rustc: Panic by default in DefIdTree::parent

Only crate root def-ids don't have a parent, and in majority of cases the argument of `DefIdTree::parent` cannot be a crate root.
So we now panic by default in `parent` and introduce a new non-panicing function `opt_parent` for cases where the argument can be a crate root.

Same applies to `local_parent`/`opt_local_parent`.

Author: petrochenkov

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -90,7 +90,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         {
             if let ty::FnDef(id, _) = *literal.ty().kind() {
                 debug!("add_moved_or_invoked_closure_note: id={:?}", id);
-                if self.infcx.tcx.parent(id) == self.infcx.tcx.lang_items().fn_once_trait() {
+                if Some(self.infcx.tcx.parent(id)) == self.infcx.tcx.lang_items().fn_once_trait() {
                     let closure = match args.first() {
                         Some(Operand::Copy(ref place)) | Some(Operand::Move(ref place))
                             if target == place.local_or_deref_local() =>

compiler/rustc_codegen_llvm/src/debuginfo/utils.rs

@@ -46,7 +46,7 @@ pub fn DIB<'a, 'll>(cx: &'a CodegenCx<'ll, '_>) -> &'a DIBuilder<'ll> {
 }
 
 pub fn get_namespace_for_item<'ll>(cx: &CodegenCx<'ll, '_>, def_id: DefId) -> &'ll DIScope {
-    item_namespace(cx, cx.tcx.parent(def_id).expect("get_namespace_for_item: missing parent?"))
+    item_namespace(cx, cx.tcx.parent(def_id))
 }
 
 #[derive(Debug, PartialEq, Eq)]

compiler/rustc_const_eval/src/const_eval/fn_queries.rs

@@ -17,7 +17,7 @@ pub fn is_unstable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
 }
 
 pub fn is_parent_const_impl_raw(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
-    let parent_id = tcx.local_parent(def_id).unwrap();
+    let parent_id = tcx.local_parent(def_id);
     tcx.def_kind(parent_id) == DefKind::Impl
         && tcx.impl_constness(parent_id) == hir::Constness::Const
 }

compiler/rustc_const_eval/src/util/call_kind.rs

@@ -128,9 +128,9 @@ pub fn call_kind<'tcx>(
         } else {
             None
         };
-        let parent_self_ty = tcx
-            .parent(method_did)
-            .filter(|did| tcx.def_kind(*did) == rustc_hir::def::DefKind::Impl)
+        let parent_did = tcx.parent(method_did);
+        let parent_self_ty = (tcx.def_kind(parent_did) == rustc_hir::def::DefKind::Impl)
+            .then_some(parent_did)
             .and_then(|did| match tcx.type_of(did).kind() {
                 ty::Adt(def, ..) => Some(def.did()),
                 _ => None,

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

@@ -341,7 +341,7 @@ impl InferenceDiagnosticsData {
 
 impl InferenceDiagnosticsParentData {
     fn for_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<InferenceDiagnosticsParentData> {
-        let parent_def_id = tcx.parent(def_id)?;
+        let parent_def_id = tcx.parent(def_id);
 
         let parent_name =
             tcx.def_key(parent_def_id).disambiguated_data.data.get_opt_name()?.to_string();
@@ -854,10 +854,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         if let Some((DefKind::AssocFn, def_id)) =
             self.in_progress_typeck_results?.borrow().type_dependent_def(hir_id)
         {
-            return self
-                .tcx
-                .parent(def_id)
-                .filter(|&parent_def_id| self.tcx.is_trait(parent_def_id));
+            let parent_def_id = self.tcx.parent(def_id);
+            return self.tcx.is_trait(parent_def_id).then_some(parent_def_id);
         }
 
