Suggest removing unused tuple fields if they are the last fields

compiler/rustc_passes/src/dead.rs

@@ -23,8 +23,7 @@ use rustc_target::abi::FieldIdx;
 use std::mem;
 
 use crate::errors::{
-    ChangeFieldsToBeOfUnitType, IgnoredDerivedImpls, MultipleDeadCodes, ParentInfo,
-    UselessAssignment,
+    ChangeFields, IgnoredDerivedImpls, MultipleDeadCodes, ParentInfo, UselessAssignment,
 };
 
 // Any local node that may call something in its body block should be
@@ -993,17 +992,50 @@ impl<'tcx> DeadVisitor<'tcx> {
             };
 
         let diag = match report_on {
-            ReportOn::TupleField => MultipleDeadCodes::UnusedTupleStructFields {
-                multiple,
-                num,
-                descr,
-                participle,
-                name_list,
-                change_fields_suggestion: ChangeFieldsToBeOfUnitType { num, spans: spans.clone() },
-                parent_info,
-                ignored_derived_impls,
-            },
+            ReportOn::TupleField => {
+                let tuple_fields = if let Some(parent_id) = parent_item
+                    && let node = tcx.hir_node_by_def_id(parent_id)
+                    && let hir::Node::Item(hir::Item {
+                        kind: hir::ItemKind::Struct(hir::VariantData::Tuple(fields, _, _), _),
+                        ..
+                    }) = node
+                {
+                    *fields
+                } else {
+                    &[]
+                };
 
+                let trailing_tuple_fields = if tuple_fields.len() >= dead_codes.len() {
+                    LocalDefIdSet::from_iter(
+                        tuple_fields
+                            .iter()
+                            .skip(tuple_fields.len() - dead_codes.len())
+                            .map(|f| f.def_id),
+                    )
+                } else {
+                    LocalDefIdSet::default()
+                };
+
+                let fields_suggestion =
+                    // Suggest removal if all tuple fields are at the end.
+                    // Otherwise suggest removal or changing to unit type
+                    if dead_codes.iter().all(|dc| trailing_tuple_fields.contains(&dc.def_id)) {
+                        ChangeFields::Remove { num }
+                    } else {
+                        ChangeFields::ChangeToUnitTypeOrRemove { num, spans: spans.clone() }
+                    };
+
+                MultipleDeadCodes::UnusedTupleStructFields {
+                    multiple,
+                    num,
+                    descr,
+                    participle,
+                    name_list,
+                    change_fields_suggestion: fields_suggestion,
+                    parent_info,
+                    ignored_derived_impls,
+                }
+            }
             ReportOn::NamedField => MultipleDeadCodes::DeadCodes {
                 multiple,
                 num,

compiler/rustc_passes/src/errors.rs

@@ -1589,7 +1589,7 @@ pub enum MultipleDeadCodes<'tcx> {
         participle: &'tcx str,
         name_list: DiagSymbolList,
         #[subdiagnostic]
-        change_fields_suggestion: ChangeFieldsToBeOfUnitType,
+        change_fields_suggestion: ChangeFields,
         #[subdiagnostic]
         parent_info: Option<ParentInfo<'tcx>>,
         #[subdiagnostic]
@@ -1616,11 +1616,18 @@ pub struct IgnoredDerivedImpls {
 }
 
 #[derive(Subdiagnostic)]
-#[multipart_suggestion(passes_change_fields_to_be_of_unit_type, applicability = "has-placeholders")]
-pub struct ChangeFieldsToBeOfUnitType {
-    pub num: usize,
-    #[suggestion_part(code = "()")]
-    pub spans: Vec<Span>,
+pub enum ChangeFields {
+    #[multipart_suggestion(
+        passes_change_fields_to_be_of_unit_type,
+        applicability = "has-placeholders"
+    )]
+    ChangeToUnitTypeOrRemove {
+        num: usize,
+        #[suggestion_part(code = "()")]
+        spans: Vec<Span>,
+    },
+    #[help(passes_remove_fields)]
+    Remove { num: usize },
 }
 
 #[derive(Diagnostic)]