Make missing optimized MIR error more informative

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 =

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(),
         });
     }
 

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)]

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`

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