         None

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/util.rs

@@ -42,7 +42,7 @@ pub fn find_param_with_region<'tcx>(
     let (id, bound_region) = match *anon_region {
         ty::ReFree(ref free_region) => (free_region.scope, free_region.bound_region),
         ty::ReEarlyBound(ebr) => {
-            (tcx.parent(ebr.def_id).unwrap(), ty::BoundRegionKind::BrNamed(ebr.def_id, ebr.name))
+            (tcx.parent(ebr.def_id), ty::BoundRegionKind::BrNamed(ebr.def_id, ebr.name))
         }
         _ => return None, // not a free region
     };

compiler/rustc_lint/src/types.rs

@@ -1471,7 +1471,7 @@ impl InvalidAtomicOrdering {
             && let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def()
             // skip extension traits, only lint functions from the standard library
             && cx.tcx.trait_id_of_impl(impl_did).is_none()
-            && let Some(parent) = cx.tcx.parent(adt.did())
+            && let parent = cx.tcx.parent(adt.did())
             && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
             && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
         {
@@ -1486,9 +1486,9 @@ impl InvalidAtomicOrdering {
         orderings.iter().any(|ordering| {
             tcx.item_name(did) == *ordering && {
                 let parent = tcx.parent(did);
-                parent == atomic_ordering
+                Some(parent) == atomic_ordering
                     // needed in case this is a ctor, not a variant
-                    || parent.map_or(false, |parent| tcx.parent(parent) == atomic_ordering)
+                    || tcx.opt_parent(parent) == atomic_ordering
             }
         })
     }

compiler/rustc_middle/src/hir/map/mod.rs

@@ -546,7 +546,7 @@ impl<'hir> Map<'hir> {
         let def_kind = self.tcx.def_kind(def_id);
         match def_kind {
             DefKind::Trait | DefKind::TraitAlias => def_id,
-            DefKind::TyParam | DefKind::ConstParam => self.tcx.local_parent(def_id).unwrap(),
+            DefKind::TyParam | DefKind::ConstParam => self.tcx.local_parent(def_id),
             _ => bug!("ty_param_owner: {:?} is a {:?} not a type parameter", def_id, def_kind),
         }
     }

compiler/rustc_middle/src/middle/stability.rs

@@ -289,7 +289,7 @@ fn suggestion_for_allocator_api(
     feature: Symbol,
 ) -> Option<(Span, String, String, Applicability)> {
     if feature == sym::allocator_api {
-        if let Some(trait_) = tcx.parent(def_id) {
+        if let Some(trait_) = tcx.opt_parent(def_id) {
             if tcx.is_diagnostic_item(sym::Vec, trait_) {
                 let sm = tcx.sess.parse_sess.source_map();
                 let inner_types = sm.span_extend_to_prev_char(span, '<', true);

compiler/rustc_middle/src/ty/context.rs

@@ -1491,7 +1491,7 @@ impl<'tcx> TyCtxt<'tcx> {
                 (free_region.scope.expect_local(), free_region.bound_region)
             }
             ty::ReEarlyBound(ref ebr) => (
-                self.parent(ebr.def_id).unwrap().expect_local(),
+                self.local_parent(ebr.def_id.expect_local()),
                 ty::BoundRegionKind::BrNamed(ebr.def_id, ebr.name),
             ),
             _ => return None, // not a free region

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -108,7 +108,7 @@ impl<'tcx> Ty<'tcx> {
             | Placeholder(_)
             | Error(_) => false,
             Opaque(did, substs) => {
-                let parent = tcx.parent(*did).expect("opaque types always have a parent");
+                let parent = tcx.parent(*did);
                 if let hir::def::DefKind::TyAlias | hir::def::DefKind::AssocTy = tcx.def_kind(parent)
                     && let Opaque(parent_did, _) = tcx.type_of(parent).kind()
                     && parent_did == did

compiler/rustc_middle/src/ty/mod.rs

@@ -290,11 +290,28 @@ pub struct ClosureSizeProfileData<'tcx> {
 }
 
 pub trait DefIdTree: Copy {
-    fn parent(self, id: DefId) -> Option<DefId>;
+    fn opt_parent(self, id: DefId) -> Option<DefId>;
 
