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Add failing quickcheck-derived test case for refactor casts #1392

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Add failing quickcheck-derived test case for refactor casts #1392

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58df33e
c2rust-refactor: tests: factor out `verify_double_cast`
fw-immunant Oct 3, 2025
93e1243
c2rust-refactor: tests: print counterexample
fw-immunant Oct 3, 2025
882d68f
c2rust-refactor: tests: add `test_cast_i32_u32_ssize`
fw-immunant Oct 3, 2025
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102 changes: 65 additions & 37 deletions c2rust-refactor/src/transform/casts/tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -60,51 +60,79 @@ fn cast_tys<'bv>(bv: BV<'bv>, tys: &[SimpleTy], pw: PointerWidth) -> BV<'bv> {
tys.windows(2).fold(bv, |y, w| cast_bv(y, w[0], w[1], pw))
}

thread_local!(static Z3_CONFIG: Config = Config::new());
thread_local!(static Z3_CONFIG: Config = { let mut c = Config::new(); c.set_model_generation(true); c });
thread_local!(static Z3_CONTEXT: Context = Z3_CONFIG.with(|cfg| Context::new(cfg)));

quickcheck! {
// Verify `check_double_cast` using QuickCheck and Z3
fn verify_double_cast(pw: PointerWidth, tys: Vec<SimpleTy>) -> bool {
if tys.len() <= 1 {
return true;
}
#[test]
fn test_cast_i32_u32_ssize() {
verify_double_cast(
PointerWidth(64),
vec![
SimpleTy::Int(32, true),
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x as i32 as u32 as isize is not correct to shorten to x as i32 as usize because it would sign-extend, but isn't x as u32 as isize fine?

SimpleTy::Int(32, false),
SimpleTy::Size(true),
],
);
}

Z3_CONTEXT.with(|ctx| {
// Build a minimized list of types with double casts removed
let mut min_tys = vec![tys[0].clone()];
for ty in &tys[1..] {
assert!(!min_tys.is_empty());
if *ty == min_tys[min_tys.len() - 1] {
// Cast to the same type, ignore it
continue;
// Verify `check_double_cast` using Z3
fn verify_double_cast(pw: PointerWidth, tys: Vec<SimpleTy>) -> bool {
if tys.len() <= 1 {
return true;
}

Z3_CONTEXT.with(|ctx| {
// Build a minimized list of types with double casts removed
let mut min_tys = vec![tys[0].clone()];
for ty in &tys[1..] {
assert!(!min_tys.is_empty());
if *ty == min_tys[min_tys.len() - 1] {
// Cast to the same type, ignore it
continue;
}
if min_tys.len() < 2 {
min_tys.push(ty.clone());
continue;
}
let last2 = &min_tys[min_tys.len() - 2..];
match check_double_cast(last2[0], last2[1], *ty) {
DoubleCastAction::RemoveBoth => {
min_tys.pop();
}
if min_tys.len() < 2 {
min_tys.push(ty.clone());
continue;
DoubleCastAction::RemoveInner => {
*min_tys.last_mut().unwrap() = ty.clone();
}
let last2 = &min_tys[min_tys.len() - 2..];
match check_double_cast(last2[0], last2[1], *ty) {
DoubleCastAction::RemoveBoth => {
min_tys.pop();
}
DoubleCastAction::RemoveInner => {
*min_tys.last_mut().unwrap() = ty.clone();
}
DoubleCastAction::KeepBoth => {
min_tys.push(ty.clone());
}
DoubleCastAction::KeepBoth => {
min_tys.push(ty.clone());
}
}
}

let x = BV::new_const(&ctx, "x", ty_bit_width(tys[0], pw));
let y = cast_tys(x.clone(), &tys[..], pw);
let z = cast_tys(x, &min_tys[..], pw);
let x = BV::new_const(&ctx, "x", ty_bit_width(tys[0], pw));
let y = cast_tys(x.clone(), &tys[..], pw);
let z = cast_tys(x.clone(), &min_tys[..], pw);

// Check the full type list against the minimized one
let solver = Solver::new(&ctx);
solver.assert(&z._eq(&y).not());
solver.check() == SatResult::Unsat
})
// Check the full type list against the minimized one
let solver = Solver::new(&ctx);
solver.assert(&z._eq(&y).not());
if solver.check() == SatResult::Unsat {
true
} else {
let model = solver.get_model().unwrap();
panic!(
"{}b counterexample:\n{:?} =>\n {:?} via tys {tys:?} vs.\n {:?} via min_tys {min_tys:?}",
pw.0,
model.eval(&x, true).unwrap(),
model.eval(&y, true).unwrap(),
model.eval(&z, true).unwrap()
)
}
})
}

quickcheck! {
// Apply `verify_double_cast` to a sample of possible cast sequences using QuickCheck
fn quickcheck_double_cast(pw: PointerWidth, tys: Vec<SimpleTy>) -> bool {
verify_double_cast(pw, tys)
}
}
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