Bug 1706452 - Reintroduce a mozgtk library after bug 1377445. r=firefox-build-system-reviewers,rmader,mhentges

Differential Revision: https://phabricator.services.mozilla.com/D112883

browser/installer/package-manifest.in

@@ -104,6 +104,7 @@
 #endif
 #endif
 #ifdef MOZ_GTK
+@BINPATH@/@DLL_PREFIX@mozgtk@DLL_SUFFIX@
 #ifdef MOZ_WAYLAND
 @BINPATH@/@DLL_PREFIX@mozwayland@DLL_SUFFIX@
 #endif

toolkit/library/moz.build

@@ -157,6 +157,21 @@ USE_LIBS += [
 ]
 
 if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
+    # The mozgtk library is a workaround that makes Gtk+ use libwayland-client
+    # instead of mozwayland. The reason it works is that by being a dependency
+    # of libxul, mozgtk appears in dependentlibs.list, preceding mozwayland
+    # (which is important and guaranteed by the USE_LIBS order in this file).
+    # That, in turn, makes firefox dlopen() mozgtk before mozwayland, which
+    # will trigger the loading of the Gtk+ libraries (mozgtk depending on them).
+    # Those libraries, if they depend on libwayland-client, will use the symbols
+    # from libwayland-client because mozwayland is not loaded yet.
+    # When eventually libxul is loaded after both mozgtk and mozwayland, it will
+    # get symbols from libwayland-client too.
+    # In the case where Gtk+ doesn't have wayland support, libwayland-client is
+    # not loaded, and libxul ends up using the mozwayland symbols.
+    USE_LIBS += [
+        "mozgtk",
+    ]
     OS_LIBS += CONFIG["MOZ_GTK3_LIBS"]
 
 if CONFIG["MOZ_WAYLAND"]:

widget/gtk/moz.build

@@ -19,6 +19,9 @@ with Files("*IMContextWrapper*"):
 with Files("*nsGtkKeyUtils*"):
     BUG_COMPONENT = ("Core", "DOM: UI Events & Focus Handling")
 
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
+    DIRS += ["mozgtk"]
+
 if CONFIG["MOZ_WAYLAND"]:
     DIRS += ["wayland", "mozwayland"]
 

widget/gtk/mozgtk/moz.build

@@ -0,0 +1,30 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+SharedLibrary("mozgtk")
+
+# If LDFLAGS contains -Wl,--as-needed or if it's the default for the toolchain,
+# we need to add -Wl,--no-as-needed before the gtk libraries, otherwise the
+# linker will drop those dependencies because no symbols are used from them.
+# But those dependencies need to be kept for things to work properly.
+# Ideally, we'd only add -Wl,--no-as-needed if necessary, but it's just simpler
+# to add it unconditionally. This library is also simple enough that forcing
+# -Wl,--as-needed after the gtk libraries is not going to make a significant
+# difference.
+if CONFIG["GCC_USE_GNU_LD"]:
+    no_as_needed = ["-Wl,--no-as-needed"]
+    as_needed = ["-Wl,--as-needed"]
+else:
+    no_as_needed = []
+    as_needed = []
+
+OS_LIBS += [f for f in CONFIG["MOZ_GTK3_LIBS"] if f.startswith("-L")]
+OS_LIBS += no_as_needed
+OS_LIBS += [
+    "gtk-3",
+    "gdk-3",
+]
+OS_LIBS += as_needed