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fix(0129): logical not is truthiness-aware, not a bit flip

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The unary .not arm emitted bool_not (LLVM bitwise Not) for every
operand. Correct on i1; on an error binding — an error-set value, u32
tag at the LLVM level — a bitwise not of a nonzero tag stays nonzero,
so 'if !e' held even on a SET error and its branch read the
uninitialized success value (real segfault in the distribution repo's
sqlite tests). Plain integers had the same hole ('!7' was '~7').

Now: bool keeps bool_not; integers and error-set operands lower as the
truthiness complement (cmp_eq against a typed zero); anything else is
diagnosed instead of silently bit-flipped.

Regression: examples/1057 (set error: !e must not hold; success: !e
holds with a real value; integer truthiness) + examples/1171 (!"text"
diagnosed); both FAIL pre-fix. zig build test 426/426;
tests/run_examples.sh 600/600.
This commit is contained in:
agra
2026-06-12 13:36:54 +03:00
parent ba37d0b393
commit a8fbded567
10 changed files with 148 additions and 1 deletions
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36
examples/1057-errors-negated-error-binding.sx Normal file
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@@ -0,0 +1,36 @@
// `!` on an error binding is the truthiness complement of `if e` (issue
// 0129). Pre-fix, `!` lowered as a bitwise not, so a nonzero error tag
// stayed nonzero and `if !e` held even on a SET error — with the success
// value read as garbage. Integer operands get the same `!x ≡ x == 0`
// semantics.
#import "modules/std.sx";
E :: error { Boom }
f :: (fail: bool) -> (i64, !E) {
if fail { raise error.Boom; }
return 42;
}
main :: () -> i32 {
// set error: `if e` holds, `if !e` must NOT
v, e := f(true);
took_e := false;
if e { took_e = true; }
if !e { print("BUG: !e held on a set error (v={})\n", v); return 1; }
if !took_e { print("BUG: if e did not hold on a set error\n"); return 2; }
// success: `if !e` holds and the value is real
v2, e2 := f(false);
if e2 { print("BUG: e2 set on success\n"); return 3; }
if !e2 { print("ok: !e2 on success, v2={}\n", v2); }
// integers: `!n` is `n == 0`, not a bit flip
n := 7;
if !n { print("BUG: !7 held\n"); return 4; }
z := 0;
if !z { print("ok: !0 holds\n"); }
print("done\n");
return 0;
}

10
examples/1171-diagnostics-logical-not-bad-operand.sx Normal file
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@@ -0,0 +1,10 @@
// `!` on an operand that has no truthiness (neither bool, integer, nor
// an error binding) is diagnosed instead of silently bit-flipped
// (issue 0129's diagnostic half).
#import "modules/std.sx";
main :: () -> i32 {
s := "text";
if !s { print("unreachable\n"); }
return 0;
}

1
examples/expected/1057-errors-negated-error-binding.exit Normal file
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@@ -0,0 +1 @@
0

1
examples/expected/1057-errors-negated-error-binding.stderr Normal file
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3
examples/expected/1057-errors-negated-error-binding.stdout Normal file
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@@ -0,0 +1,3 @@
ok: !e2 on success, v2=42
ok: !0 holds
done

1
examples/expected/1171-diagnostics-logical-not-bad-operand.exit Normal file
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@@ -0,0 +1 @@
1

5
examples/expected/1171-diagnostics-logical-not-bad-operand.stderr Normal file
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@@ -0,0 +1,5 @@
error: '!' needs a bool, integer, or error operand; got 'string'
--> examples/1171-diagnostics-logical-not-bad-operand.sx:8:8
|
8 | if !s { print("unreachable\n"); }
| ^^

1
examples/expected/1171-diagnostics-logical-not-bad-operand.stdout Normal file
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@@ -0,0 +1 @@

