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`.

13 files changed, 27 insertions, 33 deletions

diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index d458deddae3..eea4eef9065 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -421,7 +421,7 @@ impl Clean<GenericParamDef> for ty::GenericParamDef {
                     // `self_def_id` set, we override it here.
                     // See https://github.com/rust-lang/rust/issues/85454
                     if let QPath { ref mut self_def_id, .. } = default {
-                        *self_def_id = cx.tcx.parent(self.def_id);
+                        *self_def_id = Some(cx.tcx.parent(self.def_id));
                     }
 
                     Some(default)
@@ -1068,7 +1068,7 @@ impl Clean<Item> for hir::ImplItem<'_> {
             let mut what_rustc_thinks =
                 Item::from_def_id_and_parts(local_did, Some(self.ident.name), inner, cx);
 
-            let impl_ref = cx.tcx.parent(local_did).and_then(|did| cx.tcx.impl_trait_ref(did));
+            let impl_ref = cx.tcx.impl_trait_ref(cx.tcx.local_parent(self.def_id));
 
             // Trait impl items always inherit the impl's visibility --
             // we don't want to show `pub`.
@@ -1260,7 +1260,7 @@ impl Clean<Item> for ty::AssocItem {
         let mut what_rustc_thinks =
             Item::from_def_id_and_parts(self.def_id, Some(self.name), kind, cx);
 
-        let impl_ref = tcx.parent(self.def_id).and_then(|did| tcx.impl_trait_ref(did));
+        let impl_ref = tcx.impl_trait_ref(tcx.parent(self.def_id));
 
         // Trait impl items always inherit the impl's visibility --
         // we don't want to show `pub`.
@@ -1742,9 +1742,7 @@ fn clean_field(def_id: DefId, name: Symbol, ty: Type, cx: &mut DocContext<'_>) -
 }
 
 fn is_field_vis_inherited(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-    let parent = tcx
-        .parent(def_id)
-        .expect("is_field_vis_inherited can only be called on struct or variant fields");
+    let parent = tcx.parent(def_id);
     match tcx.def_kind(parent) {
         DefKind::Struct | DefKind::Union => false,
         DefKind::Variant => true,
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index abfc5b80a3e..3a2f24d719c 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -455,7 +455,7 @@ crate fn find_nearest_parent_module(tcx: TyCtxt<'_>, def_id: DefId) -> Option<De
         let mut current = def_id;
         // The immediate parent might not always be a module.
         // Find the first parent which is.
-        while let Some(parent) = tcx.parent(current) {
+        while let Some(parent) = tcx.opt_parent(current) {
             if tcx.def_kind(parent) == DefKind::Mod {
                 return Some(parent);
             }
diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 118807a8286..528eb6410cb 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -563,7 +563,7 @@ crate fn href_with_root_path(
     let did = match def_kind {
         DefKind::AssocTy | DefKind::AssocFn | DefKind::AssocConst | DefKind::Variant => {
             // documented on their parent's page
-            tcx.parent(did).unwrap()
+            tcx.parent(did)
         }
         _ => did,
     };
diff --git a/src/librustdoc/passes/calculate_doc_coverage.rs b/src/librustdoc/passes/calculate_doc_coverage.rs
index 33d83aa339d..0d40ef4c600 100644
--- a/src/librustdoc/passes/calculate_doc_coverage.rs
+++ b/src/librustdoc/passes/calculate_doc_coverage.rs
@@ -239,7 +239,7 @@ impl<'a, 'b> DocVisitor for CoverageCalculator<'a, 'b> {
                 let should_be_ignored = i
                     .item_id
                     .as_def_id()
-                    .and_then(|def_id| self.ctx.tcx.parent(def_id))
+                    .and_then(|def_id| self.ctx.tcx.opt_parent(def_id))
                     .and_then(|def_id| self.ctx.tcx.hir().get_if_local(def_id))
                     .map(|node| {
                         matches!(
diff --git a/src/librustdoc/passes/collect_intra_doc_links.rs b/src/librustdoc/passes/collect_intra_doc_links.rs
index 42e87f3f961..7a68a6e523b 100644
--- a/src/librustdoc/passes/collect_intra_doc_links.rs
+++ b/src/librustdoc/passes/collect_intra_doc_links.rs
@@ -333,7 +333,7 @@ impl ItemFragment {
                     FragmentKind::StructField => write!(s, "structfield.{}", name),
                     FragmentKind::Variant => write!(s, "variant.{}", name),
                     FragmentKind::VariantField => {
-                        let variant = tcx.item_name(tcx.parent(def_id).unwrap());
+                        let variant = tcx.item_name(tcx.parent(def_id));
                         write!(s, "variant.{}.field.{}", variant, name)
                     }
                 }
@@ -508,10 +508,10 @@ impl<'a, 'tcx> LinkCollector<'a, 'tcx> {
                 | DefKind::AssocTy
                 | DefKind::Variant
                 | DefKind::Field) => {
-                    let parent_def_id = tcx.parent(def_id).expect("nested item has no parent");
+                    let parent_def_id = tcx.parent(def_id);
                     if def_kind == DefKind::Field && tcx.def_kind(parent_def_id) == DefKind::Variant
                     {
-                        tcx.parent(parent_def_id).expect("variant has no parent")
+                        tcx.parent(parent_def_id)
                     } else {
                         parent_def_id
                     }
@@ -2333,14 +2333,10 @@ fn handle_variant(
     cx: &DocContext<'_>,
     res: Res,
 ) -> Result<(Res, Option<ItemFragment>), ErrorKind<'static>> {
-    cx.tcx
-        .parent(res.def_id(cx.tcx))
-        .map(|parent| {
-            let parent_def = Res::Def(DefKind::Enum, parent);
-            let variant = cx.tcx.expect_variant_res(res.as_hir_res().unwrap());
-            (parent_def, Some(ItemFragment(FragmentKind::Variant, variant.def_id)))
-        })
-        .ok_or_else(|| ResolutionFailure::NoParentItem.into())
+    let parent = cx.tcx.parent(res.def_id(cx.tcx));
+    let parent_def = Res::Def(DefKind::Enum, parent);
+    let variant = cx.tcx.expect_variant_res(res.as_hir_res().unwrap());
+    Ok((parent_def, Some(ItemFragment(FragmentKind::Variant, variant.def_id))))
 }
 
