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Rollup merge of #112810 - compiler-errors:dont-ice-on-bad-layout, r=wesleywiser

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Don't ICE on unnormalized struct tail in layout computation

1. We try to compute a `SizeSkeleton` even if a layout error occurs, but we really only need to do this if we get `LayoutError::Unknown`, since that means our type is too polymorphic to actually compute the full layout. If we have other errors, like `LayoutError::NormalizationError` or `LayoutError::Cycle`, then we can't really make any progress, since this represents an actual error.
2. Avoid using `normalize_erasing_regions` and `struct_tail_erasing_lifetimes` since those ICE on normalization errors, and since we may call `layout_of` in HIR typeck, we don't know for certain that we're on the happy path.

Fixes #112736
This commit is contained in:
Matthias Krüger 2023-06-23 19:39:58 +02:00 • committed by GitHub
commit cea5ae00d2
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6 changed files with 80 additions and 12 deletions
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35
compiler/rustc_ty_utils/src/layout.rs
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@ -145,17 +145,35 @@ fn layout_of_uncached<'tcx>(
return Ok(tcx.mk_layout(LayoutS::scalar(cx, data_ptr)));
}
let unsized_part = tcx.struct_tail_erasing_lifetimes(pointee, param_env);
let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type()
// Projection eagerly bails out when the pointee references errors,
// fall back to structurally deducing metadata.
&& !pointee.references_error()
{
let metadata_ty = tcx.normalize_erasing_regions(
let pointee_metadata = tcx.mk_projection(metadata_def_id, [pointee]);
let metadata_ty = match tcx.try_normalize_erasing_regions(
param_env,
tcx.mk_projection(metadata_def_id, [pointee]),
);
pointee_metadata,
) {
Ok(metadata_ty) => metadata_ty,
Err(mut err) => {
// Usually `<Ty as Pointee>::Metadata` can't be normalized because
// its struct tail cannot be normalized either, so try to get a
// more descriptive layout error here, which will lead to less confusing
// diagnostics.
match tcx.try_normalize_erasing_regions(
param_env,
tcx.struct_tail_without_normalization(pointee),
) {
Ok(_) => {},
Err(better_err) => {
err = better_err;
}
}
return Err(LayoutError::NormalizationFailure(pointee, err));
},
};
let metadata_layout = cx.layout_of(metadata_ty)?;
// If the metadata is a 1-zst, then the pointer is thin.
if metadata_layout.is_zst() && metadata_layout.align.abi.bytes() == 1 {
@ -163,10 +181,13 @@ fn layout_of_uncached<'tcx>(
}
let Abi::Scalar(metadata) = metadata_layout.abi else {
return Err(LayoutError::Unknown(unsized_part));
return Err(LayoutError::Unknown(pointee));
};
metadata
} else {
let unsized_part = tcx.struct_tail_erasing_lifetimes(pointee, param_env);
match unsized_part.kind() {
ty::Foreign(..) => {
return Ok(tcx.mk_layout(LayoutS::scalar(cx, data_ptr)));
@ -178,7 +199,7 @@ fn layout_of_uncached<'tcx>(
vtable
}
_ => {
return Err(LayoutError::Unknown(unsized_part));
return Err(LayoutError::Unknown(pointee));
}
}
};