From 6038888118d88ed4175ccb49e9e429865432f253 Mon Sep 17 00:00:00 2001
From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
Date: Mon, 16 Oct 2023 20:46:24 +0200
Subject: [PATCH] Remove `Printer::Error`

It's always a `fmt::Error` except in some cases where it was `!`, but
we're not really winning anything in that case.
---
 .../rustc_const_eval/src/util/type_name.rs    |  36 +++--
 .../src/infer/error_reporting/mod.rs          |  44 +++---
 compiler/rustc_lint/src/context.rs            |  28 ++--
 compiler/rustc_middle/src/ty/print/mod.rs     |  54 +++----
 compiler/rustc_middle/src/ty/print/pretty.rs  | 134 +++++++++---------
 compiler/rustc_symbol_mangling/src/legacy.rs  |  36 +++--
 compiler/rustc_symbol_mangling/src/v0.rs      |  42 +++---
 7 files changed, 180 insertions(+), 194 deletions(-)

diff --git a/compiler/rustc_const_eval/src/util/type_name.rs b/compiler/rustc_const_eval/src/util/type_name.rs
index fba8121ead0..06944a93d3b 100644
--- a/compiler/rustc_const_eval/src/util/type_name.rs
+++ b/compiler/rustc_const_eval/src/util/type_name.rs
@@ -3,7 +3,7 @@ use rustc_hir::def_id::CrateNum;
 use rustc_hir::definitions::DisambiguatedDefPathData;
 use rustc_middle::ty::{
     self,
-    print::{PrettyPrinter, Print, Printer},
+    print::{PrettyPrinter, Print, PrintError, Printer},
     GenericArg, GenericArgKind, Ty, TyCtxt,
 };
 use std::fmt::Write;
@@ -14,17 +14,15 @@ struct AbsolutePathPrinter<'tcx> {
 }
 
 impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
-    type Error = std::fmt::Error;
-
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
 
-    fn print_region(self, _region: ty::Region<'_>) -> Result<Self, Self::Error> {
+    fn print_region(self, _region: ty::Region<'_>) -> Result<Self, PrintError> {
         Ok(self)
     }
 
-    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self, Self::Error> {
+    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self, PrintError> {
         match *ty.kind() {
             // Types without identity.
             ty::Bool
@@ -62,18 +60,18 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
         }
     }
 
-    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self, Self::Error> {
+    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self, PrintError> {
         self.pretty_print_const(ct, false)
     }
 
     fn print_dyn_existential(
         self,
         predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.pretty_print_dyn_existential(predicates)
     }
 
-    fn path_crate(mut self, cnum: CrateNum) -> Result<Self, Self::Error> {
+    fn path_crate(mut self, cnum: CrateNum) -> Result<Self, PrintError> {
         self.path.push_str(self.tcx.crate_name(cnum).as_str());
         Ok(self)
     }
@@ -82,17 +80,17 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
         self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.pretty_path_qualified(self_ty, trait_ref)
     }
 
     fn path_append_impl(
         self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         _disambiguated_data: &DisambiguatedDefPathData,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.pretty_path_append_impl(
             |mut cx| {
                 cx = print_prefix(cx)?;
@@ -108,9 +106,9 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
 
     fn path_append(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = print_prefix(self)?;
 
         write!(self.path, "::{}", disambiguated_data.data).unwrap();
@@ -120,9 +118,9 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
 
     fn path_generic_args(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         args: &[GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = print_prefix(self)?;
         let args =
             args.iter().cloned().filter(|arg| !matches!(arg.unpack(), GenericArgKind::Lifetime(_)));
@@ -138,9 +136,9 @@ impl<'tcx> PrettyPrinter<'tcx> for AbsolutePathPrinter<'tcx> {
     fn should_print_region(&self, _region: ty::Region<'_>) -> bool {
         false
     }
-    fn comma_sep<T>(mut self, mut elems: impl Iterator<Item = T>) -> Result<Self, Self::Error>
+    fn comma_sep<T>(mut self, mut elems: impl Iterator<Item = T>) -> Result<Self, PrintError>
     where
-        T: Print<'tcx, Self, Error = Self::Error>,
+        T: Print<'tcx, Self, Error = PrintError>,
     {
         if let Some(first) = elems.next() {
             self = first.print(self)?;
@@ -154,8 +152,8 @@ impl<'tcx> PrettyPrinter<'tcx> for AbsolutePathPrinter<'tcx> {
 
     fn generic_delimiters(
         mut self,
-        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
-    ) -> Result<Self, Self::Error> {
+        f: impl FnOnce(Self) -> Result<Self, PrintError>,
+    ) -> Result<Self, PrintError> {
         write!(self, "<")?;
 
         self = f(self)?;
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 5a3188b02ee..496bb1766a7 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -67,7 +67,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::dep_graph::DepContext;
-use rustc_middle::ty::print::with_forced_trimmed_paths;
+use rustc_middle::ty::print::{with_forced_trimmed_paths, PrintError};
 use rustc_middle::ty::relate::{self, RelateResult, TypeRelation};
 use rustc_middle::ty::{
     self, error::TypeError, IsSuggestable, List, Region, Ty, TyCtxt, TypeFoldable,
@@ -583,35 +583,31 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             segments: Vec<String>,
         }
 
-        struct NonTrivialPath;
-
         impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
-            type Error = NonTrivialPath;
-
             fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
                 self.tcx
             }
 
