move logic to a function

Author: HKalbasi

compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs

@@ -424,87 +424,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
 
                         match label {
                             Some((true, err_help_span, suggested_code)) => {
-                                /// User cannot make signature of a trait mutable
-                                /// without changing the trait. So we find if this
-                                /// error belongs to a trait and if so we move
-                                /// suggestion to the trait or disable it if it is
-                                /// out of scope of this crate
-                                let (is_trait_sig, local_trait) = {
-                                    if self.body.local_kind(local) != LocalKind::Arg {
-                                        (false, None)
-                                    } else {
-                                        let hir_map = self.infcx.tcx.hir();
-                                        let my_hir = hir_map.local_def_id_to_hir_id(
-                                            self.body.source.def_id().as_local().unwrap(),
-                                        );
-                                        match hir_map.find(hir_map.get_parent_node(my_hir)) {
-                                            Some(Node::Item(hir::Item {
-                                                kind:
-                                                    hir::ItemKind::Impl(hir::Impl {
-                                                        of_trait:
-                                                            Some(hir::TraitRef {
-                                                                path:
-                                                                    hir::Path {
-                                                                        res:
-                                                                            hir::def::Res::Def(_, td),
-                                                                        ..
-                                                                    },
-                                                                ..
-                                                            }),
-                                                        ..
-                                                    }),
-                                                ..
-                                            })) => {
-                                                (true, td.as_local().and_then(|tld| {
-                                                    let h = hir_map.local_def_id_to_hir_id(tld);
-                                                    match hir_map.find(h) {
-                                                        Some(Node::Item(hir::Item {
-                                                            kind: hir::ItemKind::Trait(
-                                                                _, _, _, _,
-                                                                items
-                                                            ),
-                                                            ..
-                                                        })) => {
-                                                            let mut f_in_trait_opt = None;
-                                                            for hir::TraitItemRef { id: fi, kind: k, .. } in *items {
-                                                                let hi = fi.hir_id();
-                                                                if !matches!(k, hir::AssocItemKind::Fn { .. }) {
-                                                                    continue;
-                                                                }
-                                                                if hir_map.name(hi) != hir_map.name(my_hir) {
-                                                                    continue;
-                                                                }
-                                                                f_in_trait_opt = Some(hi);
-                                                                break;
-                                                            }
-                                                            f_in_trait_opt.and_then(|f_in_trait| {
-                                                                match hir_map.find(f_in_trait) {
-                                                                    Some(Node::TraitItem(hir::TraitItem {
-                                                                        kind: hir::TraitItemKind::Fn(hir::FnSig {
-                                                                            decl: hir::FnDecl {
-                                                                                inputs,
-                                                                                ..
-                                                                            },
-                                                                            ..
-                                                                        }, _),
-                                                                        ..
-                                                                    })) => {
-                                                                        let hir::Ty { span, .. } = inputs[local.index() - 1];
-                                                                        Some(span)
-                                                                    },
-                                                                    _ => None,
-                                                                }
-                                                            })
-                                                            //Some(hir_map.span(h))
-                                                        }
-                                                        _ => None
-                                                    }
-                                                }))
-                                            }
-                                            _ => (false, None),
-                                        }
-                                    }
-                                };
+                                let (is_trait_sig, local_trait) = self.is_error_in_trait(local);
                                 if !is_trait_sig {
                                     err.span_suggestion(
                                         err_help_span,
@@ -595,6 +515,84 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
 
         err.buffer(&mut self.errors_buffer);
     }
+    
+    /// User cannot make signature of a trait mutable without changing the
+    /// trait. So we find if this error belongs to a trait and if so we move
+    /// suggestion to the trait or disable it if it is out of scope of this crate                            
+    fn is_error_in_trait(&self, local: Local) -> (bool, Option<Span>) {
+        if self.body.local_kind(local) != LocalKind::Arg {
+            return (false, None);
+        }
+        let hir_map = self.infcx.tcx.hir();
+        let my_hir = hir_map.local_def_id_to_hir_id(
+            self.body.source.def_id().as_local().unwrap(),
+        );
+        match hir_map.find(hir_map.get_parent_node(my_hir)) {
+            Some(Node::Item(hir::Item {
+                kind:
+                    hir::ItemKind::Impl(hir::Impl {
+                        of_trait:
+                            Some(hir::TraitRef {
+                                path:
+                                    hir::Path {
+                                        res:
+                                            hir::def::Res::Def(_, td),
+                                        ..
+                                    },
+                                ..
+                            }),
+                        ..
+                    }),
+                ..
+            })) => {
+                (true, td.as_local().and_then(|tld| {
+                    let h = hir_map.local_def_id_to_hir_id(tld);
+                    match hir_map.find(h) {
+                        Some(Node::Item(hir::Item {
+                            kind: hir::ItemKind::Trait(
+                                _, _, _, _,
+                                items
+                            ),
+                            ..
+                        })) => {
+                            let mut f_in_trait_opt = None;
+                            for hir::TraitItemRef { id: fi, kind: k, .. } in *items {
+                                let hi = fi.hir_id();
+                                if !matches!(k, hir::AssocItemKind::Fn { .. }) {
+                                    continue;
+                                }
+                                if hir_map.name(hi) != hir_map.name(my_hir) {
+                                    continue;
+                                }
+                                f_in_trait_opt = Some(hi);
+                                break;
+                            }
+                            f_in_trait_opt.and_then(|f_in_trait| {
+                                match hir_map.find(f_in_trait) {
+                                    Some(Node::TraitItem(hir::TraitItem {
+                                        kind: hir::TraitItemKind::Fn(hir::FnSig {
+                                            decl: hir::FnDecl {
+                                                inputs,
+                                                ..
+                                            },
+                                            ..
+                                        }, _),
+                                        ..
+                                    })) => {
+                                        let hir::Ty { span, .. } = inputs[local.index() - 1];
+                                        Some(span)
+                                    },
+                                    _ => None,
+                                }
+                            })
+                        }
+                        _ => None
+                    }
+                }))
+            }
+            _ => (false, None),
+        }
+    }
 
     // point to span of upvar making closure call require mutable borrow
     fn show_mutating_upvar(