Rollup merge of #134081 - oli-obk:push-prpsqxxynxnq, r=BoxyUwU

Try to evaluate constants in legacy mangling

Best reviewed commit by commit.

It seems kind of odd to treat literals differently from unevaluated free constants. So let's evaluate those constants and only fall back to `_` rendering if that fails to result in an integral constant

compiler/rustc_symbol_mangling/src/legacy.rs

@@ -2,7 +2,7 @@ use std::fmt::{self, Write};
 use std::mem::{self, discriminant};
 
 use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
-use rustc_hir::def_id::CrateNum;
+use rustc_hir::def_id::{CrateNum, DefId};
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use rustc_middle::bug;
 use rustc_middle::ty::print::{PrettyPrinter, Print, PrintError, Printer};
@@ -378,6 +378,33 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
             Ok(())
         }
     }
+
+    fn print_impl_path(
+        &mut self,
+        impl_def_id: DefId,
+        args: &'tcx [GenericArg<'tcx>],
+        mut self_ty: Ty<'tcx>,
+        mut impl_trait_ref: Option<ty::TraitRef<'tcx>>,
+    ) -> Result<(), PrintError> {
+        let mut typing_env = ty::TypingEnv::post_analysis(self.tcx, impl_def_id);
+        if !args.is_empty() {
+            typing_env.param_env =
+                ty::EarlyBinder::bind(typing_env.param_env).instantiate(self.tcx, args);
+        }
+
+        match &mut impl_trait_ref {
+            Some(impl_trait_ref) => {
+                assert_eq!(impl_trait_ref.self_ty(), self_ty);
+                *impl_trait_ref = self.tcx.normalize_erasing_regions(typing_env, *impl_trait_ref);
+                self_ty = impl_trait_ref.self_ty();
+            }
+            None => {
+                self_ty = self.tcx.normalize_erasing_regions(typing_env, self_ty);
+            }
+        }
+
+        self.default_print_impl_path(impl_def_id, args, self_ty, impl_trait_ref)
+    }
 }
 
 impl<'tcx> PrettyPrinter<'tcx> for SymbolPrinter<'tcx> {