-            fn print_region(self, _region: ty::Region<'_>) -> Result<Self, Self::Error> {
-                Err(NonTrivialPath)
+            fn print_region(self, _region: ty::Region<'_>) -> Result<Self, PrintError> {
+                Err(fmt::Error)
             }
 
-            fn print_type(self, _ty: Ty<'tcx>) -> Result<Self, Self::Error> {
-                Err(NonTrivialPath)
+            fn print_type(self, _ty: Ty<'tcx>) -> Result<Self, PrintError> {
+                Err(fmt::Error)
             }
 
             fn print_dyn_existential(
                 self,
                 _predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
-            ) -> Result<Self, Self::Error> {
-                Err(NonTrivialPath)
+            ) -> Result<Self, PrintError> {
+                Err(fmt::Error)
             }
 
-            fn print_const(self, _ct: ty::Const<'tcx>) -> Result<Self, Self::Error> {
-                Err(NonTrivialPath)
+            fn print_const(self, _ct: ty::Const<'tcx>) -> Result<Self, PrintError> {
+                Err(fmt::Error)
             }
 
-            fn path_crate(mut self, cnum: CrateNum) -> Result<Self, Self::Error> {
+            fn path_crate(mut self, cnum: CrateNum) -> Result<Self, PrintError> {
                 self.segments = vec![self.tcx.crate_name(cnum).to_string()];
                 Ok(self)
             }
@@ -619,33 +615,33 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 self,
                 _self_ty: Ty<'tcx>,
                 _trait_ref: Option<ty::TraitRef<'tcx>>,
-            ) -> Result<Self, Self::Error> {
-                Err(NonTrivialPath)
+            ) -> Result<Self, PrintError> {
+                Err(fmt::Error)
             }
 
             fn path_append_impl(
                 self,
-                _print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+                _print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
                 _disambiguated_data: &DisambiguatedDefPathData,
                 _self_ty: Ty<'tcx>,
                 _trait_ref: Option<ty::TraitRef<'tcx>>,
-            ) -> Result<Self, Self::Error> {
-                Err(NonTrivialPath)
+            ) -> Result<Self, PrintError> {
+                Err(fmt::Error)
             }
             fn path_append(
                 mut self,
-                print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+                print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
                 disambiguated_data: &DisambiguatedDefPathData,
-            ) -> Result<Self, Self::Error> {
+            ) -> Result<Self, PrintError> {
                 self = print_prefix(self)?;
                 self.segments.push(disambiguated_data.to_string());
                 Ok(self)
             }
             fn path_generic_args(
                 self,
-                print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+                print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
                 _args: &[GenericArg<'tcx>],
-            ) -> Result<Self, Self::Error> {
+            ) -> Result<Self, PrintError> {
                 print_prefix(self)
             }
         }
@@ -663,7 +659,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
                 // We compare strings because DefPath can be different
                 // for imported and non-imported crates
-                let same_path = || -> Result<_, NonTrivialPath> {
+                let same_path = || -> Result<_, PrintError> {
                     Ok(self.tcx.def_path_str(did1) == self.tcx.def_path_str(did2)
                         || abs_path(did1)? == abs_path(did2)?)
                 };
diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index af7f2bcf669..1f08db30860 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -31,7 +31,7 @@ use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use rustc_middle::middle::privacy::EffectiveVisibilities;
 use rustc_middle::middle::stability;
 use rustc_middle::ty::layout::{LayoutError, LayoutOfHelpers, TyAndLayout};
-use rustc_middle::ty::print::with_no_trimmed_paths;
+use rustc_middle::ty::print::{with_no_trimmed_paths, PrintError};
 use rustc_middle::ty::{self, print::Printer, GenericArg, RegisteredTools, Ty, TyCtxt};
 use rustc_session::config::ExpectedValues;
 use rustc_session::lint::{BuiltinLintDiagnostics, LintExpectationId};
@@ -1206,32 +1206,30 @@ impl<'tcx> LateContext<'tcx> {
         }
 
         impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
-            type Error = !;
-
             fn tcx(&self) -> TyCtxt<'tcx> {
                 self.tcx
             }
 
-            fn print_region(self, _region: ty::Region<'_>) -> Result<Self, Self::Error> {
+            fn print_region(self, _region: ty::Region<'_>) -> Result<Self, PrintError> {
                 Ok(self)
             }
 
-            fn print_type(self, _ty: Ty<'tcx>) -> Result<Self, Self::Error> {
+            fn print_type(self, _ty: Ty<'tcx>) -> Result<Self, PrintError> {
                 Ok(self)
             }
 
             fn print_dyn_existential(
                 self,
                 _predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
-            ) -> Result<Self, Self::Error> {
+            ) -> Result<Self, PrintError> {
                 Ok(self)
             }
 
-            fn print_const(self, _ct: ty::Const<'tcx>) -> Result<Self, Self::Error> {
+            fn print_const(self, _ct: ty::Const<'tcx>) -> Result<Self, PrintError> {
                 Ok(self)
             }
 
