Auto merge of #145284 - nnethercote:type_name-print-regions, r=lcnr

Print regions in `type_name`.

Currently they are skipped, which is a bit weird, and it sometimes causes malformed output like `Foo<>` and `dyn Bar<, A = u32>`.

Most regions are erased by the time `type_name` does its work. So all regions are now printed as `'_` in non-optional places. Not perfect, but better than the status quo.

`c_name` is updated to trim lifetimes from MIR pass names, so that the `PASS_NAMES` sanity check still works. It is also renamed as `simplify_pass_type_name` and made non-const, because it doesn't need to be const and the non-const implementation is much shorter.

The commit also renames `should_print_region` as `should_print_optional_region`, which makes it clearer that it only applies to some regions.

Fixes rust-lang/rust#145168.

r? `@lcnr`

1 files changed, 16 insertions, 10 deletions

diff --git a/compiler/rustc_const_eval/src/util/type_name.rs b/compiler/rustc_const_eval/src/util/type_name.rs
index 9d6674873b1..13cc607135a 100644
--- a/compiler/rustc_const_eval/src/util/type_name.rs
+++ b/compiler/rustc_const_eval/src/util/type_name.rs
@@ -5,7 +5,7 @@ use rustc_hir::def_id::CrateNum;
 use rustc_hir::definitions::DisambiguatedDefPathData;
 use rustc_middle::bug;
 use rustc_middle::ty::print::{PrettyPrinter, PrintError, Printer};
-use rustc_middle::ty::{self, GenericArg, GenericArgKind, Ty, TyCtxt};
+use rustc_middle::ty::{self, GenericArg, Ty, TyCtxt};
 
 struct TypeNamePrinter<'tcx> {
     tcx: TyCtxt<'tcx>,
@@ -18,9 +18,10 @@ impl<'tcx> Printer<'tcx> for TypeNamePrinter<'tcx> {
     }
 
     fn print_region(&mut self, _region: ty::Region<'_>) -> Result<(), PrintError> {
-        // This is reachable (via `pretty_print_dyn_existential`) even though
-        // `<Self As PrettyPrinter>::should_print_region` returns false. See #144994.
-        Ok(())
+        // FIXME: most regions have been erased by the time this code runs.
+        // Just printing `'_` is a bit hacky but gives mostly good results, and
+        // doing better is difficult. See `should_print_optional_region`.
+        write!(self, "'_")
     }
 
     fn print_type(&mut self, ty: Ty<'tcx>) -> Result<(), PrintError> {
@@ -125,10 +126,8 @@ impl<'tcx> Printer<'tcx> for TypeNamePrinter<'tcx> {
         args: &[GenericArg<'tcx>],
     ) -> Result<(), PrintError> {
         print_prefix(self)?;
-        let args =
-            args.iter().cloned().filter(|arg| !matches!(arg.kind(), GenericArgKind::Lifetime(_)));
-        if args.clone().next().is_some() {
-            self.generic_delimiters(|cx| cx.comma_sep(args))
+        if !args.is_empty() {
+            self.generic_delimiters(|cx| cx.comma_sep(args.iter().copied()))
         } else {
             Ok(())
         }
@@ -136,8 +135,15 @@ impl<'tcx> Printer<'tcx> for TypeNamePrinter<'tcx> {
 }
 
 impl<'tcx> PrettyPrinter<'tcx> for TypeNamePrinter<'tcx> {
-    fn should_print_region(&self, _region: ty::Region<'_>) -> bool {
-        false
+    fn should_print_optional_region(&self, _region: ty::Region<'_>) -> bool {
+        // Bound regions are always printed (as `'_`), which gives some idea that they are special,
+        // even though the `for` is omitted by the pretty printer.
+        // E.g. `for<'a, 'b> fn(&'a u32, &'b u32)` is printed as "fn(&'_ u32, &'_ u32)".
+        match _region.kind() {
+            ty::ReErased => false,
+            ty::ReBound(..) => true,
+            _ => unreachable!(),
+        }
     }
 
     fn generic_delimiters(