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Rollup merge of rust-lang#94242 - compiler-errors:fat-uninhabitable-p…
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…ointer, r=michaelwoerister

properly handle fat pointers to uninhabitable types

Calculate the pointee metadata size by using `tcx.struct_tail_erasing_lifetimes` instead of duplicating the logic in `fat_pointer_kind`. Open to alternatively suggestions on how to fix this.

Fixes rust-lang#94149

r? `@michaelwoerister` since you touched this code last, I think!
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Manishearth authored Feb 24, 2022
2 parents 1d665f4 + c73a2f8 commit 2c639e6
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Showing 4 changed files with 49 additions and 18 deletions.
5 changes: 4 additions & 1 deletion compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
Original file line number Diff line number Diff line change
Expand Up @@ -449,7 +449,10 @@ fn pointer_or_reference_metadata<'ll, 'tcx>(
// This is a thin pointer. Create a regular pointer type and give it the correct name.
debug_assert_eq!(
(thin_pointer_size, thin_pointer_align),
cx.size_and_align_of(ptr_type)
cx.size_and_align_of(ptr_type),
"ptr_type={}, pointee_type={}",
ptr_type,
pointee_type,
);

unsafe {
Expand Down
33 changes: 16 additions & 17 deletions compiler/rustc_codegen_llvm/src/debuginfo/utils.rs
Original file line number Diff line number Diff line change
Expand Up @@ -4,9 +4,9 @@ use super::namespace::item_namespace;
use super::CrateDebugContext;

use rustc_hir::def_id::DefId;
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::layout::{HasParamEnv, LayoutOf};
use rustc_middle::ty::{self, DefIdTree, Ty};
use rustc_target::abi::Variants;
use tracing::trace;

use crate::common::CodegenCx;
use crate::llvm;
Expand Down Expand Up @@ -63,38 +63,37 @@ pub(crate) fn fat_pointer_kind<'ll, 'tcx>(
cx: &CodegenCx<'ll, 'tcx>,
pointee_ty: Ty<'tcx>,
) -> Option<FatPtrKind> {
let layout = cx.layout_of(pointee_ty);
let pointee_tail_ty = cx.tcx.struct_tail_erasing_lifetimes(pointee_ty, cx.param_env());
let layout = cx.layout_of(pointee_tail_ty);
trace!(
"fat_pointer_kind: {:?} has layout {:?} (is_unsized? {})",
pointee_tail_ty,
layout,
layout.is_unsized()
);

if !layout.is_unsized() {
return None;
}

match *pointee_ty.kind() {
match *pointee_tail_ty.kind() {
ty::Str | ty::Slice(_) => Some(FatPtrKind::Slice),
ty::Dynamic(..) => Some(FatPtrKind::Dyn),
ty::Adt(..) | ty::Tuple(..) if matches!(layout.variants, Variants::Single { .. }) => {
let last_field_index = layout.fields.count() - 1;
debug_assert!(
(0..last_field_index)
.all(|field_index| { !layout.field(cx, field_index).is_unsized() })
);

let unsized_field = layout.field(cx, last_field_index);
debug_assert!(unsized_field.is_unsized());
fat_pointer_kind(cx, unsized_field.ty)
}
ty::Foreign(_) => {
// Assert that pointers to foreign types really are thin:
debug_assert_eq!(
cx.size_of(cx.tcx.mk_imm_ptr(pointee_ty)),
cx.size_of(cx.tcx.mk_imm_ptr(pointee_tail_ty)),
cx.size_of(cx.tcx.mk_imm_ptr(cx.tcx.types.u8))
);
None
}
_ => {
// For all other pointee types we should already have returned None
// at the beginning of the function.
panic!("fat_pointer_kind() - Encountered unexpected `pointee_ty`: {:?}", pointee_ty)
panic!(
"fat_pointer_kind() - Encountered unexpected `pointee_tail_ty`: {:?}",
pointee_tail_ty
)
}
}
}
Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
// check-pass
// compile-flags: -Cdebuginfo=2
// fixes issue #94149

#![allow(dead_code)]

pub fn main() {
let _ = Foo::<dyn FooTrait>::new();
}

pub struct Foo<T: FooTrait + ?Sized> {
base: FooBase,
value: T,
}

impl<T: FooTrait + ?Sized> Foo<T> {
pub fn new() -> Box<Foo<T>> {
todo!()
}
}

pub trait FooTrait {}

pub struct FooBase {
cls: Bar,
}

// Bar *must* be a fieldless enum
pub enum Bar {}

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