Bug 1734858, use the real index when updating the index after a bfcache load, r=peterv

The issue is that when going back from a non-bfcacheable page to a bfcacheable page and the first page
modifies requested index around the same time, UpdateIndex() doesn't have the right requested index. This is a variant of bug 1725680.
The test case loads a non-bfcacheable page, then bfcachable, then another non-bfcacheable and then goes back and forward.
Without the patch indexes go wrong and forward doesn't do anything.

Differential Revision: https://phabricator.services.mozilla.com/D127963

docshell/shistory/nsSHistory.cpp

@@ -1202,9 +1202,14 @@ static void FinishRestore(CanonicalBrowsingContext* aBrowsingContext,
 
   aEntry->SetFrameLoader(nullptr);
 
+  nsCOMPtr<nsISHistory> shistory = aEntry->GetShistory();
+  int32_t indexOfHistoryLoad =
+      shistory ? shistory->GetIndexOfEntry(aEntry) : -1;
+
   nsCOMPtr<nsFrameLoaderOwner> frameLoaderOwner =
       do_QueryInterface(aBrowsingContext->GetEmbedderElement());
-  if (frameLoaderOwner && aFrameLoader->GetMaybePendingBrowsingContext()) {
+  if (frameLoaderOwner && aFrameLoader->GetMaybePendingBrowsingContext() &&
+      indexOfHistoryLoad >= 0) {
     // Synthesize a STATE_START WebProgress state change event from here
     // in order to ensure emitting it on the BrowsingContext we navigate *from*
     // instead of the BrowsingContext we navigate *to*.
@@ -1255,7 +1260,8 @@ static void FinishRestore(CanonicalBrowsingContext* aBrowsingContext,
 
     // Assuming we still have the session history, update the index.
     if (loadingBC->GetSessionHistory()) {
-      loadingBC->GetSessionHistory()->UpdateIndex();
+      shistory->InternalSetRequestedIndex(indexOfHistoryLoad);
+      shistory->UpdateIndex();
     }
     loadingBC->HistoryCommitIndexAndLength();
     Unused << loadingBC->SetIsInBFCache(false);

docshell/test/navigation/file_new_shentry_during_history_navigation_3.html

@@ -0,0 +1,22 @@
+<script>
+  window.onpageshow = function(e) {
+    if (location.search == "?v2") {
+      onbeforeunload = function() {
+        history.pushState("data1", "", "?push1");
+      }
+    }
+
+    let bc = new BroadcastChannel("new_shentry_during_history_navigation");
+    bc.onmessage = function(event) {
+      bc.close();
+      if (event.data == "loadnext") {
+        location.href = "file_new_shentry_during_history_navigation_4.html";
+      } else if (event.data == "back") {
+        history.back();
+      } else if (event.data == "close") {
+        window.close();
+      }
+    }
+    bc.postMessage({page: location.href, type: e.type, persisted: e.persisted});
+  }
+</script>

docshell/test/navigation/file_new_shentry_during_history_navigation_3.html^headers^

@@ -0,0 +1 @@
+Cache-control: no-store

docshell/test/navigation/file_new_shentry_during_history_navigation_4.html

@@ -0,0 +1,16 @@
+<script>
+  window.onpageshow = function(e) {
+    let bc = new BroadcastChannel("new_shentry_during_history_navigation");
+    bc.onmessage = function(event) {
+      bc.close();
+      if (event.data == "loadnext") {
+        location.href = "file_new_shentry_during_history_navigation_3.html?v2";
+      } else if (event.data == "forward") {
+        history.forward();
+      } else if (event.data == "close") {
+        window.close();
+      }
+    }
+    bc.postMessage({page: location.href, type: e.type, persisted: e.persisted});
+  }
+</script>

docshell/test/navigation/mochitest.ini

@@ -133,6 +133,9 @@ support-files =
   file_new_shentry_during_history_navigation_1.html^headers^
   file_new_shentry_during_history_navigation_2.html
   file_new_shentry_during_history_navigation_2.html^headers^
+  file_new_shentry_during_history_navigation_3.html
+  file_new_shentry_during_history_navigation_3.html^headers^
+  file_new_shentry_during_history_navigation_4.html
 [test_not-opener.html]
 [test_online_offline_bfcache.html]
 support-files = file_online_offline_bfcache.html

docshell/test/navigation/test_new_shentry_during_history_navigation.html

@@ -43,13 +43,43 @@
       setTimeout(function() {
           win.onmessage = null;
           win.close();
-          SimpleTest.finish();
+          testBfcache();
       }, 500);
       window.onmessage = function(event) {
         ok(false, "Should not get a message " + event.data);
       }
     }
 
+    async function testBfcache() {
+      let bc = new BroadcastChannel("new_shentry_during_history_navigation");
+      let pageshowCount = 0;
+      bc.onmessage = function(event) {
+        if (event.data.type == "pageshow") {
+          ++pageshowCount;
+          info("pageshow: " + pageshowCount + ", page: " + event.data.page);
+          if (pageshowCount == 1) {
+            ok(!event.data.persisted, "The page should not be bfcached.");
+            bc.postMessage("loadnext");
+          } else if (pageshowCount == 2) {
+            ok(!event.data.persisted, "The page should not be bfcached.");
+            bc.postMessage("loadnext");
+          } else if (pageshowCount == 3) {
+            ok(!event.data.persisted, "The page should not be bfcached.");
+            bc.postMessage("back");
+          } else if (pageshowCount == 4) {
+            ok(event.data.persisted, "The page should be bfcached.");
+            bc.postMessage("forward");
+          } else if (pageshowCount == 5) {
+            ok(event.data.page.includes("v2"), "Should have gone forward.");
+            bc.postMessage("close");
+            SimpleTest.finish();
+          }
+        }
+      };
+      win = window.open("file_new_shentry_during_history_navigation_3.html", "", "noopener");
+
+    }
+
   </script>
 </head>
 <body onload="test()">