Allow static regions in type_name.

Fixes #146249.

Author: nnethercote

compiler/rustc_const_eval/src/util/type_name.rs

@@ -17,11 +17,16 @@ impl<'tcx> Printer<'tcx> for TypeNamePrinter<'tcx> {
         self.tcx
     }
 
-    fn print_region(&mut self, _region: ty::Region<'_>) -> Result<(), PrintError> {
+    fn print_region(&mut self, region: ty::Region<'_>) -> Result<(), PrintError> {
         // 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, "'_")
+        // Printing `'_` for non-static regions is a bit hacky but gives mostly
+        // good results, and doing better is difficult. See
+        // `should_print_optional_region`.
+        let s = match region.kind() {
+            ty::ReStatic => "'static",
+            _ => "'_",
+        };
+        write!(self, "{}", s)
     }
 
     fn print_type(&mut self, ty: Ty<'tcx>) -> Result<(), PrintError> {
@@ -168,10 +173,11 @@ impl<'tcx> PrettyPrinter<'tcx> for TypeNamePrinter<'tcx> {
         // 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)".
+        let kind = region.kind();
         match region.kind() {
             ty::ReErased | ty::ReEarlyParam(_) => false,
-            ty::ReBound(..) => true,
-            _ => unreachable!(),
+            ty::ReBound(..) | ty::ReStatic => true,
+            _ => panic!("type_name unhandled region: {kind:?}"),
         }
     }
 

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

@@ -107,4 +107,19 @@ pub fn main() {
     }
     let a = Wrap(&()).get();
     v!(a, "type_name_basic::main::Wrap<&()>::get::Info");
+
+    struct Issue146249<T>(T);
+    impl Issue146249<Box<dyn FnOnce()>> {
+        pub fn bar(&self) {
+            let f = || {};
+            v!(
+                f,
+                "type_name_basic::main::Issue146249<\
+                    alloc::boxed::Box<(dyn core::ops::function::FnOnce() + 'static)>\
+                >::bar::{{closure}}"
+            );
+        }
+    }
+    let v: Issue146249<Box<dyn FnOnce()>> = Issue146249(Box::new(|| {}));
+    v.bar();
 }