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).
33 lines
840 B
Plaintext
33 lines
840 B
Plaintext
// `cast(T) val` inside a conditional, evaluated by the IR interpreter
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// during a post-link callback. The `cast` syntax lowers the type arg
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// (`s64`) as a `placeholder` IR op; the interpreter treats placeholders
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// as undef so the comparison runs through unchanged.
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#import "modules/std.sx";
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#import "modules/compiler.sx";
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libc :: #library "c";
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popen :: (cmd: [:0]u8, mode: [:0]u8) -> *void #foreign libc;
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puts :: (s: [:0]u8) -> s32 #foreign libc;
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R :: struct { x: s32; }
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bug :: (cmd: [:0]u8) -> ?R {
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f := popen(cmd, "r");
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if cast(s64) f == 0 { return null; }
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R.{ x = 1 }
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}
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post_link :: () -> bool {
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if r := bug("echo hi") { puts("ok"); } else { puts("null"); }
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true
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}
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configure :: () {
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opts := build_options();
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opts.set_post_link_callback(post_link);
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}
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#run configure();
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main :: () { print("rt\n"); }
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