 /// Resolve a primitive type or value.
diff --git a/src/librustdoc/passes/collect_intra_doc_links/early.rs b/src/librustdoc/passes/collect_intra_doc_links/early.rs
index 68e10e3a18c..cd096c88003 100644
--- a/src/librustdoc/passes/collect_intra_doc_links/early.rs
+++ b/src/librustdoc/passes/collect_intra_doc_links/early.rs
@@ -188,7 +188,7 @@ impl EarlyDocLinkResolver<'_, '_> {
             return;
         }
         // FIXME: actually resolve links, not just add traits in scope.
-        if let Some(parent_id) = self.resolver.parent(scope_id) {
+        if let Some(parent_id) = self.resolver.opt_parent(scope_id) {
             self.add_traits_in_scope(parent_id);
         }
     }
@@ -253,7 +253,7 @@ impl EarlyDocLinkResolver<'_, '_> {
             {
                 if let Some(def_id) = child.res.opt_def_id() && !def_id.is_local() {
                     let scope_id = match child.res {
-                        Res::Def(DefKind::Variant, ..) => self.resolver.parent(def_id).unwrap(),
+                        Res::Def(DefKind::Variant, ..) => self.resolver.parent(def_id),
                         _ => def_id,
                     };
                     self.resolve_doc_links_extern_outer(def_id, scope_id); // Outer attribute scope
diff --git a/src/librustdoc/passes/collect_trait_impls.rs b/src/librustdoc/passes/collect_trait_impls.rs
index 9644e3d15fd..d245c3750ec 100644
--- a/src/librustdoc/passes/collect_trait_impls.rs
+++ b/src/librustdoc/passes/collect_trait_impls.rs
@@ -49,7 +49,7 @@ crate fn collect_trait_impls(mut krate: Crate, cx: &mut DocContext<'_>) -> Crate
         let _prof_timer = cx.tcx.sess.prof.generic_activity("build_local_trait_impls");
         let mut attr_buf = Vec::new();
         for &impl_def_id in all_trait_impls.iter().take_while(|def_id| def_id.is_local()) {
-            let mut parent = cx.tcx.parent(impl_def_id);
+            let mut parent = Some(cx.tcx.parent(impl_def_id));
             while let Some(did) = parent {
                 attr_buf.extend(
                     cx.tcx
@@ -65,7 +65,7 @@ crate fn collect_trait_impls(mut krate: Crate, cx: &mut DocContext<'_>) -> Crate
                         })
                         .cloned(),
                 );
-                parent = cx.tcx.parent(did);
+                parent = cx.tcx.opt_parent(did);
             }
             inline::build_impl(cx, None, impl_def_id, Some(&attr_buf), &mut new_items_local);
             attr_buf.clear();
diff --git a/src/tools/clippy/clippy_lints/src/matches/redundant_pattern_match.rs b/src/tools/clippy/clippy_lints/src/matches/redundant_pattern_match.rs
index 777ec9b75bc..aa3552001f4 100644
--- a/src/tools/clippy/clippy_lints/src/matches/redundant_pattern_match.rs
+++ b/src/tools/clippy/clippy_lints/src/matches/redundant_pattern_match.rs
@@ -193,7 +193,7 @@ fn find_sugg_for_if_let<'tcx>(
         PatKind::TupleStruct(ref qpath, [sub_pat], _) => {
             if let PatKind::Wild = sub_pat.kind {
                 let res = cx.typeck_results().qpath_res(qpath, check_pat.hir_id);
-                let Some(id) = res.opt_def_id().and_then(|ctor_id| cx.tcx.parent(ctor_id)) else { return };
+                let Some(id) = res.opt_def_id().map(|ctor_id| cx.tcx.parent(ctor_id)) else { return };
                 let lang_items = cx.tcx.lang_items();
                 if Some(id) == lang_items.result_ok_variant() {
                     ("is_ok()", try_get_generic_ty(op_ty, 0).unwrap_or(op_ty))
diff --git a/src/tools/clippy/clippy_lints/src/methods/bind_instead_of_map.rs b/src/tools/clippy/clippy_lints/src/methods/bind_instead_of_map.rs
index eec232e6d09..b88ec0963f2 100644
--- a/src/tools/clippy/clippy_lints/src/methods/bind_instead_of_map.rs
+++ b/src/tools/clippy/clippy_lints/src/methods/bind_instead_of_map.rs
@@ -42,7 +42,7 @@ pub(crate) trait BindInsteadOfMap {
 
