Introduce GRASS_USE_REXTERNAL setting

GRASS GIS, in addition to importing data in its native formats via
`r.in.gdal`/`v.in.ogr` (and likewise `r.import`/v.import`),
also supports `r.external`/`v.external` which only link the data into
the GRASS DB.

Nevertheless, both `r.external` and `v.external` occasionally have problems,
especially on windows. E.g.:

- https://trac.osgeo.org/grass/ticket/3927

GRASS 7 Processing Plugin already has a setting that controls whether
`v.external` is used (disabled by default).

With this commit the complementary setting for `r.external` gets added too.
Usage of `r.external` is disabled by default. This is changing the existing
behavior, which was to use r`r.external`. The downsides of this change
should be the somewhat lower import speed + higher disk usage. Nevertheless
this way we have the same default value as `v.external` + we circumvent the
`r.import/v.import` shortcomings.

Author: pmav99

python/plugins/processing/algs/grass7/Grass7Algorithm.py

@@ -700,29 +700,31 @@ def processOutputs(self, parameters, context, feedback):
             elif isinstance(out, QgsProcessingParameterFolderDestination):
                 self.exportRasterLayersIntoDirectory(outName, parameters, context)
 
-    def loadRasterLayerFromParameter(self, name, parameters, context, external=True, band=1):
+    def loadRasterLayerFromParameter(self, name, parameters, context, external=None, band=1):
         """
         Creates a dedicated command to load a raster into
         the temporary GRASS DB.
         :param name: name of the parameter.
         :param parameters: algorithm parameters dict.
         :param context: algorithm context.
-        :param external: True if using r.external.
+        :param external: use r.external if True, r.in.gdal otherwise.
         :param band: imports only specified band. None for all bands.
         """
         layer = self.parameterAsRasterLayer(parameters, name, context)
         self.loadRasterLayer(name, layer, external, band)
 
-    def loadRasterLayer(self, name, layer, external=True, band=1, destName=None):
+    def loadRasterLayer(self, name, layer, external=None, band=1, destName=None):
         """
         Creates a dedicated command to load a raster into
         the temporary GRASS DB.
         :param name: name of the parameter.
         :param layer: QgsMapLayer for the raster layer.
-        :param external: True if using r.external.
+        :param external: use r.external if True, r.in.gdal if False.
         :param band: imports only specified band. None for all bands.
         :param destName: force the destination name of the raster.
         """
+        if external is None:
+            external = ProcessingConfig.getSetting(Grass7Utils.GRASS_USE_REXTERNAL)
         self.inputLayers.append(layer)
         self.setSessionProjectionFromLayer(layer)
         if not destName:

python/plugins/processing/algs/grass7/Grass7AlgorithmProvider.py

@@ -70,9 +70,16 @@ def load(self):
             Grass7Utils.GRASS_HELP_PATH,
             self.tr('Location of GRASS docs'),
             Grass7Utils.grassHelpPath()))
-        # Add a setting for using v.external instead of v.in.ogr
-        # But set it to False by default because some algorithms
-        # can't be used with external data (need a solid v.in.ogr).
+        # Add settings for using r.external/v.external instead of r.in.gdal/v.in.ogr
+        # but set them to False by default because the {r,v}.external implementations
+        # have some bugs on windows + there are algorithms that can't be used with
+        # external data (need a solid r.in.gdal/v.in.ogr).
+        # For more info have a look at e.g. https://trac.osgeo.org/grass/ticket/3927
+        ProcessingConfig.addSetting(Setting(
+            self.name(),
+            Grass7Utils.GRASS_USE_REXTERNAL,
+            self.tr('For raster layers, use r.external (faster) instead of r.in.gdal'),
+            False))
         ProcessingConfig.addSetting(Setting(
             self.name(),
             Grass7Utils.GRASS_USE_VEXTERNAL,
@@ -90,6 +97,7 @@ def unload(self):
         ProcessingConfig.removeSetting(Grass7Utils.GRASS_LOG_COMMANDS)
         ProcessingConfig.removeSetting(Grass7Utils.GRASS_LOG_CONSOLE)
         ProcessingConfig.removeSetting(Grass7Utils.GRASS_HELP_PATH)
+        ProcessingConfig.removeSetting(Grass7Utils.GRASS_USE_REXTERNAL)
         ProcessingConfig.removeSetting(Grass7Utils.GRASS_USE_VEXTERNAL)
 
     def isActive(self):

python/plugins/processing/algs/grass7/Grass7Utils.py

@@ -50,6 +50,7 @@ class Grass7Utils:
     GRASS_LOG_COMMANDS = 'GRASS7_LOG_COMMANDS'
     GRASS_LOG_CONSOLE = 'GRASS7_LOG_CONSOLE'
     GRASS_HELP_PATH = 'GRASS_HELP_PATH'
+    GRASS_USE_REXTERNAL = 'GRASS_USE_REXTERNAL'
     GRASS_USE_VEXTERNAL = 'GRASS_USE_VEXTERNAL'
 
     # TODO Review all default options formats
@@ -401,6 +402,9 @@ def executeGrass(commands, feedback, outputCommands=None):
                     elif 'Segmentation fault' in line:
                         feedback.reportError(line.strip())
                         feedback.reportError('\n' + Grass7Utils.tr('GRASS command crashed :( Try a different set of input parameters and consult the GRASS algorithm manual for more information.') + '\n')
+                        if ProcessingConfig.getSetting(Grass7Utils.GRASS_USE_REXTERNAL):
+                            feedback.reportError(Grass7Utils.tr(
+                                'Suggest disabling the experimental "use r.external" option from the Processing GRASS Provider options.') + '\n')
                         if ProcessingConfig.getSetting(Grass7Utils.GRASS_USE_VEXTERNAL):
                             feedback.reportError(Grass7Utils.tr(
                                 'Suggest disabling the experimental "use v.external" option from the Processing GRASS Provider options.') + '\n')