remove old var_span_path_only

doc comment

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -224,10 +224,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
             }
 
-            use_spans.var_span_label_path_only(
-                &mut err,
-                format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
-            );
+            use_spans.var_path_only_subdiag(&mut err, desired_action);
 
             if !is_loop_move {
                 err.span_label(
@@ -404,10 +401,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let used = desired_action.as_general_verb_in_past_tense();
         let mut err =
             struct_span_err!(self, span, E0381, "{used} binding {desc}{isnt_initialized}");
-        use_spans.var_span_label_path_only(
-            &mut err,
-            format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
-        );
+        use_spans.var_path_only_subdiag(&mut err, desired_action);
 
         if let InitializationRequiringAction::PartialAssignment
         | InitializationRequiringAction::Assignment = desired_action
@@ -678,10 +672,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         err.span_label(borrow_span, format!("borrow of {} occurs here", borrow_msg));
         err.span_label(span, format!("move out of {} occurs here", value_msg));
 
-        borrow_spans.var_span_label_path_only(
-            &mut err,
-            format!("borrow occurs due to use{}", borrow_spans.describe()),
-        );
+        borrow_spans.var_path_only_subdiag(&mut err, crate::InitializationRequiringAction::Borrow);
 
         move_spans.var_span_label(
             &mut err,

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -595,11 +595,34 @@ impl UseSpans<'_> {
         }
     }
 
-    // Add a span label to the use of the captured variable, if it exists.
-    // only adds label to the `path_span`
-    pub(super) fn var_span_label_path_only(self, err: &mut Diagnostic, message: impl Into<String>) {
-        if let UseSpans::ClosureUse { path_span, .. } = self {
-            err.span_label(path_span, message);
+    /// Add a span label to the use of the captured variable, if it exists.
+    /// only adds label to the `path_span`
+    pub(super) fn var_path_only_subdiag(
+        self,
+        err: &mut Diagnostic,
+        action: crate::InitializationRequiringAction,
+    ) {
+        use crate::session_diagnostics::CaptureVarPathUseCause::*;
+        use crate::InitializationRequiringAction::*;
+        if let UseSpans::ClosureUse { generator_kind, path_span, .. } = self {
+            match generator_kind {
+                Some(_) => {
+                    err.subdiagnostic(match action {
+                        Borrow => BorrowInGenerator { path_span },
+                        MatchOn | Use => UseInGenerator { path_span },
+                        Assignment => AssignInGenerator { path_span },
+                        PartialAssignment => AssignPartInGenerator { path_span },
+                    });
+                }
+                None => {
+                    err.subdiagnostic(match action {
+                        Borrow => BorrowInClosure { path_span },
+                        MatchOn | Use => UseInClosure { path_span },
+                        Assignment => AssignInClosure { path_span },
+                        PartialAssignment => AssignPartInClosure { path_span },
+                    });
+                }
+            }
         }
     }
 

compiler/rustc_borrowck/src/session_diagnostics.rs

@@ -178,3 +178,47 @@ pub(crate) enum CaptureVarCause {
         var_span: Span,
     },
 }
+
+#[derive(Subdiagnostic)]
+pub(crate) enum CaptureVarPathUseCause {
+    #[label(borrowck_borrow_due_to_use_generator)]
+    BorrowInGenerator {
+        #[primary_span]
+        path_span: Span,
+    },
+    #[label(borrowck_use_due_to_use_generator)]
+    UseInGenerator {
+        #[primary_span]
+        path_span: Span,
+    },
+    #[label(borrowck_assign_due_to_use_generator)]
+    AssignInGenerator {
+        #[primary_span]
+        path_span: Span,
+    },
+    #[label(borrowck_assign_part_due_to_use_generator)]
+    AssignPartInGenerator {
+        #[primary_span]
+        path_span: Span,
+    },
+    #[label(borrowck_borrow_due_to_use_closure)]
+    BorrowInClosure {
+        #[primary_span]
+        path_span: Span,
+    },
+    #[label(borrowck_use_due_to_use_closure)]
+    UseInClosure {
+        #[primary_span]
+        path_span: Span,
+    },
+    #[label(borrowck_assign_due_to_use_closure)]
+    AssignInClosure {
+        #[primary_span]
+        path_span: Span,
+    },
+    #[label(borrowck_assign_part_due_to_use_closure)]
+    AssignPartInClosure {
+        #[primary_span]
+        path_span: Span,
+    },
+}

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

@@ -70,3 +70,27 @@ borrowck_var_borrow_by_use_place_in_closure =
 
 borrowck_var_borrow_by_use_place =
     borrow occurs due to use of {$place}
+
+borrowck_borrow_due_to_use_generator =
+    borrow occurs due to use in generator
+
+borrowck_use_due_to_use_generator =
+    use occurs due to use in generator
+
+borrowck_assign_due_to_use_generator =
+    assign occurs due to use in generator
+
+borrowck_assign_part_due_to_use_generator =
+    assign to part occurs due to use in generator
+
+borrowck_borrow_due_to_use_closure =
+    borrow occurs due to use in closure
+
+borrowck_use_due_to_use_closure =
+    use occurs due to use in closure
+
+borrowck_assign_due_to_use_closure =
+    assign occurs due to use in closure
+
+borrowck_assign_part_due_to_use_closure =
+    assign to part occurs due to use in closure