A block's value is now its last statement ONLY when that statement is a
trailing expression with no `;`. A trailing `;` discards the value,
leaving the block void. This makes value-vs-statement explicit and lets
the compiler reject "this block was supposed to produce a value".
Compiler:
- Parser records `Block.produces_value` (last stmt is a no-`;` trailing
expression) + `Block.discarded_semi` (the `;` that discarded a value),
via `expectSemicolonAfter`. A trailing expression before `}` may now
omit its `;` (previously a parse error). Match-arm and else-arm bodies
are built value-producing regardless of the arm `;` (arms are exempt —
the `;` is an arm terminator).
- Lowering: `lowerBlockValue` / the block-expr path / `inferExprType`
respect `produces_value`. A value-position block that discards its value
is a hard error (`lowerValueBody` for function bodies; the value-context
`.block` path for if/else branches, `catch` bodies, value bindings,
match arms). Pure-failable `-> !` bodies (value rides the error channel)
and a value-if whose branches are void are handled without false errors.
- `defer`/`onfail` cleanup bodies lower as statements (void), so a
trailing `;` there is fine.
Migration (behavior-preserving — output unchanged):
- stdlib + ~210 examples: dropped the trailing `;` on value-position last
expressions. `format` now ends with an explicit `#insert "return
result;"` (it relied on `#insert`-as-block-value, which `;` discards).
- Two `main :: () -> s32` examples that relied on the old silent
default-return got an explicit trailing `0`.
- Rejection snapshots 0412 / 1013 regenerated (their quoted source lines
lost a `;`); the diagnostics themselves are unchanged.
Docs/tests: specs.md "Block values" section; examples 0040 (rules) + 0041
(rejection); 3 parser unit tests. Filed issue 0066 (pre-existing
match-arm negated-literal phi-width quirk, surfaced not caused here).
Gates: zig build, zig build test, run_examples.sh -> 343 passed,
cross_compile.sh -> 7 passed (also refreshed its stale example names).
Pack/tuple spread now parses in tuple-value `(..xs)` / `(..xs.field)`,
tuple-type `(..F(Ts))` / `(..F(Ts.Arg))`, call-arg `f(..xs)` (already),
and closure-sig `Closure(..Ts)` / `Closure(..sources.T)` positions.
Design: the uniform spread node is the existing `spread_expr` (its
operand sub-expression carries the projection `xs.field` and
type-application `F(Ts)` shapes) rather than a new PackExpansion node —
call-arg slice-spread (`..arr`) and pack-spread (`..pack`) are
syntactically identical, so they must share one node, and spread_expr
already serves it with working slice lowering. Closure-sig packs gain
`ClosureTypeExpr.pack_projection` alongside the existing `pack_name`.
Parser-only; sema/lowering land in Phase 2. 6 new parser unit tests +
examples/probes/pack-expansion-parses.sx. Build + 225-suite green.
`..xs: Protocol` (a bare protocol, no `[]`, no `$`) on a variadic
parameter now parses to `ast.Param.is_pack = true` — a heterogeneous
protocol-constrained pack, distinct from a slice variadic
(`..xs: []T`, is_pack=false) and the comptime type-pack (`..$args`,
is_comptime=true). Parser-only: sema/lowering for the pack form land in
Phase 2; existing forms are unaffected (zero examples used a bare
non-slice variadic annotation). Adds three parser unit tests and
examples/probes/pack-param-parses.sx.
A tuple_init's element values must match its field types exactly — LLVM
`insertvalue` does no implicit conversion. An inferred `pair := (40, 2)`
lowered its elements under the enclosing fn's `target_type` (e.g. main's
s32 return), producing i32 values, while the field types were inferred
independently as s64. The {i64,i64} aggregate was filled with i32
constants, so reading any element back returned garbage (40 + 2^32) and
tuple equality was always false.
lowerTupleLiteral now lowers each element under its resolved field type
(the contextual target tuple's fields when present, else per-element
inference) and coerces to it, so value width always matches field width.
Assignment to a tuple-typed field/element now also propagates the target
tuple type. Adds examples/190-tuple-values.sx as a regression test and
examples/probes/tuple-baseline.sx as the Step 0.4 audit artifact.