68
issues/0129-negated-error-binding-bitwise-not.md Normal file
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@@ -0,0 +1,68 @@
# RESOLVED — 0129: `if !e` held on a SET error binding (logical not lowered bitwise)
> **RESOLVED** (2026-06-12). Root cause: the `.not` arm of unary
> lowering (src/ir/lower/expr.zig) emitted `bool_not` — LLVM's bitwise
> `Not` — for EVERY operand type. On a real `i1` bool that is logical
> not; on an error binding (an error-set value, a u32 tag at the LLVM
> level) a bitwise not of a nonzero tag is still nonzero, so the branch
> condition stayed truthy: `if e` and `if !e` BOTH held on a set error,
> and the `!e` branch read the uninitialized success value. Plain
> integers had the same hole (`!7` was `~7` — truthy). Fix: `!` is now
> truthiness-aware — bool keeps `bool_not`; integers and error-set
> values lower as the complement `operand == 0` (`cmp_eq` against a
> typed zero); any other operand type is DIAGNOSED ("'!' needs a bool,
> integer, or error operand") instead of silently bit-flipped.
> Regression tests: `examples/1057-errors-negated-error-binding.sx`
> (set error: `!e` must not hold; success: `!e` holds with a real
> value; `!7`/`!0` integer truthiness) and
> `examples/1171-diagnostics-logical-not-bad-operand.sx` (`!"text"`
> diagnosed); both FAIL on pre-fix master. Gates: zig build test
> 426/426, tests/run_examples.sh 600/600.
## Symptom
`if e { ... }` on an error binding from a value-carrying failable
correctly tests "error is set", but `if !e { ... }` evaluates TRUE even
when the error IS set — both branches run, and the success value read
in the `!e` branch is uninitialized garbage.
Hit in production: /Users/agra/projects/distribution
`tests/sqlite_api.sx` (2026-06-12) — a `close()` behind `if !ne`
segfaulted on a garbage handle. The interim workaround routed negated
error logic through a plain bool.
## Reproduction
```sx
#import "modules/std.sx";
E :: error { Boom }
f :: (fail: bool) -> (i64, !E) {
if fail { raise error.Boom; }
return 42;
}
main :: () -> i32 {
v, e := f(true);
if e { print("error set\n"); }
if !e { print("BUG: !e true on a set error (v={})\n", v); return 1; }
return 0;
}
```
Observed at master ba37d0b: prints both lines, v is garbage, exits 1.
Expected: prints only "error set", exits 0.
## Investigation prompt
Suspected area: the unary `.not` lowering in src/ir/lower/expr.zig —
it emits `bool_not` (src/backend/llvm/ops.zig `emitBoolNot` →
`LLVMBuildNot`, a bitwise xor-with-all-ones) regardless of operand
type. Error bindings are error-set values backed by a u32 tag
(src/backend/llvm/types.zig lowers `.error_set` to i32), so `~tag` of
a set error is nonzero and the condition holds. Fix: make `!`
truthiness-aware (complement-of-zero for integer-backed operands), or
diagnose non-bool operands; silent wrong evaluation is the worst of
both. Verify with the repro plus an integer-truthiness case, and run
zig build test + tests/run_examples.sh.

23
src/ir/lower/expr.zig
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@@ -2030,7 +2030,28 @@ pub fn lowerExpr(self: *Lowering, node: *const Node) Ref {
self.suppress_int_fit_check = saved_fit;
break :blk switch (uop.op) {
.negate => self.builder.emit(.{ .neg = .{ .operand = operand } }, self.inferExprType(uop.operand)),
.not => self.builder.emit(.{ .bool_not = .{ .operand = operand } }, .bool),
// `!` is LOGICAL not. Only a real bool may go through the
// bitwise `bool_not` (i1); an integer-backed operand — an
// error binding (u32 tag), a plain integer — lowers as the
// truthiness complement `operand == 0`: a bitwise not of a
// nonzero tag stays nonzero, so `if !e` held even on a set
// error (issue 0129). Anything else is diagnosed.
.not => blk2: {
const oty = self.inferExprType(uop.operand);
if (oty == .bool) {
break :blk2 self.builder.emit(.{ .bool_not = .{ .operand = operand } }, .bool);
}
const int_like = self.isIntEx(oty) or
(!oty.isBuiltin() and self.module.types.get(oty) == .error_set);
if (int_like) {
const zero = self.builder.constInt(0, oty);
break :blk2 self.builder.emit(.{ .cmp_eq = .{ .lhs = operand, .rhs = zero } }, .bool);
}
if (self.diagnostics) |d| {
d.addFmt(.err, node.span, "'!' needs a bool, integer, or error operand; got '{s}'", .{self.formatTypeName(oty)});
}
break :blk2 self.builder.constBool(false);
},
.bit_not => self.builder.emit(.{ .bit_not = .{ .operand = operand } }, self.inferExprType(uop.operand)),
.xx => self.lowerXX(operand, uop.operand),
.address_of => blk2: {