# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1530799293 -7200
# Node ID 2b30e05ae0d5ecc02632d3478faad61f1ad66cd5
# Parent  20667fb4b8cfc23e228fada75d4ca7e34684e3e7
Introduced the detection of a particular error before its effects cause a less
helpful error later in the deduction process (involving the absence of accessor
types).

diff -r 20667fb4b8cf -r 2b30e05ae0d5 deducer.py
--- a/deducer.py	Thu Jul 05 16:00:24 2018 +0200
+++ b/deducer.py	Thu Jul 05 16:01:33 2018 +0200
@@ -2136,6 +2136,17 @@
         if constrained:
             self.accessor_constrained.add(location)
 
+        # Complain about situations where no types are valid but where a
+        # specific, known accessor type has been indicated. This absence of
+        # suitable types is likely to occur when the presence of invocations
+        # filters out the accessor type.
+
+        if not class_only_types and not instance_types and not module_types and \
+           invocations and constrained_specific:
+
+            raise DeduceError("In %s, methods of class %s cannot be called directly." %
+                (path, name))
+
     def update_provider_types(self, location, class_types, instance_types, module_types):
 
         """
diff -r 20667fb4b8cf -r 2b30e05ae0d5 tests/contexts.py
--- a/tests/contexts.py	Thu Jul 05 16:00:24 2018 +0200
+++ b/tests/contexts.py	Thu Jul 05 16:01:33 2018 +0200
@@ -5,6 +5,8 @@
         self.x = x
         self.y = 3
         self.z = "zebra libre"
+    def __len__(self):
+        return len(self.z)
 
 c = C([1])
 x = c.x
@@ -45,3 +47,11 @@
 print b             # zebra libre
 print i             # __builtins__.str.basestring.__len__
 print i()           # 11
+
+j = C.__len__
+k = get_using(j, c)
+try:
+    print j()
+except UnboundMethodInvocation:
+    print "j(): invocation of method with class context"
+print k()           # 11
diff -r 20667fb4b8cf -r 2b30e05ae0d5 tests/methods_unbound_bad.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/methods_unbound_bad.py	Thu Jul 05 16:01:33 2018 +0200
@@ -0,0 +1,12 @@
+class C:
+    def __init__(self, x, y, z):
+        self.x = x
+        self.y = y
+        self.z = z
+
+    def c(self):
+        return self.x
+
+c = C(1, 2, 3)
+print c.c() # 1
+print C.c() # bad