rust-lang · estebank · Jul 29, 2025
diff --git a/compiler/rustc_middle/messages.ftl b/compiler/rustc_middle/messages.ftl
@@ -122,8 +122,6 @@ middle_strict_coherence_needs_negative_coherence =
     to use `strict_coherence` on this trait, the `with_negative_coherence` feature must be enabled
     .label = due to this attribute
 
-middle_type_length_limit = reached the type-length limit while instantiating `{$shrunk}`
+middle_type_length_limit = reached the type-length limit while instantiating `{$instance}`
 
 middle_unsupported_union = we don't support unions yet: '{$ty_name}'
-
-middle_written_to_path = the full type name has been written to '{$path}'
diff --git a/compiler/rustc_middle/src/error.rs b/compiler/rustc_middle/src/error.rs
@@ -1,12 +1,12 @@
-use std::path::{Path, PathBuf};
+use std::path::Path;
 use std::{fmt, io};
 
 use rustc_errors::codes::*;
 use rustc_errors::{DiagArgName, DiagArgValue, DiagMessage};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{Span, Symbol};
 
-use crate::ty::Ty;
+use crate::ty::{Instance, Ty};
 
 #[derive(Diagnostic)]
 #[diag(middle_drop_check_overflow, code = E0320)]
@@ -161,13 +161,10 @@ pub(crate) struct ErroneousConstant {
 #[derive(Diagnostic)]
 #[diag(middle_type_length_limit)]
 #[help(middle_consider_type_length_limit)]
-pub(crate) struct TypeLengthLimit {
+pub(crate) struct TypeLengthLimit<'tcx> {
     #[primary_span]
     pub span: Span,
-    pub shrunk: String,
-    #[note(middle_written_to_path)]
-    pub was_written: bool,
-    pub path: PathBuf,
+    pub instance: Instance<'tcx>,
     pub type_length: usize,
 }
 

diff --git a/compiler/rustc_middle/src/ty/diagnostics.rs b/compiler/rustc_middle/src/ty/diagnostics.rs
@@ -7,14 +7,14 @@ use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::{
     Applicability, Diag, DiagArgValue, IntoDiagArg, into_diag_arg_using_display, listify, pluralize,
 };
-use rustc_hir::def::DefKind;
+use rustc_hir::def::{DefKind, Namespace};
 use rustc_hir::def_id::DefId;
 use rustc_hir::{self as hir, AmbigArg, LangItem, PredicateOrigin, WherePredicateKind};
 use rustc_span::{BytePos, Span};
 use rustc_type_ir::TyKind::*;
 
 use crate::ty::{
-    self, AliasTy, Const, ConstKind, FallibleTypeFolder, InferConst, InferTy, Opaque,
+    self, AliasTy, Const, ConstKind, FallibleTypeFolder, InferConst, InferTy, Instance, Opaque,
     PolyTraitPredicate, Projection, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
     TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
@@ -28,6 +28,15 @@ impl IntoDiagArg for Ty<'_> {
     }
 }
 
+impl IntoDiagArg for Instance<'_> {
+    fn into_diag_arg(self, path: &mut Option<std::path::PathBuf>) -> rustc_errors::DiagArgValue {
+        ty::tls::with(|tcx| {
+            let instance = tcx.short_string_namespace(self, path, Namespace::ValueNS);
+            rustc_errors::DiagArgValue::Str(std::borrow::Cow::Owned(instance))
+        })
+    }
+}
+
 into_diag_arg_using_display! {
     ty::Region<'_>,
 }

diff --git a/compiler/rustc_middle/src/ty/error.rs b/compiler/rustc_middle/src/ty/error.rs
@@ -160,7 +160,11 @@ impl<'tcx> Ty<'tcx> {
             _ => {
                 let width = tcx.sess.diagnostic_width();
                 let length_limit = std::cmp::max(width / 4, 40);
-                format!("`{}`", tcx.string_with_limit(self, length_limit)).into()
+                format!(
+                    "`{}`",
+                    tcx.string_with_limit(self, length_limit, hir::def::Namespace::TypeNS)
+                )
+                .into()
             }
         }
     }
@@ -213,12 +217,12 @@ impl<'tcx> Ty<'tcx> {
 }
 
