sx/issues/0112-int-literal-out-of-range-silent-wrap.md

0112 — out-of-range int literal silently wraps into a narrower annotated target

Symptom. An integer literal that does not fit its explicitly-annotated integer target truncates with no diagnostic: x : s8 = 300; binds 44, y : u8 = 256; binds 0. Expected: a compile-time error (the value is known exactly at compile time; this is the integer analogue of the float→int narrowing rule, which errors on non-exact y : s64 = 1.5).

Split from issue 0111 (whose fix removed the implicit narrowing — an unannotated x := 0 no longer adopts the fn return type — but the explicit annotation path keeps wrapping).

Reproduction

#import "modules/std.sx";

main :: () {
    x : s8 = 300;
    print("x: {}\n", x);
    y : u8 = 256;
    print("y: {}\n", y);
}

• Observed (current master): prints x: 44 / y: 0, exit 0, no diagnostic.
• Expected: compile error per literal, e.g. integer literal 300 does not fit in s8 (range -128..127), and the analog for 256 / u8 (range 0..255).

Repro co-located: issues/0112-int-literal-out-of-range-silent-wrap.sx (unpinned until fixed).

Root cause (suspected area)

src/ir/lower/expr.zig .int_literal arm (~1499): when target_type is an integer type, it emits constInt(lit.value, tt) with no fits-check — the value truncates at LLVM emission width. The annotated-decl path (lowerVarDecl with type_annotation, src/ir/lower/stmt.zig ~255) sets target_type to the annotation before lowering the initializer, so every annotated narrow decl funnels through this arm. Assignments to narrow lvalues (b = 300 where b: s8) reach the same arm via lowerAssignment's LHS-derived target and likely need the same check.

Investigation prompt (paste into a fresh session)

Fix issue 0112: an int literal that does not fit its integer target type silently wraps. In the .int_literal arm of lowerExpr (src/ir/lower/expr.zig ~1499), before adopting an integer target_type, range-check lit.value against the target's signedness/width (the type table knows both; mirror the bounds logic used by TypeResolver.integerLimitFor). On overflow emit a diagnostic via self.diagnostics.addFmt(.err, node.span, ...) naming the literal, the type, and its range — do NOT silently fall back to s64 (REJECTED PATTERNS: no silent fallback defaults); still return a constInt of the target type so lowering continues to surface further errors. Audit sibling literal sinks that bypass this arm (comptime folds, lowerStructConstant, global initializers) for the same check.

Verify: issues/0112-int-literal-out-of-range-silent-wrap.sx errors with two diagnostics (s8/300, u8/256); boundary values still compile (x : s8 = -128 / 127, y : u8 = 0 / 255, m : u64 large literals). zig build && zig build test && bash tests/run_examples.sh — any example that relied on silent wrapping must be reviewed individually. Promote the repro per the resolution flow (likely examples/11xx-diagnostics-...).