-            fn path_crate(mut self, cnum: CrateNum) -> Result<Self, Self::Error> {
+            fn path_crate(mut self, cnum: CrateNum) -> Result<Self, PrintError> {
                 self.path = vec![self.tcx.crate_name(cnum)];
                 Ok(self)
             }
@@ -1240,7 +1238,7 @@ impl<'tcx> LateContext<'tcx> {
                 mut self,
                 self_ty: Ty<'tcx>,
                 trait_ref: Option<ty::TraitRef<'tcx>>,
-            ) -> Result<Self, Self::Error> {
+            ) -> Result<Self, PrintError> {
                 if trait_ref.is_none() {
                     if let ty::Adt(def, args) = self_ty.kind() {
                         return self.print_def_path(def.did(), args);
@@ -1259,11 +1257,11 @@ impl<'tcx> LateContext<'tcx> {
 
             fn path_append_impl(
                 self,
-                print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+                print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
                 _disambiguated_data: &DisambiguatedDefPathData,
                 self_ty: Ty<'tcx>,
                 trait_ref: Option<ty::TraitRef<'tcx>>,
-            ) -> Result<Self, Self::Error> {
+            ) -> Result<Self, PrintError> {
                 let mut path = print_prefix(self)?;
 
                 // This shouldn't ever be needed, but just in case:
@@ -1285,9 +1283,9 @@ impl<'tcx> LateContext<'tcx> {
 
             fn path_append(
                 self,
-                print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+                print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
                 disambiguated_data: &DisambiguatedDefPathData,
-            ) -> Result<Self, Self::Error> {
+            ) -> Result<Self, PrintError> {
                 let mut path = print_prefix(self)?;
 
                 // Skip `::{{extern}}` blocks and `::{{constructor}}` on tuple/unit structs.
@@ -1301,9 +1299,9 @@ impl<'tcx> LateContext<'tcx> {
 
             fn path_generic_args(
                 self,
-                print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+                print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
                 _args: &[GenericArg<'tcx>],
-            ) -> Result<Self, Self::Error> {
+            ) -> Result<Self, PrintError> {
                 print_prefix(self)
             }
         }
diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
index e789374fdd6..a1384c1616f 100644
--- a/compiler/rustc_middle/src/ty/print/mod.rs
+++ b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -10,12 +10,14 @@ use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 mod pretty;
 pub use self::pretty::*;
 
+pub type PrintError = std::fmt::Error;
+
 // FIXME(eddyb) false positive, the lifetime parameters are used with `P:  Printer<...>`.
 #[allow(unused_lifetimes)]
 pub trait Print<'tcx, P> {
     type Error;
 
-    fn print(&self, cx: P) -> Result<P, Self::Error>;
+    fn print(&self, cx: P) -> Result<P, PrintError>;
 }
 
 /// Interface for outputting user-facing "type-system entities"
@@ -28,15 +30,13 @@ pub trait Print<'tcx, P> {
 //
 // FIXME(eddyb) find a better name; this is more general than "printing".
 pub trait Printer<'tcx>: Sized {
-    type Error;
-
     fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
 
     fn print_def_path(
         self,
         def_id: DefId,
         args: &'tcx [GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.default_print_def_path(def_id, args)
     }
 
@@ -46,48 +46,48 @@ pub trait Printer<'tcx>: Sized {
         args: &'tcx [GenericArg<'tcx>],
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.default_print_impl_path(impl_def_id, args, self_ty, trait_ref)
     }
 
-    fn print_region(self, region: ty::Region<'tcx>) -> Result<Self, Self::Error>;
+    fn print_region(self, region: ty::Region<'tcx>) -> Result<Self, PrintError>;
 
-    fn print_type(self, ty: Ty<'tcx>) -> Result<Self, Self::Error>;
+    fn print_type(self, ty: Ty<'tcx>) -> Result<Self, PrintError>;
 
     fn print_dyn_existential(
         self,
         predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
-    ) -> Result<Self, Self::Error>;
+    ) -> Result<Self, PrintError>;
 
-    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self, Self::Error>;
+    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self, PrintError>;
 
-    fn path_crate(self, cnum: CrateNum) -> Result<Self, Self::Error>;
+    fn path_crate(self, cnum: CrateNum) -> Result<Self, PrintError>;
 
     fn path_qualified(
         self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error>;
+    ) -> Result<Self, PrintError>;
 
     fn path_append_impl(
         self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error>;
+    ) -> Result<Self, PrintError>;
 
     fn path_append(
         self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
-    ) -> Result<Self, Self::Error>;
+    ) -> Result<Self, PrintError>;
 
     fn path_generic_args(
         self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         args: &[GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error>;
+    ) -> Result<Self, PrintError>;
 
     // Defaults (should not be overridden):
 
@@ -96,7 +96,7 @@ pub trait Printer<'tcx>: Sized {
         self,
         def_id: DefId,
         args: &'tcx [GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let key = self.tcx().def_key(def_id);
         debug!(?key);
 
@@ -187,7 +187,7 @@ pub trait Printer<'tcx>: Sized {
         _args: &'tcx [GenericArg<'tcx>],
         self_ty: Ty<'tcx>,
         impl_trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         debug!(
             "default_print_impl_path: impl_def_id={:?}, self_ty={}, impl_trait_ref={:?}",
             impl_def_id, self_ty, impl_trait_ref
@@ -288,30 +288,30 @@ pub fn characteristic_def_id_of_type(ty: Ty<'_>) -> Option<DefId> {
 }
 
 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for ty::Region<'tcx> {
-    type Error = P::Error;
-    fn print(&self, cx: P) -> Result<P, Self::Error> {
+    type Error = PrintError;
+    fn print(&self, cx: P) -> Result<P, PrintError> {
         cx.print_region(*self)
     }
 }
 
