pylightning: Exception if we have unfulfilled positional arguments

This caused me to backtrack quite a bit, so this should help debugging
in the future.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

contrib/pylightning/lightning/plugin.py

@@ -252,7 +252,7 @@ class Plugin(object):
 
         arguments = OrderedDict()
         for name, value in sig.parameters.items():
-            arguments[name] = inspect.Signature.empty
+            arguments[name] = inspect._empty
 
         # Fill in any injected parameters
         if 'plugin' in arguments:
@@ -267,7 +267,7 @@ class Plugin(object):
         else:
             pos = 0
             for k, v in arguments.items():
-                if v is not inspect.Signature.empty:
+                if v != inspect._empty:
                     continue
                 if pos < len(params):
                     # Apply positional args if we have them
@@ -280,6 +280,15 @@ class Plugin(object):
                     arguments[k] = sig.parameters[k].default
                 pos += 1
 
+        missing = [k for k, v in arguments.items() if v == inspect._empty]
+        if missing:
+            raise TypeError("Missing positional arguments ({given} given, "
+                            "expected {expected}): {missing}".format(
+                                missing=", ".join(missing),
+                                given=len(arguments) - len(missing),
+                                expected=len(arguments)
+                            ))
+
         ba = sig.bind(**arguments)
         ba.apply_defaults()
         return func(*ba.args, **ba.kwargs)

contrib/pylightning/lightning/test_plugin.py

@@ -1,5 +1,6 @@
 from .plugin import Plugin, Request
 import itertools
+import pytest
 
 
 def test_positional_inject():
@@ -42,9 +43,28 @@ def test_positional_inject():
         """
         assert (a, b, c, d, e) == (1, 2, 3, 4, 42)
 
+    def count(plugin, count, request):
+        assert count == 42 and plugin == p
+
     funcs = [pre_args, in_args, post_args, post_kwargs, in_multi_args]
 
     for func, request in itertools.product(funcs, [rdict, rarr]):
         p._exec_func(func, request)
 
     p._exec_func(extra_def_arg, rarr)
+
+    p._exec_func(count, Request(
+        plugin=p,
+        req_id=1,
+        method='func',
+        params=[42],
+    ))
+
+    # This should fail since it is missing one positional argument
+    with pytest.raises(ValueError):
+        p._exec_func(count, Request(
+            plugin=p,
+            req_id=1,
+            method='func',
+            params=[])
+        )