From bc9a96ef9eeab89276d67929f4a8a7d88f5dbc02 Mon Sep 17 00:00:00 2001

From: Stephan Hartmann <stha09@googlemail.com>

Date: Wed, 27 May 2020 13:37:25 +0000

Subject: [PATCH] GCC: fix template specialization in TraceInCollectionTrait

GCC complains that explicit specialization in non-namespace scope

is happening for TraceImpl. Move TraceImpl implementations into

different nested classes and select implementation using

std::conditional.

Bug: 819294

Change-Id: I8feea5f2aa6e1f87daad61f496d6b53b1bbc49ac

Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2217887

Reviewed-by: Michael Lippautz <mlippautz@chromium.org>

Commit-Queue: Michael Lippautz <mlippautz@chromium.org>

Cr-Commit-Position: refs/heads/master@{#772215}

---

diff --git a/third_party/blink/renderer/platform/heap/collection_support/heap_hash_table_backing.h b/third_party/blink/renderer/platform/heap/collection_support/heap_hash_table_backing.h

index 31e7888..2c0583f 100644

--- a/third_party/blink/renderer/platform/heap/collection_support/heap_hash_table_backing.h

+++ b/third_party/blink/renderer/platform/heap/collection_support/heap_hash_table_backing.h

@@ -241,50 +241,52 @@

   static void Trace(blink::Visitor* visitor,

                     const KeyValuePair<Key, Value>& self) {

-    TraceImpl(visitor, self);

+    TraceImpl::Trace(visitor, self);

   }

  private:

-  template <bool = EphemeronHelper::is_ephemeron>

-  static void TraceImpl(blink::Visitor* visitor,

-                        const KeyValuePair<Key, Value>& self);

-

-  // Strongification of ephemerons, i.e., Weak/Strong and Strong/Weak.

-  template <>

-  static void TraceImpl<true>(blink::Visitor* visitor,

-                              const KeyValuePair<Key, Value>& self) {

+  struct TraceImplEphemerons {

     // Strongification of ephemerons, i.e., Weak/Strong and Strong/Weak.

-    // The helper ensures that helper.key always refers to the weak part and

-    // helper.value always refers to the dependent part.

-    // We distinguish ephemeron from Weak/Weak and Strong/Strong to allow users

-    // to override visitation behavior. An example is creating a heap snapshot,

-    // where it is useful to annotate values as being kept alive from keys

-    // rather than the table.

-    EphemeronHelper helper(&self.key, &self.value);

-    // Strongify the weak part.

-    blink::TraceCollectionIfEnabled<

-        kNoWeakHandling, typename EphemeronHelper::KeyType,

-        typename EphemeronHelper::KeyTraits>::Trace(visitor, helper.key);

-    // Strongify the dependent part.

-    visitor->TraceEphemeron(

-        *helper.key, helper.value,

-        blink::TraceCollectionIfEnabled<

-            kNoWeakHandling, typename EphemeronHelper::ValueType,

-            typename EphemeronHelper::ValueTraits>::Trace);

-  }

+    static void Trace(blink::Visitor* visitor,

+                      const KeyValuePair<Key, Value>& self) {

+      // Strongification of ephemerons, i.e., Weak/Strong and Strong/Weak.

+      // The helper ensures that helper.key always refers to the weak part and

+      // helper.value always refers to the dependent part.

+      // We distinguish ephemeron from Weak/Weak and Strong/Strong to allow

+      // users to override visitation behavior. An example is creating a heap

+      // snapshot, where it is useful to annotate values as being kept alive

+      // from keys rather than the table.

+      EphemeronHelper helper(&self.key, &self.value);

+      // Strongify the weak part.

+      blink::TraceCollectionIfEnabled<

+          kNoWeakHandling, typename EphemeronHelper::KeyType,

+          typename EphemeronHelper::KeyTraits>::Trace(visitor, helper.key);

+      // Strongify the dependent part.

+      visitor->TraceEphemeron(

+          *helper.key, helper.value,

+          blink::TraceCollectionIfEnabled<

+              kNoWeakHandling, typename EphemeronHelper::ValueType,

+              typename EphemeronHelper::ValueTraits>::Trace);

+    }

+  };

-  template <>

-  static void TraceImpl<false>(blink::Visitor* visitor,

-                               const KeyValuePair<Key, Value>& self) {

-    // Strongification of non-ephemeron KVP, i.e., Strong/Strong or Weak/Weak.

-    // Order does not matter here.

-    blink::TraceCollectionIfEnabled<

-        kNoWeakHandling, Key, typename Traits::KeyTraits>::Trace(visitor,

-                                                                 &self.key);

-    blink::TraceCollectionIfEnabled<

-        kNoWeakHandling, Value,

-        typename Traits::ValueTraits>::Trace(visitor, &self.value);

-  }

+  struct TraceImplDefault {

+    static void Trace(blink::Visitor* visitor,

+                      const KeyValuePair<Key, Value>& self) {

+      // Strongification of non-ephemeron KVP, i.e., Strong/Strong or Weak/Weak.

+      // Order does not matter here.

+      blink::TraceCollectionIfEnabled<

+          kNoWeakHandling, Key, typename Traits::KeyTraits>::Trace(visitor,

+                                                                   &self.key);

+      blink::TraceCollectionIfEnabled<

+          kNoWeakHandling, Value,

+          typename Traits::ValueTraits>::Trace(visitor, &self.value);

+    }

+  };

+

+  using TraceImpl = typename std::conditional

+                                              TraceImplEphemerons,

+                                              TraceImplDefault>::type;

 };

 template <typename Key, typename Value, typename Traits>