 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for Ty<'tcx> {
-    type Error = P::Error;
+    type Error = PrintError;
 
-    fn print(&self, cx: P) -> Result<P, Self::Error> {
+    fn print(&self, cx: P) -> Result<P, PrintError> {
         cx.print_type(*self)
     }
 }
 
 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> {
-    type Error = P::Error;
-    fn print(&self, cx: P) -> Result<P, Self::Error> {
+    type Error = PrintError;
+    fn print(&self, cx: P) -> Result<P, PrintError> {
         cx.print_dyn_existential(self)
     }
 }
 
 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for ty::Const<'tcx> {
-    type Error = P::Error;
-    fn print(&self, cx: P) -> Result<P, Self::Error> {
+    type Error = PrintError;
+    fn print(&self, cx: P) -> Result<P, PrintError> {
         cx.print_const(*self)
     }
 }
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index ae3e6885b75..f1b17ddd230 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -205,19 +205,19 @@ impl<'tcx> RegionHighlightMode<'tcx> {
 }
 
 /// Trait for printers that pretty-print using `fmt::Write` to the printer.
-pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
+pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
     /// Like `print_def_path` but for value paths.
     fn print_value_path(
         self,
         def_id: DefId,
         args: &'tcx [GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.print_def_path(def_id, args)
     }
 
-    fn in_binder<T>(self, value: &ty::Binder<'tcx, T>) -> Result<Self, Self::Error>
+    fn in_binder<T>(self, value: &ty::Binder<'tcx, T>) -> Result<Self, PrintError>
     where
-        T: Print<'tcx, Self, Error = Self::Error> + TypeFoldable<TyCtxt<'tcx>>,
+        T: Print<'tcx, Self, Error = PrintError> + TypeFoldable<TyCtxt<'tcx>>,
     {
         value.as_ref().skip_binder().print(self)
     }
@@ -226,17 +226,17 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         self,
         value: &ty::Binder<'tcx, T>,
         f: F,
-    ) -> Result<Self, Self::Error>
+    ) -> Result<Self, PrintError>
     where
-        T: Print<'tcx, Self, Error = Self::Error> + TypeFoldable<TyCtxt<'tcx>>,
+        T: Print<'tcx, Self, Error = PrintError> + TypeFoldable<TyCtxt<'tcx>>,
     {
         f(value.as_ref().skip_binder(), self)
     }
 
     /// Prints comma-separated elements.
-    fn comma_sep<T>(mut self, mut elems: impl Iterator<Item = T>) -> Result<Self, Self::Error>
+    fn comma_sep<T>(mut self, mut elems: impl Iterator<Item = T>) -> Result<Self, PrintError>
     where
-        T: Print<'tcx, Self, Error = Self::Error>,
+        T: Print<'tcx, Self, Error = PrintError>,
     {
         if let Some(first) = elems.next() {
             self = first.print(self)?;
@@ -251,10 +251,10 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
     /// Prints `{f: t}` or `{f as t}` depending on the `cast` argument
     fn typed_value(
         mut self,
-        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
-        t: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        f: impl FnOnce(Self) -> Result<Self, PrintError>,
+        t: impl FnOnce(Self) -> Result<Self, PrintError>,
         conversion: &str,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.write_str("{")?;
         self = f(self)?;
         self.write_str(conversion)?;
@@ -266,8 +266,8 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
     /// Prints `<...>` around what `f` prints.
     fn generic_delimiters(
         self,
-        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
-    ) -> Result<Self, Self::Error>;
+        f: impl FnOnce(Self) -> Result<Self, PrintError>,
+    ) -> Result<Self, PrintError>;
 
     /// Returns `true` if the region should be printed in
     /// optional positions, e.g., `&'a T` or `dyn Tr + 'b`.
@@ -281,7 +281,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
     /// If possible, this returns a global path resolving to `def_id` that is visible
     /// from at least one local module, and returns `true`. If the crate defining `def_id` is
     /// declared with an `extern crate`, the path is guaranteed to use the `extern crate`.
-    fn try_print_visible_def_path(self, def_id: DefId) -> Result<(Self, bool), Self::Error> {
+    fn try_print_visible_def_path(self, def_id: DefId) -> Result<(Self, bool), PrintError> {
         if NO_VISIBLE_PATH.with(|flag| flag.get()) {
             return Ok((self, false));
         }
@@ -295,7 +295,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
     // For enum variants, if they have an unique name, then we only print the name, otherwise we
     // print the enum name and the variant name. Otherwise, we do not print anything and let the
     // caller use the `print_def_path` fallback.
-    fn force_print_trimmed_def_path(mut self, def_id: DefId) -> Result<(Self, bool), Self::Error> {
+    fn force_print_trimmed_def_path(mut self, def_id: DefId) -> Result<(Self, bool), PrintError> {
         let key = self.tcx().def_key(def_id);
         let visible_parent_map = self.tcx().visible_parent_map(());
         let kind = self.tcx().def_kind(def_id);
@@ -365,7 +365,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
     }
 
