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
1.5 KiB
Plaintext
35 lines
1.5 KiB
Plaintext
// Dead statements after a block-terminating statement (`return` / `raise`) are
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// dropped instead of being emitted into the already-closed basic block.
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// Regression (issue 0061): a bare `return X;` / `raise` mid-block closed the
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// LLVM basic block but lowering kept emitting the trailing statements into it
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// → "Terminator found in the middle of a basic block". The canonical failable
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// closure form `{ raise error.X; return x; }` tripped this, blocking ERR E5.1.
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//
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// The fix must NOT over-reach: a CONDITIONAL `if cond { return }` (and the
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// `inline if` pack form) leaves a fresh merge block, so its trailing statements
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// must still run — exercised by `clamp` / `pick` below.
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#import "modules/std.sx";
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E :: error { Neg }
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// dead `return 99;` after an unconditional return
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const_one :: () -> s64 { return 1; return 99; }
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// dead `return x;` after an unconditional raise (the failable closure shape)
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always_raise :: (x: s64) -> (s64, !E) { raise error.Neg; return x; }
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// guard: a conditional return must still fall through to the trailing return
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clamp :: (x: s64) -> s64 { if x > 10 { return 10; } return x; }
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main :: () -> s32 {
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print("const_one={}\n", const_one()); // 1
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print("raised={}\n", always_raise(5) catch e 0); // 0
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print("clamp_hi={}\n", clamp(42)); // 10
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print("clamp_lo={}\n", clamp(7)); // 7
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// dead code after a `return` at main's own block level is dropped.
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return 0;
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print("unreachable\n")
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}
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