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).
49 lines
1.4 KiB
Plaintext
49 lines
1.4 KiB
Plaintext
// Protocol value as a field of a wrapper struct, constructed from a stack
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// local inside a function and appended to a `List`. The payload must be
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// heap-copied so dispatch survives the constructing function returning.
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#import "modules/std.sx";
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Sizable :: protocol {
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size :: () -> s64;
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}
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Widget :: struct { value: s64; }
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impl Sizable for Widget {
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size :: (self: *Widget) -> s64 { self.value }
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}
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// Wrapper struct with a protocol field (like ViewChild)
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Item :: struct {
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view: Sizable;
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}
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Container :: struct {
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items: List(Item);
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add :: (self: *Container, w: Widget) {
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p := w; // local copy
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self.items.append(Item.{ view = p }); // protocol created from stack local `p`
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// Works here: stack local `p` is still alive
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out("inside add: ");
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print("{}\n", self.items.items[self.items.len - 1].view.size());
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}
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}
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main :: () -> void {
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c : Container = .{};
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c.add(Widget.{ value = 42 });
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c.add(Widget.{ value = 99 });
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// BUG: items[0] should return 42, but returns 99 (reads items[1]'s stack slot)
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// Both protocol values point to the same stack address (the `p` local in add())
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r0 := c.items.items[0].view.size();
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r1 := c.items.items[1].view.size();
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print("items[0] = {} (expected 42)\n", r0);
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print("items[1] = {} (expected 99)\n", r1);
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// With more stack activity between add() and the reads, this crashes
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// (stack memory overwritten by other function calls)
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}
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