     /// Try to see if this path can be trimmed to a unique symbol name.
-    fn try_print_trimmed_def_path(mut self, def_id: DefId) -> Result<(Self, bool), Self::Error> {
+    fn try_print_trimmed_def_path(mut self, def_id: DefId) -> Result<(Self, bool), PrintError> {
         if FORCE_TRIMMED_PATH.with(|flag| flag.get()) {
             let (s, trimmed) = self.force_print_trimmed_def_path(def_id)?;
             if trimmed {
@@ -407,7 +407,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         mut self,
         def_id: DefId,
         callers: &mut Vec<DefId>,
-    ) -> Result<(Self, bool), Self::Error> {
+    ) -> Result<(Self, bool), PrintError> {
         define_scoped_cx!(self);
 
         debug!("try_print_visible_def_path: def_id={:?}", def_id);
@@ -579,7 +579,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         if trait_ref.is_none() {
             // Inherent impls. Try to print `Foo::bar` for an inherent
             // impl on `Foo`, but fallback to `<Foo>::bar` if self-type is
@@ -613,10 +613,10 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
 
     fn pretty_path_append_impl(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = print_prefix(self)?;
 
         self.generic_delimiters(|mut cx| {
@@ -632,7 +632,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         })
     }
 
-    fn pretty_print_type(mut self, ty: Ty<'tcx>) -> Result<Self, Self::Error> {
+    fn pretty_print_type(mut self, ty: Ty<'tcx>) -> Result<Self, PrintError> {
         define_scoped_cx!(self);
 
         match *ty.kind() {
@@ -903,7 +903,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         mut self,
         def_id: DefId,
         args: &'tcx ty::List<ty::GenericArg<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let tcx = self.tcx();
 
         // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,
@@ -1173,7 +1173,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
     fn pretty_print_inherent_projection(
         self,
         alias_ty: &ty::AliasTy<'tcx>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let def_key = self.tcx().def_key(alias_ty.def_id);
         self.path_generic_args(
             |cx| {
@@ -1197,7 +1197,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
     fn pretty_print_dyn_existential(
         mut self,
         predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         // Generate the main trait ref, including associated types.
         let mut first = true;
 
@@ -1290,7 +1290,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         inputs: &[Ty<'tcx>],
         c_variadic: bool,
         output: Ty<'tcx>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         define_scoped_cx!(self);
 
         p!("(", comma_sep(inputs.iter().copied()));
@@ -1312,7 +1312,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         mut self,
         ct: ty::Const<'tcx>,
         print_ty: bool,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         define_scoped_cx!(self);
 
         if self.should_print_verbose() {
@@ -1388,7 +1388,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         Ok(self)
     }
 
-    fn pretty_print_const_scalar(self, scalar: Scalar, ty: Ty<'tcx>) -> Result<Self, Self::Error> {
+    fn pretty_print_const_scalar(self, scalar: Scalar, ty: Ty<'tcx>) -> Result<Self, PrintError> {
         match scalar {
             Scalar::Ptr(ptr, _size) => self.pretty_print_const_scalar_ptr(ptr, ty),
             Scalar::Int(int) => {
@@ -1401,7 +1401,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         mut self,
         ptr: Pointer,
         ty: Ty<'tcx>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         define_scoped_cx!(self);
 
         let (alloc_id, offset) = ptr.into_parts();
@@ -1463,7 +1463,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         int: ScalarInt,
         ty: Ty<'tcx>,
         print_ty: bool,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         define_scoped_cx!(self);
 
         match ty.kind() {
@@ -1525,7 +1525,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         self,
         _: Pointer<Prov>,
         ty: Ty<'tcx>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.typed_value(
             |mut this| {
                 this.write_str("&_")?;
@@ -1536,7 +1536,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         )
     }
 
-    fn pretty_print_byte_str(mut self, byte_str: &'tcx [u8]) -> Result<Self, Self::Error> {
+    fn pretty_print_byte_str(mut self, byte_str: &'tcx [u8]) -> Result<Self, PrintError> {
         write!(self, "b\"{}\"", byte_str.escape_ascii())?;
         Ok(self)
     }
@@ -1546,7 +1546,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
         valtree: ty::ValTree<'tcx>,
         ty: Ty<'tcx>,
         print_ty: bool,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         define_scoped_cx!(self);
 
         if self.should_print_verbose() {
@@ -1669,7 +1669,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx, Error = fmt::Error> + fmt::Write {
     fn pretty_closure_as_impl(
         mut self,
         closure: ty::ClosureArgs<'tcx>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let sig = closure.sig();
         let kind = closure.kind_ty().to_opt_closure_kind().unwrap_or(ty::ClosureKind::Fn);
 
@@ -1842,8 +1842,6 @@ impl fmt::Write for FmtPrinter<'_, '_> {
 }
 
 impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
-    type Error = fmt::Error;
-
     fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
         self.tcx
     }
@@ -1852,7 +1850,7 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         mut self,
         def_id: DefId,
         args: &'tcx [GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         define_scoped_cx!(self);
 
         if args.is_empty() {
@@ -1907,11 +1905,11 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         self.default_print_def_path(def_id, args)
     }
 
-    fn print_region(self, region: ty::Region<'tcx>) -> Result<Self, Self::Error> {
+    fn print_region(self, region: ty::Region<'tcx>) -> Result<Self, PrintError> {
         self.pretty_print_region(region)
     }
 
-    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self, Self::Error> {
+    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self, PrintError> {
         if self.type_length_limit.value_within_limit(self.printed_type_count) {
             self.printed_type_count += 1;
             self.pretty_print_type(ty)
@@ -1925,15 +1923,15 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
     fn print_dyn_existential(
         self,
         predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.pretty_print_dyn_existential(predicates)
     }
 
