Rollup merge of #145033 - nnethercote:fix-144994, r=fmease

Reimplement `print_region` in `type_name.rs`.
Broken by #144776; this is reachable after all.
Fixes#144994.
The commit also adds a lot more cases to the `type-name-basic.rs`, because it's currently very anaemic. This includes some cases where region omission does very badly; these are marked with FIXME.
r? `@fmease`

Author: Zalathar

compiler/rustc_const_eval/src/util/type_name.rs

@@ -18,7 +18,9 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
 }
 
 fnprint_region(&mutself,_region: ty::Region<'_>) -> Result<(),PrintError>{
-unreachable!();// because `<Self As PrettyPrinter>::should_print_region` returns false
+// This is reachable (via `pretty_print_dyn_existential`) even though
+// `<Self As PrettyPrinter>::should_print_region` returns false. See #144994.
+Ok(())
 }
 
 fnprint_type(&mutself,ty:Ty<'tcx>) -> Result<(),PrintError>{

compiler/rustc_symbol_mangling/src/legacy.rs

@@ -234,7 +234,9 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
 }
 
 fnprint_region(&mutself,_region: ty::Region<'_>) -> Result<(),PrintError>{
-unreachable!();// because `<Self As PrettyPrinter>::should_print_region` returns false
+// This might be reachable (via `pretty_print_dyn_existential`) even though
+// `<Self As PrettyPrinter>::should_print_region` returns false. See #144994.
+Ok(())
 }
 
 fnprint_type(&mutself,ty:Ty<'tcx>) -> Result<(),PrintError>{

tests/ui/type/type-name-basic.rs

@@ -6,12 +6,85 @@
 #![allow(dead_code)]
 
 use std::any::type_name;
+use std::borrow::Cow;
 
-structFoo<T>{
-x:T,
+structFoo<T>(T);
+
+structBar<'a>(&'au32);
+
+structBaz<'a,T>(&'aT);
+
+traitTrL<'a>{}
+traitTrLA<'a>{
+typeA;
+}
+traitTrLT<'a,T>{}
+traitTrLTA<'a,T>{
+typeA;
+}
+
+macro_rules! t {
+($ty:ty, $str:literal) => {
+ assert_eq!(type_name::<$ty>(), $str);
+}
 }
 
 pubfnmain(){
-assert_eq!(type_name::<isize>(),"isize");
-assert_eq!(type_name::<Foo<usize>>(),"type_name_basic::Foo<usize>");
+t!(bool,"bool");
+t!(char,"char");
+
+t!(u8,"u8");
+t!(u16,"u16");
+t!(u32,"u32");
+t!(u64,"u64");
+t!(u128,"u128");
+t!(usize,"usize");
+
+t!(i8,"i8");
+t!(i16,"i16");
+t!(i32,"i32");
+t!(i64,"i64");
+t!(i128,"i128");
+t!(isize,"isize");
+
+t!(String,"alloc::string::String");
+t!(str,"str");
+t!(&str,"&str");
+t!(&'staticstr,"&str");
+
+t!((u16,u32,u64),"(u16, u32, u64)");
+t!([usize;4],"[usize; 4]");
+t!([usize],"[usize]");
+t!(&[usize],"&[usize]");
+
+t!(*constbool,"*const bool");
+t!(*mutu64,"*mut u64");
+
+t!(Vec<Vec<u32>>,"alloc::vec::Vec<alloc::vec::Vec<u32>>");
+t!(Foo<usize>,"type_name_basic::Foo<usize>");
+t!(Bar<'static>,"type_name_basic::Bar");
+t!(Baz<'static,u32>,"type_name_basic::Baz<u32>");
+
+// FIXME: lifetime omission means these all print badly.
+t!(dyn TrL<'static>,"dyn type_name_basic::TrL<>");
+t!(dyn TrLA<'static,A = u32>,"dyn type_name_basic::TrLA<, A = u32>");
+t!(
+ dyn TrLT<'static,Cow<'static,()>>,
+"dyn type_name_basic::TrLT<, alloc::borrow::Cow<()>>"
+);
+t!(
+ dyn TrLTA<'static,u32,A = Cow<'static,()>>,
+"dyn type_name_basic::TrLTA<, u32, A = alloc::borrow::Cow<()>>"
+);
+
+t!(fn(i32) -> i32,"fn(i32) -> i32");
+t!(dyn for<'a> Fn(&'a u32),"dyn core::ops::function::Fn(&u32)");
+
+structS<'a,T>(&'aT);
+impl<'a,T:Clone>S<'a,T>{
+fntest(){
+t!(Cow<'a,T>,"alloc::borrow::Cow<u32>");
+}
+}
+S::<u32>::test();
 }