On E0275 do not print out the full type in the msg

When printing requirement overflow errors, do not print out the full
type name when it is longer than 50 characters long.

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -22,6 +22,7 @@ use rustc_errors::{
     MultiSpan, Style,
 };
 use rustc_hir as hir;
+use rustc_hir::def::Namespace;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::GenericParam;
@@ -34,6 +35,7 @@ use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::ExpectedFound;
 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
+use rustc_middle::ty::print::{FmtPrinter, Print};
 use rustc_middle::ty::{
     self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
     TypeVisitable,
@@ -109,7 +111,10 @@ pub trait TypeErrCtxtExt<'tcx> {
         suggest_increasing_limit: bool,
     ) -> !
     where
-        T: fmt::Display + TypeFoldable<'tcx>;
+        T: fmt::Display
+            + TypeFoldable<'tcx>
+            + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
+        <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug;
 
     fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
 
@@ -468,15 +473,31 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         suggest_increasing_limit: bool,
     ) -> !
     where
-        T: fmt::Display + TypeFoldable<'tcx>,
+        T: fmt::Display
+            + TypeFoldable<'tcx>
+            + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
+        <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
     {
         let predicate = self.resolve_vars_if_possible(obligation.predicate.clone());
+        let mut pred_str = predicate.to_string();
+        if pred_str.len() > 50 {
+            // We don't need to save the type to a file, we will be talking about this type already
+            // in a separate note when we explain the obligation, so it will be available that way.
+            pred_str = predicate
+                .print(FmtPrinter::new_with_limit(
+                    self.tcx,
+                    Namespace::TypeNS,
+                    rustc_session::Limit(6),
+                ))
+                .unwrap()
+                .into_buffer();
+        }
         let mut err = struct_span_err!(
             self.tcx.sess,
             obligation.cause.span,
             E0275,
             "overflow evaluating the requirement `{}`",
-            predicate
+            pred_str,
         );
 
         if suggest_increasing_limit {

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -42,6 +42,7 @@ use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::fold::BottomUpFolder;
+use rustc_middle::ty::print::{FmtPrinter, Print};
 use rustc_middle::ty::relate::TypeRelation;
 use rustc_middle::ty::SubstsRef;
 use rustc_middle::ty::{self, EarlyBinder, PolyProjectionPredicate, ToPolyTraitRef, ToPredicate};
@@ -1081,11 +1082,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         it.for_each(|o| o.recursion_depth = cmp::max(min_depth, o.recursion_depth) + 1);
     }
 
-    fn check_recursion_depth<T: Display + TypeFoldable<'tcx>>(
+    fn check_recursion_depth<T>(
         &self,
         depth: usize,
         error_obligation: &Obligation<'tcx, T>,
-    ) -> Result<(), OverflowError> {
+    ) -> Result<(), OverflowError>
+    where
+        T: fmt::Display
+            + TypeFoldable<'tcx>
+            + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
+        <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
+    {
         if !self.infcx.tcx.recursion_limit().value_within_limit(depth) {
             match self.query_mode {
                 TraitQueryMode::Standard => {
@@ -1109,11 +1116,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// The weird return type of this function allows it to be used with the `try` (`?`)
     /// operator within certain functions.
     #[inline(always)]
-    fn check_recursion_limit<T: Display + TypeFoldable<'tcx>, V: Display + TypeFoldable<'tcx>>(
+    fn check_recursion_limit<T: Display + TypeFoldable<'tcx>, V>(
         &self,
         obligation: &Obligation<'tcx, T>,
         error_obligation: &Obligation<'tcx, V>,
-    ) -> Result<(), OverflowError> {
+    ) -> Result<(), OverflowError>
+    where
+        V: fmt::Display
+            + TypeFoldable<'tcx>
+            + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
+        <V as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
+    {
         self.check_recursion_depth(obligation.recursion_depth, error_obligation)
     }