Move "elided lifetime in path" to subdiagnostic struct

This requires nested subdiagnostics.

2 files changed, 23 insertions, 18 deletions

diff --git a/compiler/rustc_errors/src/diagnostic_impls.rs b/compiler/rustc_errors/src/diagnostic_impls.rs
index 93b1c6775d6..2b10fcd8d6a 100644
--- a/compiler/rustc_errors/src/diagnostic_impls.rs
+++ b/compiler/rustc_errors/src/diagnostic_impls.rs
@@ -348,3 +348,11 @@ pub struct IndicateAnonymousLifetime {
     pub count: usize,
     pub suggestion: String,
 }
+
+#[derive(Subdiagnostic)]
+pub struct ElidedLifetimeInPathSubdiag {
+    #[subdiagnostic]
+    pub expected: ExpectedLifetimeParameter,
+    #[subdiagnostic]
+    pub indicate: Option<IndicateAnonymousLifetime>,
+}
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 8d6b22a9fa9..02b7ec18878 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -41,8 +41,8 @@ pub use diagnostic::{
     SubdiagMessageOp, Subdiagnostic,
 };
 pub use diagnostic_impls::{
-    DiagArgFromDisplay, DiagSymbolList, ExpectedLifetimeParameter, IndicateAnonymousLifetime,
-    SingleLabelManySpans,
+    DiagArgFromDisplay, DiagSymbolList, ElidedLifetimeInPathSubdiag, ExpectedLifetimeParameter,
+    IndicateAnonymousLifetime, SingleLabelManySpans,
 };
 pub use emitter::ColorConfig;
 pub use rustc_error_messages::{
@@ -1912,27 +1912,24 @@ impl Level {
 }
 
 // FIXME(eddyb) this doesn't belong here AFAICT, should be moved to callsite.
-pub fn add_elided_lifetime_in_path_suggestion<G: EmissionGuarantee>(
+pub fn elided_lifetime_in_path_suggestion(
     source_map: &SourceMap,
-    diag: &mut Diag<'_, G>,
     n: usize,
     path_span: Span,
     incl_angl_brckt: bool,
     insertion_span: Span,
-) {
-    diag.subdiagnostic(diag.dcx, ExpectedLifetimeParameter { span: path_span, count: n });
-    if !source_map.is_span_accessible(insertion_span) {
-        // Do not try to suggest anything if generated by a proc-macro.
-        return;
-    }
-    let anon_lts = vec!["'_"; n].join(", ");
-    let suggestion =
-        if incl_angl_brckt { format!("<{anon_lts}>") } else { format!("{anon_lts}, ") };
-
-    diag.subdiagnostic(
-        diag.dcx,
-        IndicateAnonymousLifetime { span: insertion_span.shrink_to_hi(), count: n, suggestion },
-    );
+) -> ElidedLifetimeInPathSubdiag {
+    let expected = ExpectedLifetimeParameter { span: path_span, count: n };
+    // Do not try to suggest anything if generated by a proc-macro.
+    let indicate = source_map.is_span_accessible(insertion_span).then(|| {
+        let anon_lts = vec!["'_"; n].join(", ");
+        let suggestion =
+            if incl_angl_brckt { format!("<{anon_lts}>") } else { format!("{anon_lts}, ") };
+
+        IndicateAnonymousLifetime { span: insertion_span.shrink_to_hi(), count: n, suggestion }
+    });
+
+    ElidedLifetimeInPathSubdiag { expected, indicate }
 }
 
 pub fn report_ambiguity_error<'a, G: EmissionGuarantee>(