From b57462d60dbebedcfac00544d5ff1592c5117c1f Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Mon, 5 Apr 2021 17:07:53 +0200
Subject: `Interned<T>`: Only hash the pointer

---
 crates/hir_def/src/intern.rs | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/crates/hir_def/src/intern.rs b/crates/hir_def/src/intern.rs
index 0d5419be5..abc304ef0 100644
--- a/crates/hir_def/src/intern.rs
+++ b/crates/hir_def/src/intern.rs
@@ -5,7 +5,7 @@
 use std::{
     collections::HashMap,
     fmt::{self, Debug},
-    hash::{BuildHasherDefault, Hash},
+    hash::{BuildHasherDefault, Hash, Hasher},
     ops::Deref,
     sync::Arc,
 };
@@ -20,7 +20,6 @@ type InternMap<T> = DashMap<Arc<T>, (), BuildHasherDefault<FxHasher>>;
 type Guard<T> =
     RwLockWriteGuard<'static, HashMap<Arc<T>, SharedValue<()>, BuildHasherDefault<FxHasher>>>;
 
-#[derive(Hash)]
 pub struct Interned<T: Internable + ?Sized> {
     arc: Arc<T>,
 }
@@ -137,6 +136,13 @@ impl PartialEq for Interned<str> {
 
 impl Eq for Interned<str> {}
 
+impl<T: Internable + ?Sized> Hash for Interned<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        // NOTE: Cast disposes vtable pointer / slice/str length.
+        state.write_usize(Arc::as_ptr(&self.arc) as *const () as usize)
+    }
+}
+
 impl<T: Internable + ?Sized> AsRef<T> for Interned<T> {
     #[inline]
     fn as_ref(&self) -> &T {
-- 
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