[processing] fix GRASS v.buffer algorithm for case when buffer distance

is taken from the field (fix #19377)

(cherry picked from commit bfb60e4)

Author: alexbruy

python/plugins/processing/algs/grass7/description/v.buffer.txt

@@ -1,5 +1,5 @@
 v.buffer
-Creates a buffer around vector features of given type. 
+Creates a buffer around vector features of given type.
 Vector (v.*)
 QgsProcessingParameterFeatureSource|input|Input vector layer|-1|None|False
 QgsProcessingParameterString|cats|Category values|None|False|True
@@ -8,6 +8,7 @@ QgsProcessingParameterEnum|type|Input feature type|point;line;boundary;centroid;
 QgsProcessingParameterNumber|distance|Buffer distance in map units|QgsProcessingParameterNumber.Double|None|True|None|None
 QgsProcessingParameterNumber|minordistance|Buffer distance along minor axis in map units|QgsProcessingParameterNumber.Double|None|True|None|None
 QgsProcessingParameterNumber|angle|Angle of major axis in degrees|QgsProcessingParameterNumber.Double|0.0|True|0.0|360.0
+QgsProcessingParameterString|layer|Layer number or name ('-1' for all layers)|-1|False|False
 QgsProcessingParameterField|column|Name of column to use for buffer distances|None|input|-1|False|True
 QgsProcessingParameterNumber|scale|Scaling factor for attribute column values|QgsProcessingParameterNumber.Double|1.0|True|None|None
 QgsProcessingParameterNumber|tolerance|Maximum distance between theoretical arc and polygon segments as multiple of buffer|QgsProcessingParameterNumber.Double|0.01|True|None|None

python/plugins/processing/tests/testdata/expected/grass7/buffer_points_field.dbf

@@ -0,0 +1 @@
+GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]]

python/plugins/processing/tests/testdata/expected/grass7/buffer_points_field.prj

@@ -331,6 +331,39 @@ tests:
         name: expected/grass7/buffer_polys_layer2.shp
         type: vector
 
+  - algorithm: grass7:v.buffer
+    name: Buffer using value from field
+    params:
+      -c: false
+      -s: false
+      -t: false
+      GRASS_MIN_AREA_PARAMETER: 0.0001
+      GRASS_OUTPUT_TYPE_PARAMETER: 0
+      GRASS_SNAP_TOLERANCE_PARAMETER: -1.0
+      GRASS_VECTOR_DSCO: ''
+      GRASS_VECTOR_LCO: ''
+      angle: 0.0
+      cats: ''
+      column: id2
+      input:
+        name: points.gml|layername=points
+        type: vector
+      layer: points
+      scale: 1.0
+      tolerance: 0.01
+      type:
+      - 0
+      - 1
+      - 4
+      where: ''
+    results:
+      output:
+        name: expected/grass7/buffer_points_field.shp
+        type: vector
+        compare:
+          fields:
+            fid: skip
+
   - algorithm: grass7:v.surf.rst.cvdev
     name: v.surf.rst - cross-validation errors
     params: