Reduce HIR debug output

HIR debug output is currently very verbose, especially when used with
the alternate (`#`) flag. This commit reduces the amount of noisy
newlines by forcing a few small key types to stay on one line, which
makes the output easier to read and scroll by.

```
$ rustc +after hello_world.rs -Zunpretty=hir-tree | wc -l
582
$ rustc +before hello_world.rs -Zunpretty=hir-tree | wc -l
932
```

compiler/rustc_data_structures/src/sorted_map.rs

@@ -1,6 +1,7 @@
 use crate::stable_hasher::{HashStable, StableHasher, StableOrd};
 use std::borrow::Borrow;
 use std::cmp::Ordering;
+use std::fmt::Debug;
 use std::mem;
 use std::ops::{Bound, Index, IndexMut, RangeBounds};
 
@@ -16,7 +17,7 @@ pub use index_map::SortedIndexMultiMap;
 /// stores data in a more compact way. It also supports accessing contiguous
 /// ranges of elements as a slice, and slices of already sorted elements can be
 /// inserted efficiently.
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)]
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
 pub struct SortedMap<K, V> {
     data: Vec<(K, V)>,
 }
@@ -314,5 +315,11 @@ impl<K: HashStable<CTX> + StableOrd, V: HashStable<CTX>, CTX> HashStable<CTX> fo
     }
 }
 
+impl<K: Debug, V: Debug> Debug for SortedMap<K, V> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_map().entries(self.data.iter().map(|(a, b)| (a, b))).finish()
+    }
+}
+
 #[cfg(test)]
 mod tests;

compiler/rustc_hir/src/hir.rs

@@ -854,7 +854,11 @@ impl fmt::Debug for OwnerNodes<'_> {
                 &self
                     .nodes
                     .iter_enumerated()
-                    .map(|(id, parented_node)| (id, parented_node.as_ref().map(|node| node.parent)))
+                    .map(|(id, parented_node)| {
+                        let parented_node = parented_node.as_ref().map(|node| node.parent);
+
+                        debug_fn(move |f| write!(f, "({id:?}, {parented_node:?})"))
+                    })
                     .collect::<Vec<_>>(),
             )
             .field("bodies", &self.bodies)
@@ -3615,3 +3619,13 @@ mod size_asserts {
     static_assert_size!(TyKind<'_>, 32);
     // tidy-alphabetical-end
 }
+
+fn debug_fn(f: impl Fn(&mut fmt::Formatter<'_>) -> fmt::Result) -> impl fmt::Debug {
+    struct DebugFn<F>(F);
+    impl<F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result> fmt::Debug for DebugFn<F> {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            (self.0)(fmt)
+        }
+    }
+    DebugFn(f)
+}

compiler/rustc_hir/src/hir_id.rs

@@ -1,14 +1,21 @@
 use crate::def_id::{DefId, DefIndex, LocalDefId, CRATE_DEF_ID};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, StableOrd, ToStableHashKey};
 use rustc_span::{def_id::DefPathHash, HashStableContext};
-use std::fmt;
+use std::fmt::{self, Debug};
 
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
 #[derive(Encodable, Decodable)]
 pub struct OwnerId {
     pub def_id: LocalDefId,
 }
 
+impl Debug for OwnerId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Example: DefId(0:1 ~ aa[7697]::{use#0})
+        Debug::fmt(&self.def_id, f)
+    }
+}
+
 impl From<OwnerId> for HirId {
     fn from(owner: OwnerId) -> HirId {
         HirId { owner, local_id: ItemLocalId::from_u32(0) }
@@ -60,14 +67,22 @@ impl<CTX: HashStableContext> ToStableHashKey<CTX> for OwnerId {
 /// the `local_id` part of the `HirId` changing, which is a very useful property in
 /// incremental compilation where we have to persist things through changes to
 /// the code base.
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
 #[derive(Encodable, Decodable, HashStable_Generic)]
 #[rustc_pass_by_value]
 pub struct HirId {
     pub owner: OwnerId,
     pub local_id: ItemLocalId,
 }
 
+impl Debug for HirId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Example: HirId(DefId(0:1 ~ aa[7697]::{use#0}).10)
+        // Don't use debug_tuple to always keep this on one line.
+        write!(f, "HirId({:?}.{:?})", self.owner, self.local_id)
+    }
+}
+
 impl HirId {
     /// Signal local id which should never be used.
     pub const INVALID: HirId =

src/test/ui/thir-tree.stdout

@@ -32,12 +32,7 @@ Thir {
             kind: Scope {
                 region_scope: Node(2),
                 lint_level: Explicit(
-                    HirId {
-                        owner: OwnerId {
-                            def_id: DefId(0:3 ~ thir_tree[8f1d]::main),
-                        },
-                        local_id: 2,
-                    },
+                    HirId(DefId(0:3 ~ thir_tree[8f1d]::main).2),
                 ),
                 value: e0,
             },