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).
35 lines
776 B
Plaintext
35 lines
776 B
Plaintext
// `?Protocol = null` — optional protocol boxes use sentinel-shape
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// (ctx == null is the "none" state), so they cost no extra storage
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// beyond the protocol's standard 2-pointer layout. Method calls on
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// a non-null optional protocol auto-unwrap and dispatch through the
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// vtable / inline fn-ptrs as usual.
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#import "modules/std.sx";
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GPU :: protocol {
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ping :: () -> s64;
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}
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Impl :: struct {}
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impl GPU for Impl {
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ping :: (self: *Impl) -> s64 { 42 }
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}
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main :: () -> s32 {
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g : ?GPU = null;
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if g != null {
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print("BAD: g not null at start\n");
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} else {
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print("g initially null\n");
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}
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g = xx @Impl.{};
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if g != null {
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n := g.ping();
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print("after assign: g.ping() = {}\n", n);
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} else {
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print("BAD: g still null after assign\n");
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}
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0
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}
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