Export globals and make them weak on static builds so they work acros…

…s SOs.

doc/corrade-changelog.dox

@@ -152,6 +152,12 @@ namespace Corrade {
 
 @subsection corrade-changelog-latest-changes Changes and improvements
 
+-   Global state used by @ref PluginManager::Manager, @ref Utility::Debug and
+    @ref Utility::Resource internals is no longer duplicated when Corrade is
+    built statically and linked to more than one dynamic library or executable.
+    Currently that holds only for Linux and macOS, Windows support will come
+    next.
+
 @subsubsection corrade-changelog-latest-changes-containers Containers library
 
 -   It's now possible to create @ref Containers::ScopeGuard without a handle

src/Corrade/PluginManager/AbstractManager.cpp

@@ -131,9 +131,12 @@ struct AbstractManager::State {
 
 const int AbstractManager::Version = CORRADE_PLUGIN_VERSION;
 
+#ifndef CORRADE_BUILD_STATIC
+/* (Of course) can't be in an unnamed namespace in order to export it below */
 namespace {
+#endif
 
-struct {
+struct Globals {
     /* A linked list of static plugins. Managed using utilities from
        Containers/Implementation/RawForwardList.h, look there for more info. */
     Implementation::StaticPlugin* staticPlugins;
@@ -147,17 +150,33 @@ struct {
        errors because std::pair is trying to copy itself. So calm down and
        ignore those few delete calls. Please. Last tried: March 2018. */
     std::map<std::string, AbstractManager::Plugin*>* plugins;
+};
 
+#if defined(CORRADE_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS)
+/* On static builds that get linked to multiple shared libraries and then used
+   in a single app we want to ensure there's just one global symbol. On Linux
+   it's apparently enough to just export, macOS needs the weak attribute.
+   Windows not handled yet, as it needs a workaround using DllMain() and
+   GetProcAddress(). */
+CORRADE_VISIBILITY_EXPORT
+    #ifdef __GNUC__
+    __attribute__((weak))
+    #else
+    /* uh oh? the test will fail, probably */
+    #endif
+#endif
 /* The value of this variable is guaranteed to be zero-filled even before any
    static plugin initializers are executed, which means we don't hit any static
    initialization order fiasco. */
-} globals{nullptr, nullptr};
+Globals globals{nullptr, nullptr};
+
+#ifndef CORRADE_BUILD_STATIC
+}
+#endif
 
 static_assert(std::is_pod<Implementation::StaticPlugin>::value,
     "static plugins shouldn't cause any global initialization / finalization to happen on their own");
 
-}
-
 #ifndef DOXYGEN_GENERATING_OUTPUT
 void AbstractManager::importStaticPlugin(int version, Implementation::StaticPlugin& plugin) {
     CORRADE_ASSERT(version == Version,

src/Corrade/Utility/Debug.cpp

@@ -76,23 +76,47 @@ HANDLE streamOutputHandle(const std::ostream* s) {
 }
 #endif
 
-#ifdef CORRADE_BUILD_MULTITHREADED
-CORRADE_THREAD_LOCAL
+}
+
+#ifndef CORRADE_BUILD_STATIC
+/* (Of course) can't be in an unnamed namespace in order to export it below */
+namespace {
 #endif
-struct {
+
+struct DebugGlobals {
     std::ostream *output, *warningOutput, *errorOutput;
     #if !defined(CORRADE_TARGET_WINDOWS) ||defined(CORRADE_UTILITY_USE_ANSI_COLORS)
     Debug::Color color;
     bool colorBold;
     #endif
-} debugGlobals {
+};
+
+#ifdef CORRADE_BUILD_MULTITHREADED
+CORRADE_THREAD_LOCAL
+#endif
+#if defined(CORRADE_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS)
+/* On static builds that get linked to multiple shared libraries and then used
+   in a single app we want to ensure there's just one global symbol. On Linux
+   it's apparently enough to just export, macOS needs the weak attribute.
+   Windows not handled yet, as it needs a workaround using DllMain() and
+   GetProcAddress(). */
+CORRADE_VISIBILITY_EXPORT
+    #ifdef __GNUC__
+    __attribute__((weak))
+    #else
+    /* uh oh? the test will fail, probably */
+    #endif
+#endif
+DebugGlobals debugGlobals{
     &std::cout, &std::cerr, &std::cerr,
     #if !defined(CORRADE_TARGET_WINDOWS) ||defined(CORRADE_UTILITY_USE_ANSI_COLORS)
     Debug::Color::Default, false
     #endif
 };
 
+#ifndef CORRADE_BUILD_STATIC
 }
+#endif
 
 template<Debug::Color c, bool bold> Debug::Modifier Debug::colorInternal() {
     return [](Debug& debug) {

src/Corrade/Utility/Resource.cpp

@@ -45,9 +45,12 @@
 
 namespace Corrade { namespace Utility {
 
+#ifndef CORRADE_BUILD_STATIC
+/* (Of course) can't be in an unnamed namespace in order to export it below */
 namespace {
+#endif
 
-struct {
+struct ResourceGlobals {
     /* A linked list of resources. Managed using utilities from
        Containers/Implementation/RawForwardList.h, look there for more info. */
     Implementation::ResourceGroup* groups;
@@ -56,13 +59,29 @@ struct {
        Resource::overrideGroup() and stores a pointer to a function-local
        static variable from there. */
     std::map<std::string, std::string>* overrideGroups;
+};
 
+#if defined(CORRADE_BUILD_STATIC) && !defined(CORRADE_TARGET_WINDOWS)
+/* On static builds that get linked to multiple shared libraries and then used
+   in a single app we want to ensure there's just one global symbol. On Linux
+   it's apparently enough to just export, macOS needs the weak attribute.
+   Windows not handled yet, as it needs a workaround using DllMain() and
+   GetProcAddress(). */
+CORRADE_VISIBILITY_EXPORT
+    #ifdef __GNUC__
+    __attribute__((weak))
+    #else
+    /* uh oh? the test will fail, probably */
+    #endif
+#endif
 /* The value of this variable is guaranteed to be zero-filled even before any
    resource initializers are executed, which means we don't hit any static
    initialization order fiasco. */
-} resourceGlobals{nullptr, nullptr};
+ResourceGlobals resourceGlobals{nullptr, nullptr};
 
+#ifndef CORRADE_BUILD_STATIC
 }
+#endif
 
 struct Resource::OverrideData {
     const Configuration conf;