-    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self, Self::Error> {
+    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self, PrintError> {
         self.pretty_print_const(ct, false)
     }
 
-    fn path_crate(mut self, cnum: CrateNum) -> Result<Self, Self::Error> {
+    fn path_crate(mut self, cnum: CrateNum) -> Result<Self, PrintError> {
         self.empty_path = true;
         if cnum == LOCAL_CRATE {
             if self.tcx.sess.at_least_rust_2018() {
@@ -1954,7 +1952,7 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         mut self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = self.pretty_path_qualified(self_ty, trait_ref)?;
         self.empty_path = false;
         Ok(self)
@@ -1962,11 +1960,11 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
 
     fn path_append_impl(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         _disambiguated_data: &DisambiguatedDefPathData,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = self.pretty_path_append_impl(
             |mut cx| {
                 cx = print_prefix(cx)?;
@@ -1985,9 +1983,9 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
 
     fn path_append(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = print_prefix(self)?;
 
         // Skip `::{{extern}}` blocks and `::{{constructor}}` on tuple/unit structs.
@@ -2016,9 +2014,9 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
 
     fn path_generic_args(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         args: &[GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = print_prefix(self)?;
 
         let tcx = self.tcx;
@@ -2075,7 +2073,7 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
         mut self,
         def_id: DefId,
         args: &'tcx [GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let was_in_value = std::mem::replace(&mut self.in_value, true);
         self = self.print_def_path(def_id, args)?;
         self.in_value = was_in_value;
@@ -2083,30 +2081,30 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
         Ok(self)
     }
 
-    fn in_binder<T>(self, value: &ty::Binder<'tcx, T>) -> Result<Self, Self::Error>
+    fn in_binder<T>(self, value: &ty::Binder<'tcx, T>) -> Result<Self, PrintError>
     where
-        T: Print<'tcx, Self, Error = Self::Error> + TypeFoldable<TyCtxt<'tcx>>,
+        T: Print<'tcx, Self, Error = PrintError> + TypeFoldable<TyCtxt<'tcx>>,
     {
         self.pretty_in_binder(value)
     }
 
-    fn wrap_binder<T, C: FnOnce(&T, Self) -> Result<Self, Self::Error>>(
+    fn wrap_binder<T, C: FnOnce(&T, Self) -> Result<Self, PrintError>>(
         self,
         value: &ty::Binder<'tcx, T>,
         f: C,
-    ) -> Result<Self, Self::Error>
+    ) -> Result<Self, PrintError>
     where
-        T: Print<'tcx, Self, Error = Self::Error> + TypeFoldable<TyCtxt<'tcx>>,
+        T: Print<'tcx, Self, Error = PrintError> + TypeFoldable<TyCtxt<'tcx>>,
     {
         self.pretty_wrap_binder(value, f)
     }
 
     fn typed_value(
         mut self,
-        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
-        t: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        f: impl FnOnce(Self) -> Result<Self, PrintError>,
+        t: impl FnOnce(Self) -> Result<Self, PrintError>,
         conversion: &str,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.write_str("{")?;
         self = f(self)?;
         self.write_str(conversion)?;
@@ -2119,8 +2117,8 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
 
     fn generic_delimiters(
         mut self,
-        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
-    ) -> Result<Self, Self::Error> {
+        f: impl FnOnce(Self) -> Result<Self, PrintError>,
+    ) -> Result<Self, PrintError> {
         write!(self, "<")?;
 
         let was_in_value = std::mem::replace(&mut self.in_value, false);
@@ -2180,7 +2178,7 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
         self,
         p: Pointer<Prov>,
         ty: Ty<'tcx>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let print = |mut this: Self| {
             define_scoped_cx!(this);
             if this.print_alloc_ids {
@@ -2596,22 +2594,22 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
 
 impl<'tcx, T, P: PrettyPrinter<'tcx>> Print<'tcx, P> for ty::Binder<'tcx, T>
 where
-    T: Print<'tcx, P, Error = P::Error> + TypeFoldable<TyCtxt<'tcx>>,
+    T: Print<'tcx, P, Error = PrintError> + TypeFoldable<TyCtxt<'tcx>>,
 {
-    type Error = P::Error;
+    type Error = PrintError;
 
-    fn print(&self, cx: P) -> Result<P, Self::Error> {
+    fn print(&self, cx: P) -> Result<P, PrintError> {
         cx.in_binder(self)
     }
 }
 
