From 6a1f9e6fc7272599de76fec37e31db4978780649 Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Sun, 26 Dec 2021 22:12:41 +0800
Subject: [PATCH 1/3] mangling_v0: Update tests for the rust-demangler tool

---
 src/tools/rust-demangler/tests/lib.rs | 32 +++++++++++++--------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/src/tools/rust-demangler/tests/lib.rs b/src/tools/rust-demangler/tests/lib.rs
index 5a67b42322535..85019df7867dd 100644
--- a/src/tools/rust-demangler/tests/lib.rs
+++ b/src/tools/rust-demangler/tests/lib.rs
@@ -29,14 +29,14 @@ cc[4d6468d6c9fd4bb3]::spawn::{closure#0}::{closure#0}
 <core[846817f741e54dfd]::slice::Iter<u8> as core[846817f741e54dfd]::iter::iterator::Iterator>::rposition::<core[846817f741e54dfd]::slice::memchr::memrchr::{closure#1}>::{closure#0}
 alloc[f15a878b47eb696b]::alloc::box_free::<dyn alloc[f15a878b47eb696b]::boxed::FnBox<(), Output = ()>>
 INtC8arrayvec8ArrayVechKj7b_E
-<const_generic[317d481089b8c8fe]::Unsigned<11: u8>>
-<const_generic[317d481089b8c8fe]::Signed<152: i16>>
-<const_generic[317d481089b8c8fe]::Signed<-11: i8>>
-<const_generic[317d481089b8c8fe]::Bool<false: bool>>
-<const_generic[317d481089b8c8fe]::Bool<true: bool>>
-<const_generic[317d481089b8c8fe]::Char<'v': char>>
-<const_generic[317d481089b8c8fe]::Char<'\n': char>>
-<const_generic[317d481089b8c8fe]::Char<'∂': char>>
+<const_generic[317d481089b8c8fe]::Unsigned<11u8>>
+<const_generic[317d481089b8c8fe]::Signed<152i16>>
+<const_generic[317d481089b8c8fe]::Signed<-11i8>>
+<const_generic[317d481089b8c8fe]::Bool<false>>
+<const_generic[317d481089b8c8fe]::Bool<true>>
+<const_generic[317d481089b8c8fe]::Char<'v'>>
+<const_generic[317d481089b8c8fe]::Char<'\n'>>
+<const_generic[317d481089b8c8fe]::Char<'∂'>>
 <const_generic[317d481089b8c8fe]::Foo<_>>::foo::FOO
 foo[0]
 foo[0]
@@ -51,14 +51,14 @@ cc::spawn::{closure#0}::{closure#0}
 <core::slice::Iter<u8> as core::iter::iterator::Iterator>::rposition::<core::slice::memchr::memrchr::{closure#1}>::{closure#0}
 alloc::alloc::box_free::<dyn alloc::boxed::FnBox<(), Output = ()>>
 INtC8arrayvec8ArrayVechKj7b_E
-<const_generic::Unsigned<11: u8>>
-<const_generic::Signed<152: i16>>
-<const_generic::Signed<-11: i8>>
-<const_generic::Bool<false: bool>>
-<const_generic::Bool<true: bool>>
-<const_generic::Char<'v': char>>
-<const_generic::Char<'\n': char>>
-<const_generic::Char<'∂': char>>
+<const_generic::Unsigned<11u8>>
+<const_generic::Signed<152i16>>
+<const_generic::Signed<-11i8>>
+<const_generic::Bool<false>>
+<const_generic::Bool<true>>
+<const_generic::Char<'v'>>
+<const_generic::Char<'\n'>>
+<const_generic::Char<'∂'>>
 <const_generic::Foo<_>>::foo::FOO
 foo[0]
 foo[0]

From 1b8daf8c58267a5d9fae2021a311dfbbda11b02f Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Mon, 27 Dec 2021 20:05:22 +0800
Subject: [PATCH 2/3] mangling_v0: Add a test for mangling of foreign types

