Migrate TupleTrailingCommaSuggestion

compiler/rustc_infer/messages.ftl

@@ -368,3 +368,5 @@ infer_sbfrit_box_return_expr = if you change the return type to expect trait obj
 
 infer_stp_wrap_one = try wrapping the pattern in `{$variant}`
 infer_stp_wrap_many = try wrapping the pattern in a variant of `{$path}`
+
+infer_tuple_trailing_comma = use a trailing comma to create a tuple with one element

compiler/rustc_infer/src/errors/mod.rs

@@ -1371,3 +1371,19 @@ impl AddToDiagnostic for SuggestTuplePatternMany {
         );
     }
 }
+
+#[derive(Subdiagnostic)]
+pub enum TupleTrailingCommaSuggestion {
+    #[suggestion(infer_tuple_trailing_comma, code = ",", applicability = "machine-applicable")]
+    OnlyComma {
+        #[primary_span]
+        span: Span,
+    },
+    #[multipart_suggestion(infer_tuple_trailing_comma, applicability = "machine-applicable")]
+    AlsoParentheses {
+        #[suggestion_part(code = "(")]
+        span_low: Span,
+        #[suggestion_part(code = ",)")]
+        span_high: Span,
+    },
+}

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -50,6 +50,7 @@ use super::region_constraints::GenericKind;
 use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePairs};
 
 use crate::errors;
+use crate::errors::TupleTrailingCommaSuggestion;
 use crate::infer;
 use crate::infer::error_reporting::nice_region_error::find_anon_type::find_anon_type;
 use crate::infer::ExpectedFound;
@@ -2110,22 +2111,18 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         let Ok(code) = self.tcx.sess().source_map().span_to_snippet(span)
             else { return };
 
-        let msg = "use a trailing comma to create a tuple with one element";
+        let sugg = if code.starts_with('(') && code.ends_with(')') {
-        if code.starts_with('(') && code.ends_with(')') {
             let before_close = span.hi() - BytePos::from_u32(1);
-            err.span_suggestion(
+            TupleTrailingCommaSuggestion::OnlyComma {
-                span.with_hi(before_close).shrink_to_hi(),
+                span: span.with_hi(before_close).shrink_to_hi(),
-                msg,
-                ",",
-                Applicability::MachineApplicable,
-            );
-        } else {
-            err.multipart_suggestion(
-                msg,
-                vec![(span.shrink_to_lo(), "(".into()), (span.shrink_to_hi(), ",)".into())],
-                Applicability::MachineApplicable,
-            );
             }
+        } else {
+            TupleTrailingCommaSuggestion::AlsoParentheses {
+                span_low: span.shrink_to_lo(),
+                span_high: span.shrink_to_hi(),
+            }
+        };
+        err.subdiagnostic(sugg);
     }
 
     fn values_str(