 impl<'tcx> TyCtxt<'tcx> {
-    pub fn string_with_limit<T>(self, p: T, length_limit: usize) -> String
+    pub fn string_with_limit<T>(self, p: T, length_limit: usize, ns: hir::def::Namespace) -> String
     where
         T: Copy + for<'a, 'b> Lift<TyCtxt<'b>, Lifted: Print<'b, FmtPrinter<'a, 'b>>>,
     {
         let mut type_limit = 50;
-        let regular = FmtPrinter::print_string(self, hir::def::Namespace::TypeNS, |cx| {
+        let regular = FmtPrinter::print_string(self, ns, |cx| {
             self.lift(p).expect("could not lift for printing").print(cx)
         })
         .expect("could not write to `String`");
@@ -229,11 +233,7 @@ impl<'tcx> TyCtxt<'tcx> {
         loop {
             // Look for the longest properly trimmed path that still fits in length_limit.
             short = with_forced_trimmed_paths!({
-                let mut cx = FmtPrinter::new_with_limit(
-                    self,
-                    hir::def::Namespace::TypeNS,
-                    rustc_session::Limit(type_limit),
-                );
+                let mut cx = FmtPrinter::new_with_limit(self, ns, rustc_session::Limit(type_limit));
                 self.lift(p)
                     .expect("could not lift for printing")
                     .print(&mut cx)
@@ -251,12 +251,28 @@ impl<'tcx> TyCtxt<'tcx> {
     /// When calling this after a `Diag` is constructed, the preferred way of doing so is
     /// `tcx.short_string(ty, diag.long_ty_path())`. The diagnostic itself is the one that keeps
     /// the existence of a "long type" anywhere in the diagnostic, so the note telling the user
-    /// where we wrote the file to is only printed once.
+    /// where we wrote the file to is only printed once. The path will use the type namespace.
     pub fn short_string<T>(self, p: T, path: &mut Option<PathBuf>) -> String
     where
         T: Copy + Hash + for<'a, 'b> Lift<TyCtxt<'b>, Lifted: Print<'b, FmtPrinter<'a, 'b>>>,
     {
-        let regular = FmtPrinter::print_string(self, hir::def::Namespace::TypeNS, |cx| {
+        self.short_string_namespace(p, path, hir::def::Namespace::TypeNS)
+    }
+
+    /// When calling this after a `Diag` is constructed, the preferred way of doing so is
+    /// `tcx.short_string(ty, diag.long_ty_path())`. The diagnostic itself is the one that keeps
+    /// the existence of a "long type" anywhere in the diagnostic, so the note telling the user
+    /// where we wrote the file to is only printed once.
+    pub fn short_string_namespace<T>(
+        self,
+        p: T,
+        path: &mut Option<PathBuf>,
+        namespace: hir::def::Namespace,
+    ) -> String
+    where
+        T: Copy + Hash + for<'a, 'b> Lift<TyCtxt<'b>, Lifted: Print<'b, FmtPrinter<'a, 'b>>>,
+    {
+        let regular = FmtPrinter::print_string(self, namespace, |cx| {
             self.lift(p).expect("could not lift for printing").print(cx)
         })
         .expect("could not write to `String`");
@@ -270,7 +286,7 @@ impl<'tcx> TyCtxt<'tcx> {
         if regular.len() <= width * 2 / 3 {
             return regular;
         }
-        let short = self.string_with_limit(p, length_limit);
+        let short = self.string_with_limit(p, length_limit, namespace);
         if regular == short {
             return regular;
         }

diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs
@@ -1,6 +1,5 @@
 use std::assert_matches::assert_matches;
 use std::fmt;
-use std::path::PathBuf;
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::ErrorGuaranteed;
@@ -17,7 +16,7 @@ use tracing::{debug, instrument};
 use crate::error;
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::ty::normalize_erasing_regions::NormalizationError;
-use crate::ty::print::{FmtPrinter, Printer, shrunk_instance_name};
+use crate::ty::print::{FmtPrinter, Print};
 use crate::ty::{
     self, EarlyBinder, GenericArgs, GenericArgsRef, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
     TypeVisitable, TypeVisitableExt, TypeVisitor,
@@ -389,59 +388,15 @@ fn type_length<'tcx>(item: impl TypeVisitable<TyCtxt<'tcx>>) -> usize {
     visitor.type_length
 }
 
-pub fn fmt_instance(
-    f: &mut fmt::Formatter<'_>,
-    instance: Instance<'_>,
-    type_length: Option<rustc_session::Limit>,
-) -> fmt::Result {
-    ty::tls::with(|tcx| {
-        let args = tcx.lift(instance.args).expect("could not lift for printing");
-
-        let mut cx = if let Some(type_length) = type_length {
-            FmtPrinter::new_with_limit(tcx, Namespace::ValueNS, type_length)
-        } else {
-            FmtPrinter::new(tcx, Namespace::ValueNS)
-        };
-        cx.print_def_path(instance.def_id(), args)?;
-        let s = cx.into_buffer();
-        f.write_str(&s)
-    })?;
-
-    match instance.def {
-        InstanceKind::Item(_) => Ok(()),
-        InstanceKind::VTableShim(_) => write!(f, " - shim(vtable)"),
-        InstanceKind::ReifyShim(_, None) => write!(f, " - shim(reify)"),
-        InstanceKind::ReifyShim(_, Some(ReifyReason::FnPtr)) => write!(f, " - shim(reify-fnptr)"),
-        InstanceKind::ReifyShim(_, Some(ReifyReason::Vtable)) => write!(f, " - shim(reify-vtable)"),
-        InstanceKind::ThreadLocalShim(_) => write!(f, " - shim(tls)"),
-        InstanceKind::Intrinsic(_) => write!(f, " - intrinsic"),
-        InstanceKind::Virtual(_, num) => write!(f, " - virtual#{num}"),
-        InstanceKind::FnPtrShim(_, ty) => write!(f, " - shim({ty})"),
-        InstanceKind::ClosureOnceShim { .. } => write!(f, " - shim"),
-        InstanceKind::ConstructCoroutineInClosureShim { .. } => write!(f, " - shim"),
-        InstanceKind::DropGlue(_, None) => write!(f, " - shim(None)"),
-        InstanceKind::DropGlue(_, Some(ty)) => write!(f, " - shim(Some({ty}))"),
-        InstanceKind::CloneShim(_, ty) => write!(f, " - shim({ty})"),
-        InstanceKind::FnPtrAddrShim(_, ty) => write!(f, " - shim({ty})"),
-        InstanceKind::FutureDropPollShim(_, proxy_ty, impl_ty) => {
-            write!(f, " - dropshim({proxy_ty}-{impl_ty})")
-        }
-        InstanceKind::AsyncDropGlue(_, ty) => write!(f, " - shim({ty})"),
-        InstanceKind::AsyncDropGlueCtorShim(_, ty) => write!(f, " - shim(Some({ty}))"),
-    }
-}
-
-pub struct ShortInstance<'tcx>(pub Instance<'tcx>, pub usize);
-
-impl<'tcx> fmt::Display for ShortInstance<'tcx> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt_instance(f, self.0, Some(rustc_session::Limit(self.1)))
-    }
-}
-
 impl<'tcx> fmt::Display for Instance<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt_instance(f, *self, None)
+        ty::tls::with(|tcx| {
+            let mut cx = FmtPrinter::new(tcx, Namespace::ValueNS);
+            let instance = tcx.lift(*self).expect("could not lift for printing");
+            instance.print(&mut cx)?;
+            let s = cx.into_buffer();
+            f.write_str(&s)
+        })
     }
 }
 
