[Bugfix] Processing @alg decorator support input help string (#40207)

(cherry picked from commit 0b28107)

python/processing/algfactory.py

@@ -194,6 +194,7 @@ def _create_param(self, type, output=False, **kwargs):
         kwargs['description'] = kwargs.pop("label", "")
         kwargs['defaultValue'] = kwargs.pop("default", None)
         advanced = kwargs.pop("advanced", False)
+        help_str = kwargs.pop("help", "")
         try:
             if output:
                 try:
@@ -208,6 +209,8 @@ def _create_param(self, type, output=False, **kwargs):
             parm = make_func(**kwargs)
             if advanced:
                 parm.setFlags(parm.flags() | QgsProcessingParameterDefinition.FlagAdvanced)
+            if not output:
+                parm.setHelp(help_str)
             return parm
         except KeyError as ex:
             raise NotImplementedError("{} not supported".format(str(type)))

tests/src/python/test_processing_alg_decorator.py

@@ -48,6 +48,20 @@ def testalg(instance, parameters, context, feedback, inputs):
         """
 
 
+def define_new_input_help(newid=1):
+    @alg(name=ARGNAME.format(newid), label=alg.tr("Test func"), group="unittest",
+         group_label=alg.tr("Test label"))
+    @alg.help(HELPSTRING.format(newid))
+    @alg.input(type=alg.SOURCE, name="INPUT", label="Input layer", help="The input layer as source")
+    @alg.input(type=alg.DISTANCE, name="DISTANCE", label="Distance", default=30, help="The distance to split the input layer")
+    @alg.input(type=alg.SINK, name="SINK", label="Output layer", help="The output layer as sink")
+    @alg.output(type=str, name="DISTANCE_OUT", label="Distance out")
+    def testalg(instance, parameters, context, feedback, inputs):
+        """
+        Given a distance will split a line layer into segments of the distance
+        """
+
+
 def define_new_doc_string(newid=1):
     @alg(name=ARGNAME.format(newid), label=alg.tr("Test func"), group="unittest",
          group_label=alg.tr("Test label"))
@@ -151,6 +165,22 @@ def test_has_help_from_docstring(self):
         current = alg.instances.pop()
         self.assertEqual("Test doc string text", current.shortHelpString())
 
+    def test_has_input_help(self):
+        define_new_input_help()
+        current = alg.instances.pop()
+        current.initAlgorithm()
+        defs = current.parameterDefinitions()
+        self.assertEqual(3, len(defs))
+        inputs = [
+            ("INPUT", "The input layer as source"),
+            ("DISTANCE", "The distance to split the input layer"),
+            ("SINK", "The output layer as sink"),
+        ]
+        for count, data in enumerate(inputs):
+            parmdef = defs[count]
+            self.assertEqual(data[0], parmdef.name())
+            self.assertEqual(data[1], parmdef.help())
+
 
 class TestAlg(unittest.TestCase):