From c0fe46d6b72c96bda16bf62e7476e6d85ba68afe Mon Sep 17 00:00:00 2001
From: Oli Scherer <github333195615777966@oli-obk.de>
Date: Thu, 27 Mar 2025 12:08:00 +0000
Subject: [PATCH] Make missing optimized MIR error more informative

---
 compiler/rustc_monomorphize/messages.ftl     | 2 +-
 compiler/rustc_monomorphize/src/collector.rs | 1 +
 compiler/rustc_monomorphize/src/errors.rs    | 1 +
 tests/ui/rmeta/no_optitimized_mir.rs         | 2 +-
 tests/ui/rmeta/no_optitimized_mir.stderr     | 2 +-
 5 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_monomorphize/messages.ftl b/compiler/rustc_monomorphize/messages.ftl
index aae2d79c161..6b6653e7de0 100644
--- a/compiler/rustc_monomorphize/messages.ftl
+++ b/compiler/rustc_monomorphize/messages.ftl
@@ -48,7 +48,7 @@ monomorphize_large_assignments =
     .note = The current maximum size is {$limit}, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 
 monomorphize_no_optimized_mir =
-    missing optimized MIR for an item in the crate `{$crate_name}`
+    missing optimized MIR for `{$instance}` in the crate `{$crate_name}`
     .note = missing optimized MIR for this item (was the crate `{$crate_name}` compiled with `--emit=metadata`?)
 
 monomorphize_recursion_limit =
diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 2a1b20ba48b..6e676ac6b8d 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -989,6 +989,7 @@ fn should_codegen_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) ->
         tcx.dcx().emit_fatal(NoOptimizedMir {
             span: tcx.def_span(def_id),
             crate_name: tcx.crate_name(def_id.krate),
+            instance: instance.to_string(),
         });
     }
 
diff --git a/compiler/rustc_monomorphize/src/errors.rs b/compiler/rustc_monomorphize/src/errors.rs
index dffa372279f..adfe096f0cd 100644
--- a/compiler/rustc_monomorphize/src/errors.rs
+++ b/compiler/rustc_monomorphize/src/errors.rs
@@ -24,6 +24,7 @@ pub(crate) struct NoOptimizedMir {
     #[note]
     pub span: Span,
     pub crate_name: Symbol,
+    pub instance: String,
 }
 
 #[derive(LintDiagnostic)]
diff --git a/tests/ui/rmeta/no_optitimized_mir.rs b/tests/ui/rmeta/no_optitimized_mir.rs
index 708cdfc803f..c8ed00b039b 100644
--- a/tests/ui/rmeta/no_optitimized_mir.rs
+++ b/tests/ui/rmeta/no_optitimized_mir.rs
@@ -10,4 +10,4 @@ fn main() {
     rmeta_meta::missing_optimized_mir();
 }
 
-//~? ERROR missing optimized MIR for an item in the crate `rmeta_meta`
+//~? ERROR missing optimized MIR for `missing_optimized_mir` in the crate `rmeta_meta`
diff --git a/tests/ui/rmeta/no_optitimized_mir.stderr b/tests/ui/rmeta/no_optitimized_mir.stderr
index 92f22d78000..254f100aa7b 100644
--- a/tests/ui/rmeta/no_optitimized_mir.stderr
+++ b/tests/ui/rmeta/no_optitimized_mir.stderr
@@ -1,4 +1,4 @@
-error: missing optimized MIR for an item in the crate `rmeta_meta`
+error: missing optimized MIR for `missing_optimized_mir` in the crate `rmeta_meta`
    |
 note: missing optimized MIR for this item (was the crate `rmeta_meta` compiled with `--emit=metadata`?)
   --> $DIR/auxiliary/rmeta-meta.rs:10:1