From 28ca6b0f79ebe238d1deb0c06b0b17396716b958 Mon Sep 17 00:00:00 2001
From: Michael Woerister <michaelwoerister@posteo>
Date: Wed, 16 Feb 2022 11:18:01 +0100
Subject: [PATCH] debuginfo: Support fat pointers to unsized tuples.

---
 .../rustc_codegen_llvm/src/debuginfo/utils.rs | 13 ++++-------
 src/test/debuginfo/unsized.rs                 | 23 +++++++++++++++++++
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/utils.rs b/compiler/rustc_codegen_llvm/src/debuginfo/utils.rs
index 6dd0d58efe3..acd032a7dc6 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/utils.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/utils.rs
@@ -6,7 +6,7 @@ use super::CrateDebugContext;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, DefIdTree, Ty};
-use rustc_target::abi::VariantIdx;
+use rustc_target::abi::Variants;
 
 use crate::common::CodegenCx;
 use crate::llvm;
@@ -72,20 +72,15 @@ pub(crate) fn fat_pointer_kind<'ll, 'tcx>(
     match *pointee_ty.kind() {
         ty::Str | ty::Slice(_) => Some(FatPtrKind::Slice),
         ty::Dynamic(..) => Some(FatPtrKind::Dyn),
-        ty::Adt(adt_def, _) => {
-            assert!(adt_def.is_struct());
-            assert!(adt_def.variants.len() == 1);
-            let variant = &adt_def.variants[VariantIdx::from_usize(0)];
-            assert!(!variant.fields.is_empty());
-            let last_field_index = variant.fields.len() - 1;
-
+        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);
-            assert!(unsized_field.is_unsized());
+            debug_assert!(unsized_field.is_unsized());
             fat_pointer_kind(cx, unsized_field.ty)
         }
         ty::Foreign(_) => {
diff --git a/src/test/debuginfo/unsized.rs b/src/test/debuginfo/unsized.rs
index ebd40f9dda2..7ccc88ef940 100644
--- a/src/test/debuginfo/unsized.rs
+++ b/src/test/debuginfo/unsized.rs
@@ -16,6 +16,14 @@
 // gdbg-check:$3 = {pointer = [...], vtable = [...]}
 // gdbr-check:$3 = &unsized::Foo<dyn core::fmt::Debug> {pointer: [...], vtable: [...]}
 
+// gdb-command:print tuple_slice
+// gdbg-check:$4 = {data_ptr = [...], length = 2}
+// gdbr-check:$4 = &(i32, i32, [i32]) {data_ptr: [...], length: 2}
+
+// gdb-command:print tuple_dyn
+// gdbg-check:$5 = {pointer = [...], vtable = [...]}
+// gdbr-check:$5 = &(i32, i32, dyn core::fmt::Debug) {pointer: [...], vtable: [...]}
+
 // === CDB TESTS ===================================================================================
 
 // cdb-command: g
@@ -34,6 +42,17 @@
 // cdb-check:    [+0x000] pointer          : 0x[...] [Type: unsized::Foo<dyn$<core::fmt::Debug> > *]
 // cdb-check:    [...] vtable           : 0x[...] [Type: unsigned [...]int[...] (*)[3]]
 
+// cdb-command:dx tuple_slice
+// cdb-check:tuple_slice      [Type: ref$<tuple$<i32,i32,slice$<i32> > >]
+// cdb-check:    [+0x000] data_ptr         : 0x[...] [Type: tuple$<i32,i32,slice$<i32> > *]
+// cdb-check:    [...] length           : 0x2 [Type: unsigned [...]int[...]
+
+// cdb-command:dx tuple_dyn
+// cdb-check:tuple_dyn        [Type: ref$<tuple$<i32,i32,dyn$<core::fmt::Debug> > >]
+// cdb-check:    [+0x000] pointer          : 0x[...] [Type: tuple$<i32,i32,dyn$<core::fmt::Debug> > *]
+// cdb-check:    [...] vtable           : 0x[...] [Type: unsigned [...]int[...] (*)[3]]
+
+#![feature(unsized_tuple_coercion)]
 #![feature(omit_gdb_pretty_printer_section)]
 #![omit_gdb_pretty_printer_section]
 
@@ -51,6 +70,10 @@ fn main() {
     let b: &Foo<Foo<[u8]>> = &foo;
     let c: &Foo<dyn std::fmt::Debug> = &Foo { value: 7i32 };
 
+    // Also check unsized tuples
+    let tuple_slice: &(i32, i32, [i32]) = &(0, 1, [2, 3]);
+    let tuple_dyn: &(i32, i32, dyn std::fmt::Debug) = &(0, 1, &3u64);
+
     zzz(); // #break
 }