 impl<'tcx, T, U, P: PrettyPrinter<'tcx>> Print<'tcx, P> for ty::OutlivesPredicate<T, U>
 where
-    T: Print<'tcx, P, Error = P::Error>,
-    U: Print<'tcx, P, Error = P::Error>,
+    T: Print<'tcx, P, Error = PrintError>,
+    U: Print<'tcx, P, Error = PrintError>,
 {
-    type Error = P::Error;
-    fn print(&self, mut cx: P) -> Result<P, Self::Error> {
+    type Error = PrintError;
+    fn print(&self, mut cx: P) -> Result<P, PrintError> {
         define_scoped_cx!(cx);
         p!(print(self.0), ": ", print(self.1));
         Ok(cx)
@@ -2639,7 +2637,7 @@ macro_rules! define_print_and_forward_display {
     (($self:ident, $cx:ident): $($ty:ty $print:block)+) => {
         $(impl<'tcx, P: PrettyPrinter<'tcx>> Print<'tcx, P> for $ty {
             type Error = fmt::Error;
-            fn print(&$self, $cx: P) -> Result<P, Self::Error> {
+            fn print(&$self, $cx: P) -> Result<P, PrintError> {
                 #[allow(unused_mut)]
                 let mut $cx = $cx;
                 define_scoped_cx!($cx);
diff --git a/compiler/rustc_symbol_mangling/src/legacy.rs b/compiler/rustc_symbol_mangling/src/legacy.rs
index 9b8646a7751..5e7dba63ff7 100644
--- a/compiler/rustc_symbol_mangling/src/legacy.rs
+++ b/compiler/rustc_symbol_mangling/src/legacy.rs
@@ -1,7 +1,7 @@
 use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
 use rustc_hir::def_id::CrateNum;
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
-use rustc_middle::ty::print::{PrettyPrinter, Print, Printer};
+use rustc_middle::ty::print::{PrettyPrinter, Print, PrintError, Printer};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeVisitableExt};
 use rustc_middle::ty::{GenericArg, GenericArgKind};
 use rustc_middle::util::common::record_time;
@@ -200,17 +200,15 @@ struct SymbolPrinter<'tcx> {
 // symbol names should have their own printing machinery.
 
 impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
-    type Error = fmt::Error;
-
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
 
-    fn print_region(self, _region: ty::Region<'_>) -> Result<Self, Self::Error> {
+    fn print_region(self, _region: ty::Region<'_>) -> Result<Self, PrintError> {
         Ok(self)
     }
 
-    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self, Self::Error> {
+    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self, PrintError> {
         match *ty.kind() {
             // Print all nominal types as paths (unlike `pretty_print_type`).
             ty::FnDef(def_id, args)
@@ -244,7 +242,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
     fn print_dyn_existential(
         mut self,
         predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let mut first = true;
         for p in predicates {
             if !first {
@@ -256,7 +254,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
         Ok(self)
     }
 
-    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self, Self::Error> {
+    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self, PrintError> {
         // only print integers
         match (ct.kind(), ct.ty().kind()) {
             (ty::ConstKind::Value(ty::ValTree::Leaf(scalar)), ty::Int(_) | ty::Uint(_)) => {
@@ -274,7 +272,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
         Ok(self)
     }
 
-    fn path_crate(self, cnum: CrateNum) -> Result<Self, Self::Error> {
+    fn path_crate(self, cnum: CrateNum) -> Result<Self, PrintError> {
         self.write_str(self.tcx.crate_name(cnum).as_str())?;
         Ok(self)
     }
@@ -282,7 +280,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
         self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         // Similar to `pretty_path_qualified`, but for the other
         // types that are printed as paths (see `print_type` above).
         match self_ty.kind() {
@@ -298,11 +296,11 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
 
     fn path_append_impl(
         self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         _disambiguated_data: &DisambiguatedDefPathData,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self.pretty_path_append_impl(
             |mut cx| {
                 cx = print_prefix(cx)?;
@@ -322,9 +320,9 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
     }
     fn path_append(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = print_prefix(self)?;
 
         // Skip `::{{extern}}` blocks and `::{{constructor}}` on tuple/unit structs.
@@ -345,9 +343,9 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
     }
     fn path_generic_args(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         args: &[GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         self = print_prefix(self)?;
 
         let args =
@@ -365,9 +363,9 @@ impl<'tcx> PrettyPrinter<'tcx> for &mut SymbolPrinter<'tcx> {
     fn should_print_region(&self, _region: ty::Region<'_>) -> bool {
         false
     }
-    fn comma_sep<T>(mut self, mut elems: impl Iterator<Item = T>) -> Result<Self, Self::Error>
+    fn comma_sep<T>(mut self, mut elems: impl Iterator<Item = T>) -> Result<Self, PrintError>
     where
-        T: Print<'tcx, Self, Error = Self::Error>,
+        T: Print<'tcx, Self, Error = PrintError>,
     {
         if let Some(first) = elems.next() {
             self = first.print(self)?;
@@ -381,8 +379,8 @@ impl<'tcx> PrettyPrinter<'tcx> for &mut SymbolPrinter<'tcx> {
 
     fn generic_delimiters(
         mut self,
-        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
-    ) -> Result<Self, Self::Error> {
+        f: impl FnOnce(Self) -> Result<Self, PrintError>,
+    ) -> Result<Self, PrintError> {
         write!(self, "<")?;
 
         let kept_within_component = mem::replace(&mut self.keep_within_component, true);
diff --git a/compiler/rustc_symbol_mangling/src/v0.rs b/compiler/rustc_symbol_mangling/src/v0.rs
index 249cdf7bdfa..99c5d016439 100644
--- a/compiler/rustc_symbol_mangling/src/v0.rs
+++ b/compiler/rustc_symbol_mangling/src/v0.rs
@@ -6,7 +6,7 @@ use rustc_hir::def::CtorKind;
 use rustc_hir::def_id::{CrateNum, DefId};
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use rustc_middle::ty::layout::IntegerExt;
-use rustc_middle::ty::print::{Print, Printer};
+use rustc_middle::ty::print::{Print, PrintError, Printer};
 use rustc_middle::ty::{
     self, EarlyBinder, FloatTy, Instance, IntTy, Ty, TyCtxt, TypeVisitable, TypeVisitableExt,
     UintTy,
@@ -181,11 +181,11 @@ impl<'tcx> SymbolMangler<'tcx> {
 
