypeName (the classifier
reads them); coercionResolver() accessor. lower.zig net -54 lines.
conversions.test.zig drives CoercionResolver directly: the full classify ladder
(no-op, Any box/unbox, widen/narrow, int<->float, ptr<->int, optional
wrap/unwrap, void->optional, tuple, closure-reject, .none for two unrelated
structs), erase_protocol for a concrete source, and classifyXX (all 5 kinds incl.
protocol-to-pointer vs coerce and pointer-materialization -> coerce).
zig build, zig build test, tests/run_examples.sh (357/0) all green — no .ir churn.