---
 src/test/ui/symbol-names/foreign-types.rs     | 19 ++++++++++++++++++
 src/test/ui/symbol-names/foreign-types.stderr | 20 +++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 src/test/ui/symbol-names/foreign-types.rs
 create mode 100644 src/test/ui/symbol-names/foreign-types.stderr

diff --git a/src/test/ui/symbol-names/foreign-types.rs b/src/test/ui/symbol-names/foreign-types.rs
new file mode 100644
index 0000000000000..33c5e6adfef29
--- /dev/null
+++ b/src/test/ui/symbol-names/foreign-types.rs
@@ -0,0 +1,19 @@
+// build-fail
+// compile-flags: -Z symbol-mangling-version=v0
+
+#![feature(extern_types)]
+#![feature(rustc_attrs)]
+
+extern "C" {
+    type ForeignType;
+}
+
+struct Check<T: ?Sized>(T);
+
+#[rustc_symbol_name]
+//~^ ERROR symbol-name(_RMCs
+//~| ERROR demangling(<foreign_types[
+//~| ERROR demangling-alt(<foreign_types::Check<foreign_types::ForeignType>>)
+impl Check<ForeignType> {}
+
+fn main() {}
diff --git a/src/test/ui/symbol-names/foreign-types.stderr b/src/test/ui/symbol-names/foreign-types.stderr
new file mode 100644
index 0000000000000..c6c59a6c82ea7
--- /dev/null
+++ b/src/test/ui/symbol-names/foreign-types.stderr
@@ -0,0 +1,20 @@
+error: symbol-name(_RMCsCRATE_HASH_13foreign_typesINtB<REF>_5CheckNvNtB<REF>_011ForeignTypeE)
+  --> $DIR/foreign-types.rs:13:1
+   |
+LL | #[rustc_symbol_name]
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling(<foreign_types[HASH]::Check<foreign_types[HASH]::ForeignType>>)
+  --> $DIR/foreign-types.rs:13:1
+   |
+LL | #[rustc_symbol_name]
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling-alt(<foreign_types::Check<foreign_types::ForeignType>>)
+  --> $DIR/foreign-types.rs:13:1
+   |
+LL | #[rustc_symbol_name]
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+

From 333a5cc3691a96aab461ebcbc6064ee79356f1ae Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Mon, 27 Dec 2021 20:09:20 +0800
Subject: [PATCH 3/3] mangling_v0: Skip extern blocks during mangling

---
 compiler/rustc_symbol_mangling/src/v0.rs      | 6 +++---
 src/test/ui/symbol-names/foreign-types.rs     | 2 +-
 src/test/ui/symbol-names/foreign-types.stderr | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/compiler/rustc_symbol_mangling/src/v0.rs b/compiler/rustc_symbol_mangling/src/v0.rs
index c2519adcbe416..fbb9e28d182f8 100644
--- a/compiler/rustc_symbol_mangling/src/v0.rs
+++ b/compiler/rustc_symbol_mangling/src/v0.rs
@@ -771,9 +771,9 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
         disambiguated_data: &DisambiguatedDefPathData,
     ) -> Result<Self::Path, Self::Error> {
         let ns = match disambiguated_data.data {
-            // FIXME: It shouldn't be necessary to add anything for extern block segments,
-            // but we add 't' for backward compatibility.
-            DefPathData::ForeignMod => 't',
+            // Extern block segments can be skipped, names from extern blocks
+            // are effectively living in their parent modules.
+            DefPathData::ForeignMod => return print_prefix(self),
 
             // Uppercase categories are more stable than lowercase ones.
             DefPathData::TypeNs(_) => 't',
diff --git a/src/test/ui/symbol-names/foreign-types.rs b/src/test/ui/symbol-names/foreign-types.rs
index 33c5e6adfef29..8f5b07769caff 100644
--- a/src/test/ui/symbol-names/foreign-types.rs
+++ b/src/test/ui/symbol-names/foreign-types.rs
@@ -1,5 +1,5 @@
 // build-fail
-// compile-flags: -Z symbol-mangling-version=v0
+// compile-flags: -C symbol-mangling-version=v0
 
 #![feature(extern_types)]
 #![feature(rustc_attrs)]
diff --git a/src/test/ui/symbol-names/foreign-types.stderr b/src/test/ui/symbol-names/foreign-types.stderr
index c6c59a6c82ea7..fcffdd2a8ec15 100644
--- a/src/test/ui/symbol-names/foreign-types.stderr
+++ b/src/test/ui/symbol-names/foreign-types.stderr
@@ -1,4 +1,4 @@
-error: symbol-name(_RMCsCRATE_HASH_13foreign_typesINtB<REF>_5CheckNvNtB<REF>_011ForeignTypeE)
+error: symbol-name(_RMCsCRATE_HASH_13foreign_typesINtB<REF>_5CheckNvB<REF>_11ForeignTypeE)
   --> $DIR/foreign-types.rs:13:1
    |
 LL | #[rustc_symbol_name]