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Layout error instead of an ICE for packed and aligned types #83319

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Jul 15, 2021
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Layout error instead of an ICE for packed and aligned types #83319

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9 changes: 7 additions & 2 deletions compiler/rustc_middle/src/ty/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -312,7 +312,8 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
let dl = self.data_layout();
let pack = repr.pack;
if pack.is_some() && repr.align.is_some() {
bug!("struct cannot be packed and aligned");
self.tcx.sess.delay_span_bug(DUMMY_SP, "struct cannot be packed and aligned");
return Err(LayoutError::Unknown(ty));
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Is it correct for this and below to return LayoutError::Unknown? Is the idea that it doesn't matter because an error will have already been emitted and the Unknown will never be emitted to the user?

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Conceptually returning LayoutError::Unknown does seems correct to me. At the same time it wouldn't be exactly the kind of error we would like to emit, given that it is relatively uninformative.

The general idea is that the incorrect use of packed & aligned will diagnosed elsewhere, before we reach any code that is in position to assume that failure to compute layout is an error or a bug (like codegen does assume).

}

let mut align = if pack.is_some() { dl.i8_align } else { dl.aggregate_align };
Expand Down Expand Up @@ -808,7 +809,11 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {

if def.is_union() {
if def.repr.pack.is_some() && def.repr.align.is_some() {
bug!("union cannot be packed and aligned");
self.tcx.sess.delay_span_bug(
tcx.def_span(def.did),
"union cannot be packed and aligned",
);
return Err(LayoutError::Unknown(ty));
}

let mut align =
Expand Down
11 changes: 11 additions & 0 deletions src/test/ui/conflicting-repr-hints.rs
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Expand Up @@ -66,4 +66,15 @@ union Z {
i: i32,
}

#[repr(packed, align(0x100))]
pub struct S(u16); //~ ERROR type has conflicting packed and align representation hints

#[repr(packed, align(0x100))]
pub union U { //~ ERROR type has conflicting packed and align representation hints
u: u16
}

static B: U = U { u: 0 };
static A: S = S(0);

fn main() {}
16 changes: 15 additions & 1 deletion src/test/ui/conflicting-repr-hints.stderr
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Expand Up @@ -74,7 +74,21 @@ LL | | i: i32,
LL | | }
| |_^

error: aborting due to 10 previous errors
error[E0587]: type has conflicting packed and align representation hints
--> $DIR/conflicting-repr-hints.rs:70:1
|
LL | pub struct S(u16);
| ^^^^^^^^^^^^^^^^^^

error[E0587]: type has conflicting packed and align representation hints
--> $DIR/conflicting-repr-hints.rs:73:1
|
LL | / pub union U {
LL | | u: u16
LL | | }
| |_^

error: aborting due to 12 previous errors

Some errors have detailed explanations: E0566, E0587, E0634.
For more information about an error, try `rustc --explain E0566`.