@@ -610,23 +565,12 @@ impl<'tcx> Instance<'tcx> {
             Ok(None) => {
                 let type_length = type_length(args);
                 if !tcx.type_length_limit().value_within_limit(type_length) {
-                    let (shrunk, written_to_path) =
-                        shrunk_instance_name(tcx, Instance::new_raw(def_id, args));
-                    let mut path = PathBuf::new();
-                    let was_written = if let Some(path2) = written_to_path {
-                        path = path2;
-                        true
-                    } else {
-                        false
-                    };
                     tcx.dcx().emit_fatal(error::TypeLengthLimit {
                         // We don't use `def_span(def_id)` so that diagnostics point
                         // to the crate root during mono instead of to foreign items.
                         // This is arguably better.
                         span: span_or_local_def_span(),
-                        shrunk,
-                        was_written,
-                        path,
+                        instance: Instance::new_raw(def_id, args),
                         type_length,
                     });
                 } else {

diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
@@ -82,7 +82,7 @@ pub use self::context::{
     TyCtxtFeed, tls,
 };
 pub use self::fold::*;
-pub use self::instance::{Instance, InstanceKind, ReifyReason, ShortInstance, UnusedGenericParams};
+pub use self::instance::{Instance, InstanceKind, ReifyReason, UnusedGenericParams};
 pub use self::list::{List, ListWithCachedTypeInfo};
 pub use self::opaque_types::OpaqueTypeKey;
 pub use self::parameterized::ParameterizedOverTcx;

diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -1,5 +1,3 @@
-use std::path::PathBuf;
-
 use hir::def::Namespace;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sso::SsoHashSet;
@@ -8,7 +6,7 @@ use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use tracing::{debug, instrument, trace};
 
-use crate::ty::{self, GenericArg, ShortInstance, Ty, TyCtxt};
+use crate::ty::{self, GenericArg, Ty, TyCtxt};
 
 // `pretty` is a separate module only for organization.
 mod pretty;
@@ -323,6 +321,43 @@ impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for Ty<'tcx> {
     }
 }
 
