From 0b35940a72aaa4575e4dd1f8991abb037bc2a0ed Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Wed, 1 Jun 2022 15:10:19 -0600
Subject: [PATCH] Make hb::shared_ptr hashable

---
 src/hb-algs.hh      | 16 +++++++++++-----
 src/hb-cplusplus.hh |  1 +
 src/test-map.cc     |  9 +++++++++
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/src/hb-algs.hh b/src/hb-algs.hh
index 6ffe0e22e..c5fa0bcbc 100644
--- a/src/hb-algs.hh
+++ b/src/hb-algs.hh
@@ -246,12 +246,18 @@ struct
   impl (const T& v, hb_priority<1>) const HB_RETURN (uint32_t, std::hash<hb_decay<decltype (hb_deref (v))>>{} (hb_deref (v)))
 
   template <typename T,
-	    hb_enable_if (std::is_integral<T>::value)> constexpr auto
-  impl (const T& v, hb_priority<0>) const HB_AUTO_RETURN
-  (
+	    hb_enable_if (std::is_integral<T>::value)> constexpr uint32_t
+  impl (const T& v, hb_priority<0>) const
+  {
     /* Knuth's multiplicative method: */
-    (uint32_t) v * 2654435761u
-  )
+    return (uint32_t) v * 2654435761u;
+  }
+
+  template <typename T> constexpr uint32_t
+  impl (const hb::shared_ptr<T>& v, hb_priority<0>) const
+  {
+    return (uint32_t) (intptr_t) v.get () * 2654435761u;
+  }
 
   public:
 
diff --git a/src/hb-cplusplus.hh b/src/hb-cplusplus.hh
index 122c6920e..39b150fea 100644
--- a/src/hb-cplusplus.hh
+++ b/src/hb-cplusplus.hh
@@ -51,6 +51,7 @@ struct shared_ptr
 {
   using v = vtable<T>;
 
+  shared_ptr (std::nullptr_t) : p (nullptr) {}
   explicit shared_ptr (T *p = nullptr) : p (p) {}
   shared_ptr (const shared_ptr &o) : p (v::reference (o.p)) {}
   shared_ptr (shared_ptr &&o) : p (o.p) { o.p = nullptr; }
diff --git a/src/test-map.cc b/src/test-map.cc
index 3f81e8c3a..7d437a9cc 100644
--- a/src/test-map.cc
+++ b/src/test-map.cc
@@ -222,5 +222,14 @@ main (int argc, char **argv)
     assert (m2.get (vector_t {1}) == vector_t {2});
   }
 
+  /* Test hb::shared_ptr. */
+  {
+    hb_hashmap_t<hb::shared_ptr<hb_set_t>, hb::shared_ptr<hb_set_t>, std::nullptr_t, std::nullptr_t, nullptr, nullptr> m;
+
+    hb_hash (hb::shared_ptr<hb_set_t> ());
+    m.get (hb::shared_ptr<hb_set_t> ());
+    m.get (hb::shared_ptr<hb_set_t> (hb_set_get_empty ()));
+  }
+
   return 0;
 }