     fn no_op_msg(cx: &LateContext<'_>) -> Option<String> {
         let variant_id = cx.tcx.lang_items().require(Self::VARIANT_LANG_ITEM).ok()?;
-        let item_id = cx.tcx.parent(variant_id)?;
+        let item_id = cx.tcx.parent(variant_id);
         Some(format!(
             "using `{}.{}({})`, which is a no-op",
             cx.tcx.item_name(item_id),
@@ -53,7 +53,7 @@ pub(crate) trait BindInsteadOfMap {
 
     fn lint_msg(cx: &LateContext<'_>) -> Option<String> {
         let variant_id = cx.tcx.lang_items().require(Self::VARIANT_LANG_ITEM).ok()?;
-        let item_id = cx.tcx.parent(variant_id)?;
+        let item_id = cx.tcx.parent(variant_id);
         Some(format!(
             "using `{}.{}(|x| {}(y))`, which is more succinctly expressed as `{}(|x| y)`",
             cx.tcx.item_name(item_id),
@@ -145,7 +145,7 @@ pub(crate) trait BindInsteadOfMap {
         if_chain! {
             if let Some(adt) = cx.typeck_results().expr_ty(recv).ty_adt_def();
             if let Ok(vid) = cx.tcx.lang_items().require(Self::VARIANT_LANG_ITEM);
-            if Some(adt.did()) == cx.tcx.parent(vid);
+            if adt.did() == cx.tcx.parent(vid);
             then {} else { return false; }
         }
 
