Make it easier to use resources in plugins when using static linking

RCC generates code that registers resources automatically on program
startup via global constructors. When linking statically and nothing
references the symbols in the .o file compiled from the RCC generated
code, then the linker will discard the embedded resources and they will
not get initialized. That is why for static linking it is necessary to
explicitly initialize resources using the Q_INIT_RESOURCE macro.

We can avoid the need for the explicit initialization in the context of
plugins that are statically linked into the application. resources.prf
can generate a .cpp file with a helper function that contains all the
Q_INIT_RESOURCE calls for all resources in the plugin. That helper
function in turn is injected into the plugin entry point, which in turn
is guaranteed to be included in the final binary.

Change-Id: If1abf9c85ef92935020af073b989c58c1ae6ca63
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/mkspecs/features/resources.prf b/mkspecs/features/resources.prf
index ff45446219..7ae78d021e 100644
--- a/mkspecs/features/resources.prf
+++ b/mkspecs/features/resources.prf
@@ -72,6 +72,38 @@ for(resource, RESOURCES) {
     RESOURCES += $$resource_file
 }
 
+!isEmpty(RESOURCES):contains(TEMPLATE, .*lib):plugin:static {
+    resource_init_function = $$lower($$basename(TARGET))_plugin_resource_init
+    DEFINES += "QT_PLUGIN_RESOURCE_INIT_FUNCTION=$$resource_init_function"
+
+    RESOURCE_INIT_CPP = $$OUT_PWD/$$lower($$basename(TARGET))_plugin_resources.cpp
+
+    GENERATED_SOURCES += $$RESOURCE_INIT_CPP
+    QMAKE_DISTCLEAN += $$RESOURCE_INIT_CPP
+
+    !build_pass {
+        RESOURCE_INIT_CONT = \
+            "// This file is autogenerated by qmake. It contains a function that" \
+            "// references all resources the plugin includes and the function is" \
+            "// referenced by Qt_(MOC_)EXPORT_PLUGIN to ensure the inclusion in" \
+            "// the statically linked plugin." \
+            "$${LITERAL_HASH}include <QtCore/qglobal.h>" \
+            "void $${resource_init_function}() " \
+            "{" \
+
+        for (resource, RESOURCES) {
+            resource_name = $$section($$list($$basename(resource)), ., 0, 0)
+            resource_name = $$replace(resource_name, [^a-zA-Z0-9_], _)
+            RESOURCE_INIT_CONT += "    Q_INIT_RESOURCE($$resource_name);"
+        }
+
+        RESOURCE_INIT_CONT += \
+            "}"
+
+        write_file($$RESOURCE_INIT_CPP, RESOURCE_INIT_CONT)|error()
+    }
+}
+
 rcc.input = RESOURCES
 rcc.name = RCC ${QMAKE_FILE_IN}
 rcc.depend_command = $$QMAKE_RCC_DEP -list $$QMAKE_RESOURCE_FLAGS ${QMAKE_FILE_IN}