     #[inline]
-    fn local_parent(self, id: LocalDefId) -> Option<LocalDefId> {
-        Some(self.parent(id.to_def_id())?.expect_local())
+    #[track_caller]
+    fn parent(self, id: DefId) -> DefId {
+        match self.opt_parent(id) {
+            Some(id) => id,
+            // not `unwrap_or_else` to avoid breaking caller tracking
+            None => bug!("{id:?} doesn't have a parent"),
+        }
+    }
+
+    #[inline]
+    #[track_caller]
+    fn opt_local_parent(self, id: LocalDefId) -> Option<LocalDefId> {
+        self.opt_parent(id.to_def_id()).map(DefId::expect_local)
+    }
+
+    #[inline]
+    #[track_caller]
+    fn local_parent(self, id: LocalDefId) -> LocalDefId {
+        self.parent(id.to_def_id()).expect_local()
     }
 
     fn is_descendant_of(self, mut descendant: DefId, ancestor: DefId) -> bool {
@@ -303,7 +320,7 @@ pub trait DefIdTree: Copy {
         }
 
         while descendant != ancestor {
-            match self.parent(descendant) {
+            match self.opt_parent(descendant) {
                 Some(parent) => descendant = parent,
                 None => return false,
             }
@@ -313,7 +330,8 @@ pub trait DefIdTree: Copy {
 }
 
 impl<'tcx> DefIdTree for TyCtxt<'tcx> {
-    fn parent(self, id: DefId) -> Option<DefId> {
+    #[inline]
+    fn opt_parent(self, id: DefId) -> Option<DefId> {
         self.def_key(id).parent.map(|index| DefId { index, ..id })
     }
 }
@@ -2123,17 +2141,17 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn expect_variant_res(self, res: Res) -> &'tcx VariantDef {
         match res {
             Res::Def(DefKind::Variant, did) => {
-                let enum_did = self.parent(did).unwrap();
+                let enum_did = self.parent(did);
                 self.adt_def(enum_did).variant_with_id(did)
             }
             Res::Def(DefKind::Struct | DefKind::Union, did) => self.adt_def(did).non_enum_variant(),
             Res::Def(DefKind::Ctor(CtorOf::Variant, ..), variant_ctor_did) => {
-                let variant_did = self.parent(variant_ctor_did).unwrap();
-                let enum_did = self.parent(variant_did).unwrap();
+                let variant_did = self.parent(variant_ctor_did);
+                let enum_did = self.parent(variant_did);
                 self.adt_def(enum_did).variant_with_ctor_id(variant_ctor_did)
             }
             Res::Def(DefKind::Ctor(CtorOf::Struct, ..), ctor_did) => {
-                let struct_did = self.parent(ctor_did).expect("struct ctor has no parent");
+                let struct_did = self.parent(ctor_did);
                 self.adt_def(struct_did).non_enum_variant()
             }
             _ => bug!("expect_variant_res used with unexpected res {:?}", res),

compiler/rustc_middle/src/ty/print/mod.rs

@@ -235,11 +235,11 @@ pub trait Printer<'tcx>: Sized {
         // as the trait.
         let in_self_mod = match characteristic_def_id_of_type(self_ty) {
             None => false,
-            Some(ty_def_id) => self.tcx().parent(ty_def_id) == Some(parent_def_id),
+            Some(ty_def_id) => self.tcx().parent(ty_def_id) == parent_def_id,
         };
         let in_trait_mod = match impl_trait_ref {
             None => false,
-            Some(trait_ref) => self.tcx().parent(trait_ref.def_id) == Some(parent_def_id),
+            Some(trait_ref) => self.tcx().parent(trait_ref.def_id) == parent_def_id,
         };
 
         if !in_self_mod && !in_trait_mod {

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -408,7 +408,7 @@ pub trait PrettyPrinter<'tcx>:
             return Ok((self, false));
         };
 
-        let actual_parent = self.tcx().parent(def_id);
+        let actual_parent = self.tcx().opt_parent(def_id);
         debug!(
             "try_print_visible_def_path: visible_parent={:?} actual_parent={:?}",
             visible_parent, actual_parent,
@@ -643,7 +643,7 @@ pub trait PrettyPrinter<'tcx>:
                     return Ok(self);
                 }
 
