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Fix #121126: index out of bounds exceeds max value #123483

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Fix #121126: index out of bounds exceeds max value #123483

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44e66b6
Fix #121126: index out of bounds exceeds max value
c4rrao Apr 4, 2024
57a5b75
Merge branch 'rust-lang:master' into master
c4rrao May 22, 2024
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10 changes: 8 additions & 2 deletions compiler/rustc_mir_transform/src/known_panics_lint.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -102,8 +102,14 @@ impl<'tcx> Value<'tcx> {
}
(PlaceElem::Index(idx), Value::Aggregate { fields, .. }) => {
let idx = prop.get_const(idx.into())?.immediate()?;
let idx = prop.ecx.read_target_usize(idx).ok()?;
fields.get(FieldIdx::from_u32(idx.try_into().ok()?)).unwrap_or(&Value::Uninit)
let idx: u32 = prop.ecx.read_target_usize(idx).ok()?.try_into().ok()?;

let max: u32 = FieldIdx::MAX.index().try_into().ok()?;
if idx > max {
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Please implement this as a method on all index types instead. Like try_from_u32 and then implement from_u32 by using that

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Can we have from_u32 returning Option instead of Self? I can't see a way to inform the caller that the operation was unsuccessful without using Option, Result or panicking. And I guess Result is not the way and panicking was what we had before with the assert()

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Hmm... we could just always return an option, good point. Yea lets do that instead of my idea of having both a try_from and a from method

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I have a doubt here. In this match inside project method from Value type, why do we always cast the usize idx to a u32 just to call then from_u32 when we have also a from_usize method?

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probably just an oversight. using from_usize is better

return None;
}

fields.get(FieldIdx::from_u32(idx)).unwrap_or(&Value::Uninit)
}
(
PlaceElem::ConstantIndex { offset, min_length: _, from_end: false },
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13 changes: 13 additions & 0 deletions tests/ui/indexing/index-out-of-bounds-exceeds-max-value-issue-121126.rs
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@@ -0,0 +1,13 @@
// Regression test for #121126. Compiler was panicking when indexing an array
// with an index that is out of bounds and its value is greater than the max
// value allowed for an index.

//@ build-fail

fn main() {
[0][0xFFFF_FF01];
//~^ ERROR this operation will panic at runtime [unconditional_panic]
}

// NOTE: In order for the test to be valid, the index can take on any value
// between FieldIdx::MAX + 1 (= 0xFFF_FF01) and u32::MAX (= 0xFFF_FFFF)
10 changes: 10 additions & 0 deletions tests/ui/indexing/index-out-of-bounds-exceeds-max-value-issue-121126.stderr
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@@ -0,0 +1,10 @@
error: this operation will panic at runtime
--> $DIR/issue-121126-index-out-of-bounds-exceeds-max-value.rs:8:5
|
LL | [0][0xFFFF_FF01];
| ^^^^^^^^^^^^^^^^ index out of bounds: the length is 1 but the index is 4294967041
|
= note: `#[deny(unconditional_panic)]` on by default

error: aborting due to 1 previous error

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