PluginManager: Provide helpful output if unit tests cannot be run

We can show the errors directly, rather than asking the user to re-run
Creator with different arguments.

Change-Id: If8196ba3a496406f5539a91e678d26a9a4801b85
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/extensionsystem/pluginmanager.cpp

@@ -354,6 +354,15 @@ bool PluginManager::hasError()
     });
 }
 
+const QStringList PluginManager::allErrors()
+{
+    return Utils::transform<QStringList>(Utils::filtered(plugins(), [](const PluginSpec *spec) {
+        return spec->hasError() && spec->isEffectivelyEnabled();
+    }), [](const PluginSpec *spec) {
+        return spec->name().append(": ").append(spec->errorString());
+    });
+}
+
 /*!
     Returns all plugins that require \a spec to be loaded. Recurses into dependencies.
  */
@@ -1120,8 +1129,9 @@ static TestPlan generateCustomTestPlan(IPlugin *plugin,
 void PluginManagerPrivate::startTests()
 {
     if (PluginManager::hasError()) {
-        qWarning("Errors occurred while loading plugins, skipping test run. "
-                 "For details, start without \"-test\" option.");
+        qWarning("Errors occurred while loading plugins, skipping test run.");
+        for (const QString &pluginError : PluginManager::allErrors())
+            qWarning("%s", qPrintable(pluginError));
         QTimer::singleShot(1, QCoreApplication::instance(), &QCoreApplication::quit);
         return;
     }

src/libs/extensionsystem/pluginmanager.h

@@ -93,6 +93,7 @@ public:
     static const QVector<PluginSpec *> plugins();
     static QHash<QString, QVector<PluginSpec *>> pluginCollections();
     static bool hasError();
+    static const QStringList allErrors();
     static QSet<PluginSpec *> pluginsRequiringPlugin(PluginSpec *spec);
     static QSet<PluginSpec *> pluginsRequiredByPlugin(PluginSpec *spec);