When processing is initialized in external scripts, ensure the GRASS,

SAGA and OTB providers are included by default

Fixes #45935

python/core/auto_generated/qgsapplication.sip.in

@@ -85,7 +85,7 @@ to change due to centralization.
     static const char *QGIS_ORGANIZATION_DOMAIN;
     static const char *QGIS_APPLICATION_NAME;
 
-    QgsApplication( SIP_PYLIST argv, bool GUIenabled, QString profileFolder = QString(), QString platformName = "desktop" ) / PostHook = __pyQtQAppHook__ / [( int &argc, char **argv, bool GUIenabled, const QString &profileFolder = QString(), const QString &platformName = "desktop" )];
+    QgsApplication( SIP_PYLIST argv, bool GUIenabled, QString profileFolder = QString(), QString platformName = "external" ) / PostHook = __pyQtQAppHook__ / [( int &argc, char **argv, bool GUIenabled, const QString &profileFolder = QString(), const QString &platformName = "desktop" )];
 %Docstring
 Constructor for QgsApplication.
 

python/plugins/processing/core/Processing.py

@@ -114,6 +114,33 @@ class Processing(object):
                 p = c()
                 if QgsApplication.processingRegistry().addProvider(p):
                     Processing.BASIC_PROVIDERS.append(p)
+
+            if QgsApplication.platform() == 'external':
+                # for external applications we must also load the builtin providers stored in separate plugins
+                try:
+                    from grassprovider.Grass7AlgorithmProvider import Grass7AlgorithmProvider
+                    p = Grass7AlgorithmProvider()
+                    if QgsApplication.processingRegistry().addProvider(p):
+                        Processing.BASIC_PROVIDERS.append(p)
+                except ImportError:
+                    pass
+
+                try:
+                    from otbprovider.OtbAlgorithmProvider import OtbAlgorithmProvider
+                    p = OtbAlgorithmProvider()
+                    if QgsApplication.processingRegistry().addProvider(p):
+                        Processing.BASIC_PROVIDERS.append(p)
+                except ImportError:
+                    pass
+
+                try:
+                    from sagaprovider.SagaAlgorithmProvider import SagaAlgorithmProvider
+                    p = SagaAlgorithmProvider()
+                    if QgsApplication.processingRegistry().addProvider(p):
+                        Processing.BASIC_PROVIDERS.append(p)
+                except ImportError:
+                    pass
+
             # And initialize
             ProcessingConfig.initialize()
             ProcessingConfig.readSettings()

python/plugins/processing/tests/ProcessingGeneralTest.py

@@ -107,6 +107,21 @@ class TestProcessingGeneral(unittest.TestCase):
         # Python should NOT have ownership
         self.assertFalse(sip.ispyowned(layer))
 
+    def testProviders(self):
+        """
+        When run from a standalone script (like this test), ensure that the providers from separate plugins are available
+        """
+        providers = [p.id() for p in QgsApplication.processingRegistry().providers()]
+        self.assertIn('qgis', providers)
+        self.assertIn('native', providers)
+        self.assertIn('gdal', providers)
+        self.assertIn('project', providers)
+        self.assertIn('script', providers)
+        self.assertIn('model', providers)
+        self.assertIn('grass7', providers)
+        self.assertIn('saga', providers)
+        self.assertIn('otb', providers)
+
 
 if __name__ == '__main__':
     nose2.main()

src/core/qgsapplication.h

@@ -181,7 +181,7 @@ class CORE_EXPORT QgsApplication : public QApplication
      * \param profileFolder optional string representing the profile to load at startup
      * \param platformName the QGIS platform name, e.g., "desktop", "server", "qgis_process" or "external" (for external CLI scripts)
      */
-    QgsApplication( SIP_PYLIST argv, bool GUIenabled, QString profileFolder = QString(), QString platformName = "desktop" ) / PostHook = __pyQtQAppHook__ / [( int &argc, char **argv, bool GUIenabled, const QString &profileFolder = QString(), const QString &platformName = "desktop" )];
+    QgsApplication( SIP_PYLIST argv, bool GUIenabled, QString profileFolder = QString(), QString platformName = "external" ) / PostHook = __pyQtQAppHook__ / [( int &argc, char **argv, bool GUIenabled, const QString &profileFolder = QString(), const QString &platformName = "desktop" )];
     % MethodCode
     // The Python interface is a list of argument strings that is modified.