Two mig-diag that fail ui test

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -16,6 +16,7 @@ use rustc_span::symbol::{kw, Symbol};
 use rustc_span::{sym, DesugaringKind, Span};
 
 use crate::region_infer::BlameConstraint;
+use crate::session_diagnostics::RequireBorrowLasts;
 use crate::{
     borrow_set::BorrowData, nll::ConstraintDescription, region_infer::Cause, MirBorrowckCtxt,
     WriteKind,
@@ -257,15 +258,14 @@ impl<'tcx> BorrowExplanation<'tcx> {
                         ),
                     );
                 } else {
-                    err.span_label(
+                    //FIXME: src/test/ui/consts/const-eval/const-eval-intrinsic-promotion.rs
+                    let sub_label = RequireBorrowLasts::Lasts {
+                        category: category.description(),
+                        borrow_desc,
+                        region_name,
                         span,
-                        format!(
-                            "{}requires that {}borrow lasts for `{}`",
-                            category.description(),
-                            borrow_desc,
-                            region_name,
-                        ),
-                    );
+                    };
+                    err.subdiagnostic(sub_label);
                 };
 
                 self.add_lifetime_bound_suggestion_to_diagnostic(err, &category, span, region_name);

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -10,6 +10,7 @@ use rustc_middle::ty::{self, DefIdTree, RegionVid, Ty};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 
+use crate::session_diagnostics::RegionNameLables;
 use crate::{nll::ToRegionVid, universal_regions::DefiningTy, MirBorrowckCtxt};
 
 /// A name for a particular region used in emitting diagnostics. This name could be a generated
@@ -106,7 +107,11 @@ impl RegionName {
         match &self.source {
             RegionNameSource::NamedFreeRegion(span)
             | RegionNameSource::NamedEarlyBoundRegion(span) => {
-                diag.span_label(*span, format!("lifetime `{self}` defined here"));
+                let name = format!("{self}");
+                diag.subdiagnostic(RegionNameLables::LifetimeDefinedHere {
+                    span: *span,
+                    rg_name: name,
+                });
             }
             RegionNameSource::SynthesizedFreeEnvRegion(span, note) => {
                 diag.span_label(*span, format!("lifetime `{self}` represents this closure's body"));

compiler/rustc_borrowck/src/session_diagnostics.rs

@@ -157,3 +157,25 @@ pub(crate) enum RequireStaticErr {
         multi_span: MultiSpan,
     },
 }
+
+#[derive(SessionSubdiagnostic)]
+pub(crate) enum RegionNameLables {
+    #[label(borrowck::lifetime_defined_here)]
+    LifetimeDefinedHere {
+        rg_name: String,
+        #[primary_span]
+        span: Span,
+    },
+}
+
+#[derive(SessionSubdiagnostic)]
+pub(crate) enum RequireBorrowLasts<'a> {
+    #[label(borrowck::outlive_constraint_need_borrow_lasts_for)]
+    Lasts {
+        category: &'a str,
+        borrow_desc: &'a str,
+        region_name: &'a RegionName,
+        #[primary_span]
+        span: Span,
+    },
+}

compiler/rustc_error_messages/locales/en-US/borrowck.ftl

@@ -58,3 +58,9 @@ borrowck_returned_lifetime_short =
 
 borrowck_used_impl_require_static =
     the used `impl` has a `'static` requirement
+
+borrowck_lifetime_defined_here =
+    lifetime `{$rg_name}` defined here
+
+borrowck_outlive_constraint_need_borrow_lasts_for =
+    {$category}requires that `{$borrow_desc}` lasts for `{$region_name}`