# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1395092450 -3600
# Node ID 43ab2c323dcfbde2d12eec7a48e3d2100123179c
# Parent  78f31936f4e19bf4dfcfa2510e690cc1dda9775c
Supported nested invocations; handled unusable values when deducing attributes.
Refuse to produce guards without any usable deductions.

diff -r 78f31936f4e1 -r 43ab2c323dcf micropython/deduce.py
--- a/micropython/deduce.py	Mon Mar 17 22:37:22 2014 +0100
+++ b/micropython/deduce.py	Mon Mar 17 22:40:50 2014 +0100
@@ -125,11 +125,13 @@
             else:
                 exprs = [expr]
 
-            # For each expression value try and get a concrete
-            # attribute.
+            # For each expression value try and get a concrete attribute.
 
-            for expr in exprs:
-                found_attr = expr.all_attributes().get(attrname)
+            for _expr in exprs:
+                if isinstance(_expr, Instance):
+                    continue
+
+                found_attr = _expr.all_attributes().get(attrname)
 
                 # Where an attribute can be obtained, record its
                 # details.
@@ -283,6 +285,10 @@
 
         node._access_attrs = attributes
 
+        # Return the _attr annotation for instantiation detection.
+
+        return node._attr
+
     def _annotateAttr(self, node, target, attrname):
 
         """
@@ -540,7 +546,7 @@
                 value = attr
 
             if value and isinstance(value, Instance) and not isinstance(value, TypedInstance):
-                node._values[node.name] = expr
+                node._values[node.name] = expr or make_instance()
 
         self._visitGuard(node)
 
@@ -554,6 +560,10 @@
         "Make an annotation stating the acceptable types for a name."
 
         # Need to check any concrete value against deductions.
+        # Where no local observations exist, no guard can usefully be asserted.
+
+        if not node._attrtypes and not node._values:
+            return
 
         types = self.get_targets_from_type_names(node._attrtypes.get(name))
         value = node._values.get(name)
@@ -588,17 +598,18 @@
 
         "Identify any concrete types involved with instantiation."
 
-        for n in node.getChildNodes():
+        for n in node.getChildNodes()[1:]: # ignore node.node
             self.dispatch(n)
 
         # Determine whether the target of the invocation refers to a class.
 
-        attr = node.node._attr
+        attr = self.dispatch(node.node)
 
-        if attr and not isinstance(attr, Instance):
-            value = attr.get_value()
-            if value and isinstance(value, Class):
-                return TypedInstance(value)
+        if attr:
+            if not isinstance(attr, (Instance, UnresolvedName)):
+                value = attr.get_value()
+                if value and isinstance(value, Class):
+                    return TypedInstance(value)
 
     def _visitOperator(self, node):