Simplify astconv item def id handling

compiler/rustc_hir_analysis/src/astconv/errors.rs

@@ -177,11 +177,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .all_traits()
             .filter(|trait_def_id| {
                 let viz = self.tcx().visibility(*trait_def_id);
-                if let Some(def_id) = self.item_def_id() {
-                    viz.is_accessible_from(def_id, self.tcx())
-                } else {
-                    viz.is_visible_locally()
-                }
+                let def_id = self.item_def_id();
+                viz.is_accessible_from(def_id, self.tcx())
             })
             .collect();
 

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -54,7 +54,7 @@ pub struct PathSeg(pub DefId, pub usize);
 pub trait AstConv<'tcx> {
     fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
 
-    fn item_def_id(&self) -> Option<DefId>;
+    fn item_def_id(&self) -> DefId;
 
     /// Returns predicates in scope of the form `X: Foo<T>`, where `X`
     /// is a type parameter `X` with the given id `def_id` and T
@@ -2079,17 +2079,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
             debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
 
-            let parent_def_id = def_id
-                .and_then(|def_id| {
-                    def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
-                })
+            let parent_def_id = def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
                 .map(|hir_id| tcx.hir().get_parent_item(hir_id).to_def_id());
 
             debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
 
             // If the trait in segment is the same as the trait defining the item,
             // use the `<Self as ..>` syntax in the error.
-            let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
+            let is_part_of_self_trait_constraints = def_id == trait_def_id;
             let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
 
             let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {

compiler/rustc_hir_analysis/src/collect.rs

@@ -379,8 +379,8 @@ impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
         self.tcx
     }
 
-    fn item_def_id(&self) -> Option<DefId> {
-        Some(self.item_def_id)
+    fn item_def_id(&self) -> DefId {
+        self.item_def_id
     }
 
     fn get_type_parameter_bounds(

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -194,8 +194,8 @@ impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
         self.tcx
     }
 
-    fn item_def_id(&self) -> Option<DefId> {
-        None
+    fn item_def_id(&self) -> DefId {
+        self.body_id.owner.to_def_id()
     }
 
     fn get_type_parameter_bounds(