@@ -182,7 +182,7 @@ pub(crate) trait BindInsteadOfMap {
     fn is_variant(cx: &LateContext<'_>, res: Res) -> bool {
         if let Res::Def(DefKind::Ctor(CtorOf::Variant, CtorKind::Fn), id) = res {
             if let Ok(variant_id) = cx.tcx.lang_items().require(Self::VARIANT_LANG_ITEM) {
-                return cx.tcx.parent(id) == Some(variant_id);
+                return cx.tcx.parent(id) == variant_id;
             }
         }
         false
diff --git a/src/tools/clippy/clippy_lints/src/methods/chars_cmp.rs b/src/tools/clippy/clippy_lints/src/methods/chars_cmp.rs
index 2cf2c5641bf..f7b79f0839b 100644
--- a/src/tools/clippy/clippy_lints/src/methods/chars_cmp.rs
+++ b/src/tools/clippy/clippy_lints/src/methods/chars_cmp.rs
@@ -19,7 +19,7 @@ pub(super) fn check(
     if_chain! {
         if let Some(args) = method_chain_args(info.chain, chain_methods);
         if let hir::ExprKind::Call(fun, [arg_char]) = info.other.kind;
-        if let Some(id) = path_def_id(cx, fun).and_then(|ctor_id| cx.tcx.parent(ctor_id));
+        if let Some(id) = path_def_id(cx, fun).map(|ctor_id| cx.tcx.parent(ctor_id));
         if Some(id) == cx.tcx.lang_items().option_some_variant();
         then {
             let mut applicability = Applicability::MachineApplicable;
diff --git a/src/tools/clippy/clippy_lints/src/methods/option_map_or_none.rs b/src/tools/clippy/clippy_lints/src/methods/option_map_or_none.rs
index 2a5ab6e625c..76bc9466ed8 100644
--- a/src/tools/clippy/clippy_lints/src/methods/option_map_or_none.rs
+++ b/src/tools/clippy/clippy_lints/src/methods/option_map_or_none.rs
@@ -75,7 +75,7 @@ pub(super) fn check<'tcx>(
             let arg_snippet = snippet(cx, span, "..");
             let body = cx.tcx.hir().body(id);
                 if let Some((func, [arg_char])) = reduce_unit_expression(&body.value);
-                if let Some(id) = path_def_id(cx, func).and_then(|ctor_id| cx.tcx.parent(ctor_id));
+                if let Some(id) = path_def_id(cx, func).map(|ctor_id| cx.tcx.parent(ctor_id));
                 if Some(id) == cx.tcx.lang_items().option_some_variant();
                 then {
                     let func_snippet = snippet(cx, arg_char.span, "..");
diff --git a/src/tools/clippy/clippy_lints/src/missing_doc.rs b/src/tools/clippy/clippy_lints/src/missing_doc.rs
index 5816a95dceb..a20377f320b 100644
--- a/src/tools/clippy/clippy_lints/src/missing_doc.rs
+++ b/src/tools/clippy/clippy_lints/src/missing_doc.rs
@@ -114,7 +114,7 @@ impl<'tcx> LateLintPass<'tcx> for MissingDoc {
             hir::ItemKind::Fn(..) => {
                 // ignore main()
                 if it.ident.name == sym::main {
-                    let at_root = cx.tcx.local_parent(it.def_id) == Some(CRATE_DEF_ID);
+                    let at_root = cx.tcx.local_parent(it.def_id) == CRATE_DEF_ID;
                     if at_root {
                         return;
                     }
diff --git a/src/tools/clippy/clippy_utils/src/lib.rs b/src/tools/clippy/clippy_utils/src/lib.rs
index 74978720424..7d46952d971 100644
--- a/src/tools/clippy/clippy_utils/src/lib.rs
+++ b/src/tools/clippy/clippy_utils/src/lib.rs
@@ -235,7 +235,7 @@ pub fn is_lang_ctor(cx: &LateContext<'_>, qpath: &QPath<'_>, lang_item: LangItem
     if let QPath::Resolved(_, path) = qpath {
         if let Res::Def(DefKind::Ctor(..), ctor_id) = path.res {
             if let Ok(item_id) = cx.tcx.lang_items().require(lang_item) {
-                return cx.tcx.parent(ctor_id) == Some(item_id);
+                return cx.tcx.parent(ctor_id) == item_id;
             }
         }
     }