     fn path_append_ns<'a>(
         mut self: &'a mut Self,
-        print_prefix: impl FnOnce(&'a mut Self) -> Result<&'a mut Self, !>,
+        print_prefix: impl FnOnce(&'a mut Self) -> Result<&'a mut Self, PrintError>,
         ns: char,
         disambiguator: u64,
         name: &str,
-    ) -> Result<&'a mut Self, !> {
+    ) -> Result<&'a mut Self, PrintError> {
         self.push("N");
         self.out.push(ns);
         self = print_prefix(self)?;
@@ -194,7 +194,7 @@ impl<'tcx> SymbolMangler<'tcx> {
         Ok(self)
     }
 
-    fn print_backref(&mut self, i: usize) -> Result<&mut Self, !> {
+    fn print_backref(&mut self, i: usize) -> Result<&mut Self, PrintError> {
         self.push("B");
         self.push_integer_62((i - self.start_offset) as u64);
         Ok(self)
@@ -203,8 +203,8 @@ impl<'tcx> SymbolMangler<'tcx> {
     fn in_binder<'a, T>(
         mut self: &'a mut Self,
         value: &ty::Binder<'tcx, T>,
-        print_value: impl FnOnce(&'a mut Self, &T) -> Result<&'a mut Self, !>,
-    ) -> Result<&'a mut Self, !>
+        print_value: impl FnOnce(&'a mut Self, &T) -> Result<&'a mut Self, PrintError>,
+    ) -> Result<&'a mut Self, PrintError>
     where
         T: TypeVisitable<TyCtxt<'tcx>>,
     {
@@ -230,8 +230,6 @@ impl<'tcx> SymbolMangler<'tcx> {
 }
 
 impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
-    type Error = !;
-
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
@@ -240,7 +238,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
         mut self,
         def_id: DefId,
         args: &'tcx [GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         if let Some(&i) = self.paths.get(&(def_id, args)) {
             return self.print_backref(i);
         }
@@ -262,7 +260,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
         args: &'tcx [GenericArg<'tcx>],
         mut self_ty: Ty<'tcx>,
         mut impl_trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let key = self.tcx.def_key(impl_def_id);
         let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };
 
@@ -315,7 +313,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
         Ok(self)
     }
 
-    fn print_region(self, region: ty::Region<'_>) -> Result<Self, Self::Error> {
+    fn print_region(self, region: ty::Region<'_>) -> Result<Self, PrintError> {
         let i = match *region {
             // Erased lifetimes use the index 0, for a
             // shorter mangling of `L_`.
@@ -337,7 +335,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
         Ok(self)
     }
 
-    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self, Self::Error> {
+    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self, PrintError> {
         // Basic types, never cached (single-character).
         let basic_type = match ty.kind() {
             ty::Bool => "b",
@@ -492,7 +490,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
     fn print_dyn_existential(
         mut self,
         predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         // Okay, so this is a bit tricky. Imagine we have a trait object like
         // `dyn for<'a> Foo<'a, Bar = &'a ()>`. When we mangle this, the
         // output looks really close to the syntax, where the `Bar = &'a ()` bit
@@ -553,7 +551,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
         Ok(self)
     }
 
-    fn print_const(mut self, ct: ty::Const<'tcx>) -> Result<Self, Self::Error> {
+    fn print_const(mut self, ct: ty::Const<'tcx>) -> Result<Self, PrintError> {
         // We only mangle a typed value if the const can be evaluated.
         let ct = ct.normalize(self.tcx, ty::ParamEnv::reveal_all());
         match ct.kind() {
@@ -725,7 +723,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
         Ok(self)
     }
 
-    fn path_crate(self, cnum: CrateNum) -> Result<Self, Self::Error> {
+    fn path_crate(self, cnum: CrateNum) -> Result<Self, PrintError> {
         self.push("C");
         let stable_crate_id = self.tcx.def_path_hash(cnum.as_def_id()).stable_crate_id();
         self.push_disambiguator(stable_crate_id.as_u64());
@@ -738,7 +736,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
         mut self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         assert!(trait_ref.is_some());
         let trait_ref = trait_ref.unwrap();
 
@@ -749,20 +747,20 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
 
     fn path_append_impl(
         self,
-        _: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        _: impl FnOnce(Self) -> Result<Self, PrintError>,
         _: &DisambiguatedDefPathData,
         _: Ty<'tcx>,
         _: Option<ty::TraitRef<'tcx>>,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         // Inlined into `print_impl_path`
         unreachable!()
     }
 
     fn path_append(
         self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         let ns = match disambiguated_data.data {
             // Extern block segments can be skipped, names from extern blocks
             // are effectively living in their parent modules.
@@ -800,9 +798,9 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
 
     fn path_generic_args(
         mut self,
-        print_prefix: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        print_prefix: impl FnOnce(Self) -> Result<Self, PrintError>,
         args: &[GenericArg<'tcx>],
-    ) -> Result<Self, Self::Error> {
+    ) -> Result<Self, PrintError> {
         // Don't print any regions if they're all erased.
         let print_regions = args.iter().any(|arg| match arg.unpack() {
             GenericArgKind::Lifetime(r) => !r.is_erased(),