bdd0e96d78
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).
25 lines
685 B
Plaintext
25 lines
685 B
Plaintext
// Feature 1 — a pack argument that doesn't conform to the constraint protocol
|
|
// is a per-position error. `Naked` has no `impl Show`, so passing it to a
|
|
// `..xs: Show` pack is rejected (pointing at the offending argument).
|
|
|
|
#import "modules/std.sx";
|
|
|
|
Show :: protocol(T: Type) {
|
|
get :: (self: *Self) -> T;
|
|
}
|
|
IntBox :: struct { v: s64; }
|
|
impl Show(s64) for IntBox { get :: (self: *IntBox) -> s64 => self.v; }
|
|
|
|
Naked :: struct { x: s64; } // intentionally NOT `impl Show`
|
|
|
|
howmany :: (..xs: Show) -> s64 {
|
|
return xs.len;
|
|
}
|
|
|
|
main :: () -> s32 {
|
|
a := IntBox.{ v = 1 };
|
|
n := Naked.{ x = 2 };
|
|
print("{}\n", howmany(a, n)); // `n` does not conform to Show
|
|
0
|
|
}
|