+impl<'tcx, P: Printer<'tcx> + std::fmt::Write> Print<'tcx, P> for ty::Instance<'tcx> {
+    fn print(&self, cx: &mut P) -> Result<(), PrintError> {
+        cx.print_def_path(self.def_id(), self.args)?;
+        match self.def {
+            ty::InstanceKind::Item(_) => {}
+            ty::InstanceKind::VTableShim(_) => cx.write_str(" - shim(vtable)")?,
+            ty::InstanceKind::ReifyShim(_, None) => cx.write_str(" - shim(reify)")?,
+            ty::InstanceKind::ReifyShim(_, Some(ty::ReifyReason::FnPtr)) => {
+                cx.write_str(" - shim(reify-fnptr)")?
+            }
+            ty::InstanceKind::ReifyShim(_, Some(ty::ReifyReason::Vtable)) => {
+                cx.write_str(" - shim(reify-vtable)")?
+            }
+            ty::InstanceKind::ThreadLocalShim(_) => cx.write_str(" - shim(tls)")?,
+            ty::InstanceKind::Intrinsic(_) => cx.write_str(" - intrinsic")?,
+            ty::InstanceKind::Virtual(_, num) => cx.write_str(&format!(" - virtual#{num}"))?,
+            ty::InstanceKind::FnPtrShim(_, ty) => cx.write_str(&format!(" - shim({ty})"))?,
+            ty::InstanceKind::ClosureOnceShim { .. } => cx.write_str(" - shim")?,
+            ty::InstanceKind::ConstructCoroutineInClosureShim { .. } => cx.write_str(" - shim")?,
+            ty::InstanceKind::DropGlue(_, None) => cx.write_str(" - shim(None)")?,
+            ty::InstanceKind::DropGlue(_, Some(ty)) => {
+                cx.write_str(&format!(" - shim(Some({ty}))"))?
+            }
+            ty::InstanceKind::CloneShim(_, ty) => cx.write_str(&format!(" - shim({ty})"))?,
+            ty::InstanceKind::FnPtrAddrShim(_, ty) => cx.write_str(&format!(" - shim({ty})"))?,
+            ty::InstanceKind::FutureDropPollShim(_, proxy_ty, impl_ty) => {
+                cx.write_str(&format!(" - dropshim({proxy_ty}-{impl_ty})"))?
+            }
+            ty::InstanceKind::AsyncDropGlue(_, ty) => cx.write_str(&format!(" - shim({ty})"))?,
+            ty::InstanceKind::AsyncDropGlueCtorShim(_, ty) => {
+                cx.write_str(&format!(" - shim(Some({ty}))"))?
+            }
+        };
+        Ok(())
+    }
+}
+
 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> {
     fn print(&self, cx: &mut P) -> Result<(), PrintError> {
         cx.print_dyn_existential(self)
@@ -362,31 +397,3 @@ where
         with_no_trimmed_paths!(Self::print(t, fmt))
     }
 }
-
-/// Format instance name that is already known to be too long for rustc.
-/// Show only the first 2 types if it is longer than 32 characters to avoid blasting
-/// the user's terminal with thousands of lines of type-name.
-///
-/// If the type name is longer than before+after, it will be written to a file.
-pub fn shrunk_instance_name<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    instance: ty::Instance<'tcx>,
-) -> (String, Option<PathBuf>) {
-    let s = instance.to_string();
-
-    // Only use the shrunk version if it's really shorter.
-    // This also avoids the case where before and after slices overlap.
-    if s.chars().nth(33).is_some() {
-        let shrunk = format!("{}", ShortInstance(instance, 4));
-        if shrunk == s {
-            return (s, None);
-        }
-
-        let path = tcx.output_filenames(()).temp_path_for_diagnostic("long-type.txt");
-        let written_to_path = std::fs::write(&path, s).ok().map(|_| path);
-
-        (shrunk, written_to_path)
-    } else {
-        (s, None)
-    }
-}
diff --git a/compiler/rustc_monomorphize/messages.ftl b/compiler/rustc_monomorphize/messages.ftl
@@ -40,7 +40,10 @@ monomorphize_couldnt_dump_mono_stats =
     unexpected error occurred while dumping monomorphization stats: {$error}
 
 monomorphize_encountered_error_while_instantiating =
-    the above error was encountered while instantiating `{$formatted_item}`
+    the above error was encountered while instantiating `{$kind} {$instance}`
+
+monomorphize_encountered_error_while_instantiating_global_asm =
+    the above error was encountered while instantiating `global_asm`
 
 monomorphize_large_assignments =
     moving {$size} bytes
@@ -52,12 +55,10 @@ monomorphize_no_optimized_mir =
     .note = missing optimized MIR for this item (was the crate `{$crate_name}` compiled with `--emit=metadata`?)
 
 monomorphize_recursion_limit =
-    reached the recursion limit while instantiating `{$shrunk}`
+    reached the recursion limit while instantiating `{$instance}`
     .note = `{$def_path_str}` defined here
 
 monomorphize_start_not_found = using `fn main` requires the standard library
     .help = use `#![no_main]` to bypass the Rust generated entrypoint and declare a platform specific entrypoint yourself, usually with `#[no_mangle]`
 
 monomorphize_symbol_already_defined = symbol `{$symbol}` is already defined
-
-monomorphize_written_to_path = the full type name has been written to '{$path}'