target: make _get_driver() prioritize drivers named "default"

doc/configuration.rst

@@ -3162,6 +3162,9 @@ To bind the correct driver to the correct resource, explicit ``name`` and
 The property name for the binding (e.g. `port` in the example above) is
 documented for each individual driver in this chapter.
 
+If name is set to "default", this resource/driver will be used when no
+specific constraint is given.
+
 The YAML configuration file also supports templating for some substitutions,
 these are:
 

labgrid/target.py

@@ -159,18 +159,27 @@ def _get_driver(self, cls, *, name=None, activate=True, active=False):
 
         found = []
         other_names = []
+        default = None
         if isinstance(cls, str):
             cls = target_factory.class_from_string(cls)
 
         for drv in self.drivers:
             if not isinstance(drv, cls):
                 continue
+            if drv.name == "default":
+                default = drv
             if name and drv.name != name:
                 other_names.append(drv.name)
                 continue
             if active and drv.state != BindingState.active:
                 continue
             found.append(drv)
+
+        # if no explicit driver name is requested and a "default" driver was saved and
+        # multiple drivers were found, use the default driver
+        if not name and default and len(found) != 1:
+            found = [default]
+
         if not found:
             name_msg = f" named '{name}'" if name else ""
             if other_names:

tests/test_environment.py

@@ -165,6 +165,44 @@ def test_create_multi_drivers(self, tmpdir):
         assert d_a.port is r_a
         assert d_b.port is r_b
 
+    def test_create_multi_drivers_with_default(self, tmpdir):
+        p = tmpdir.join("config.yaml")
+        p.write(
+            """
+        targets:
+          test1:
+            resources:
+            - RawSerialPort:
+                name: "serial_a"
+                port: "/dev/ttyUSB0"
+                speed: 115200
+            - RawSerialPort:
+                name: "default"
+                port: "/dev/ttyUSB0"
+                speed: 115200
+            drivers:
+            - SerialDriver:
+                name: "serial_a"
+                bindings:
+                  port: "serial_a"
+            - SerialDriver:
+                name: "default"
+                bindings:
+                  port: "default"
+        """
+        )
+        e = Environment(str(p))
+        t = e.get_target("test1")
+        r_a = t.get_resource(RawSerialPort, name="serial_a")
+        r_b = t.get_resource(RawSerialPort)
+        assert r_a is not r_b
+        d_a = t.get_driver(ConsoleProtocol, name="serial_a", activate=False)
+        d_b = t.get_driver(ConsoleProtocol, activate=False)
+        assert d_a is not d_b
+
+        assert d_a.port is r_a
+        assert d_b.port is r_b
+
     def test_usbserialport_warning(self, tmpdir):
         p = tmpdir.join("config.yaml")
         p.write(

tests/test_target.py

@@ -50,6 +50,19 @@ class A(Driver):
     assert target.get_driver(A) is a
     assert target.get_driver(A, name="adriver") is a
 
+    # make sure drivers named "default" are prioritized
+    b = A(target, "default")
+    assert target.get_driver(A) is b
+    assert target.get_driver(A, name="adriver") is a
+
+def test_get_driver_multiple_no_default(target):
+    class A(Driver):
+        pass
+
+    a = A(target, "adriver")
+    b = A(target, "default")
+    with pytest.raises(NoDriverFoundError) as excinfo:
+        target.get_driver(A, name="nosuchdriver")
 
 def test_getitem(target):
     class AProtocol(abc.ABC):