-                let parent = self.tcx().parent(def_id).expect("opaque types always have a parent");
+                let parent = self.tcx().parent(def_id);
                 match self.tcx().def_kind(parent) {
                     DefKind::TyAlias | DefKind::AssocTy => {
                         if let ty::Opaque(d, _) = *self.tcx().type_of(parent).kind() {

compiler/rustc_middle/src/ty/sty.rs

@@ -1798,7 +1798,7 @@ impl<'tcx> Region<'tcx> {
     /// function might return the `DefId` of a closure.
     pub fn free_region_binding_scope(self, tcx: TyCtxt<'_>) -> DefId {
         match *self {
-            ty::ReEarlyBound(br) => tcx.parent(br.def_id).unwrap(),
+            ty::ReEarlyBound(br) => tcx.parent(br.def_id),
             ty::ReFree(fr) => fr.scope,
             _ => bug!("free_region_binding_scope invoked on inappropriate region: {:?}", self),
         }

compiler/rustc_middle/src/ty/util.rs

@@ -142,10 +142,10 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn res_generics_def_id(self, res: Res) -> Option<DefId> {
         match res {
             Res::Def(DefKind::Ctor(CtorOf::Variant, _), def_id) => {
-                Some(self.parent(def_id).and_then(|def_id| self.parent(def_id)).unwrap())
+                Some(self.parent(self.parent(def_id)))
             }
             Res::Def(DefKind::Variant | DefKind::Ctor(CtorOf::Struct, _), def_id) => {
-                Some(self.parent(def_id).unwrap())
+                Some(self.parent(def_id))
             }
             // Other `DefKind`s don't have generics and would ICE when calling
             // `generics_of`.
@@ -500,9 +500,7 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn typeck_root_def_id(self, def_id: DefId) -> DefId {
         let mut def_id = def_id;
         while self.is_typeck_child(def_id) {
-            def_id = self.parent(def_id).unwrap_or_else(|| {
-                bug!("closure {:?} has no parent", def_id);
-            });
+            def_id = self.parent(def_id);
         }
         def_id
     }

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -377,15 +377,15 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
     ) -> PatKind<'tcx> {
         let res = match res {
             Res::Def(DefKind::Ctor(CtorOf::Variant, ..), variant_ctor_id) => {
-                let variant_id = self.tcx.parent(variant_ctor_id).unwrap();
+                let variant_id = self.tcx.parent(variant_ctor_id);
                 Res::Def(DefKind::Variant, variant_id)
             }
             res => res,
         };
 
         let mut kind = match res {
             Res::Def(DefKind::Variant, variant_id) => {
-                let enum_id = self.tcx.parent(variant_id).unwrap();
+                let enum_id = self.tcx.parent(variant_id);
                 let adt_def = self.tcx.adt_def(enum_id);
                 if adt_def.is_enum() {
                     let substs = match ty.kind() {

compiler/rustc_monomorphize/src/partitioning/default.rs

@@ -352,7 +352,7 @@ fn compute_codegen_unit_name(
             cgu_def_id = None;
         }
 
-        current_def_id = tcx.parent(current_def_id).unwrap();
+        current_def_id = tcx.parent(current_def_id);
     }
 
     let cgu_def_id = cgu_def_id.unwrap();

compiler/rustc_passes/src/dead.rs

@@ -88,15 +88,15 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
             _ if self.in_pat => {}
             Res::PrimTy(..) | Res::SelfCtor(..) | Res::Local(..) => {}
             Res::Def(DefKind::Ctor(CtorOf::Variant, ..), ctor_def_id) => {
-                let variant_id = self.tcx.parent(ctor_def_id).unwrap();
-                let enum_id = self.tcx.parent(variant_id).unwrap();
+                let variant_id = self.tcx.parent(ctor_def_id);
+                let enum_id = self.tcx.parent(variant_id);
                 self.check_def_id(enum_id);
                 if !self.ignore_variant_stack.contains(&ctor_def_id) {
                     self.check_def_id(variant_id);
                 }
             }
             Res::Def(DefKind::Variant, variant_id) => {
-                let enum_id = self.tcx.parent(variant_id).unwrap();
+                let enum_id = self.tcx.parent(variant_id);
                 self.check_def_id(enum_id);
                 if !self.ignore_variant_stack.contains(&variant_id) {
                     self.check_def_id(variant_id);

compiler/rustc_passes/src/entry.rs

@@ -27,7 +27,7 @@ struct EntryContext<'tcx> {
 
 impl<'tcx> ItemLikeVisitor<'tcx> for EntryContext<'tcx> {
     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
-        let at_root = self.tcx.local_parent(item.def_id) == Some(CRATE_DEF_ID);
+        let at_root = self.tcx.opt_local_parent(item.def_id) == Some(CRATE_DEF_ID);
         find_item(item, self, at_root);
     }
 

compiler/rustc_passes/src/liveness.rs

@@ -332,9 +332,9 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
         let def_id = local_def_id.to_def_id();
 
         // Don't run unused pass for #[derive()]
-        if let Some(parent) = self.tcx.parent(def_id)
-            && let DefKind::Impl = self.tcx.def_kind(parent.expect_local())
-            && self.tcx.has_attr(parent, sym::automatically_derived)
+        let parent = self.tcx.local_parent(local_def_id);
+        if let DefKind::Impl = self.tcx.def_kind(parent)
+            && self.tcx.has_attr(parent.to_def_id(), sym::automatically_derived)
         {
             return;
         }

compiler/rustc_passes/src/reachable.rs

@@ -280,8 +280,7 @@ impl<'tcx> ReachableContext<'tcx> {
                     self.visit_nested_body(body);
                 }
                 hir::ImplItemKind::Fn(_, body) => {
-                    let impl_def_id =
-                        self.tcx.parent(search_item.to_def_id()).unwrap().expect_local();
+                    let impl_def_id = self.tcx.local_parent(search_item);
                     if method_might_be_inlined(self.tcx, impl_item, impl_def_id) {
                         self.visit_nested_body(body)
                     }

compiler/rustc_privacy/src/lib.rs

@@ -24,7 +24,8 @@ use rustc_middle::thir::abstract_const::Node as ACNode;
 use rustc_middle::ty::fold::TypeVisitor;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::subst::InternalSubsts;
-use rustc_middle::ty::{self, Const, GenericParamDefKind, TraitRef, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, Const, DefIdTree, GenericParamDefKind};
+use rustc_middle::ty::{TraitRef, Ty, TyCtxt, TypeFoldable};
 use rustc_session::lint;
 use rustc_span::hygiene::Transparency;
 use rustc_span::symbol::{kw, Ident};
@@ -456,9 +457,7 @@ impl<'tcx> EmbargoVisitor<'tcx> {
             return;
         }
 
-        let item_def_id = local_def_id.to_def_id();
-        let macro_module_def_id =
-            ty::DefIdTree::parent(self.tcx, item_def_id).unwrap().expect_local();
+        let macro_module_def_id = self.tcx.local_parent(local_def_id);
         if self.tcx.hir().opt_def_kind(macro_module_def_id) != Some(DefKind::Mod) {
             // The macro's parent doesn't correspond to a `mod`, return early (#63164, #65252).
             return;
@@ -477,8 +476,7 @@ impl<'tcx> EmbargoVisitor<'tcx> {
             if changed_reachability || module_def_id == CRATE_DEF_ID {
                 break;
             }
-            module_def_id =
-                ty::DefIdTree::parent(self.tcx, module_def_id.to_def_id()).unwrap().expect_local();
+            module_def_id = self.tcx.local_parent(module_def_id);
         }
     }
 

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -1388,7 +1388,7 @@ impl<'a, 'b> Visitor<'b> for BuildReducedGraphVisitor<'a, 'b> {
             && self
                 .r
                 .trait_impl_items
-                .contains(&ty::DefIdTree::parent(&*self.r, def_id).unwrap().expect_local()))
+                .contains(&ty::DefIdTree::local_parent(&*self.r, local_def_id)))
         {
             // Trait impl item visibility is inherited from its trait when not specified
             // explicitly. In that case we cannot determine it here in early resolve,