# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1389653936 -3600
# Node ID 3f0fd4b7137784afcb9de63695a3c208c5f8a282
# Parent  fd113b9d829c2c5505e4bff9849cf5ee1f874eea
Added support for detecting accesses of potentially unassigned locals.

diff -r fd113b9d829c -r 3f0fd4b71377 micropython/branch.py
--- a/micropython/branch.py	Mon Jan 13 23:58:23 2014 +0100
+++ b/micropython/branch.py	Mon Jan 13 23:58:56 2014 +0100
@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 
 """
-Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Paul Boddie <paul@boddie.org.uk>
+Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014 Paul Boddie <paul@boddie.org.uk>
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -414,6 +414,13 @@
 
         self.scope_usage[-1][name] = scope
 
+    def defined_as_local(self, name):
+
+        "Return the scope defined for 'name' or None if it is not yet defined."
+
+        scope = self.scope_usage[-1].get(name)
+        return scope and (scope == "local" or isinstance(scope, ScopeConflict) and scope.is_benign())
+
     def note_scope(self, name, scope):
 
         """
@@ -426,8 +433,11 @@
         if scope_usage.has_key(name):
             found_scope = scope_usage[name]
             if isinstance(found_scope, ScopeConflict):
-                raise InspectError("Scope conflict for %r: defined as %s." % (
-                    name, ", ".join(found_scope.scopes)))
+                if not found_scope.is_benign():
+                    raise InspectError("Scope conflict for %r: defined as %s." % (
+                        name, ", ".join(found_scope.scopes)))
+                else:
+                    print >>sys.stderr, "Warning: name %r in %s may not be defined in all cases." % (name, self.full_name())
 
         scope_usage[name] = scope
 
@@ -645,6 +655,8 @@
 
                 else:
                     attr, scope, full_name = self._get_with_scope(name, external=1)
+                    if not attr:
+                        scope = "unset"
 
                 # Attempt to record the scope, testing for conflicts.
 
@@ -748,13 +760,21 @@
 class ScopeConflict:
 
     """
-    A scope conflict caused when different code branches contribute different
-    sources of names.
+    A class whose instances provide a collection of scope alternatives, either
+    potentially benign or indicating a serious problem.
+
+    A scope conflict is caused when different code branches contribute different
+    sources of names or where branches neglect to contribute names at all. Where
+    the sources (scopes) indicated are different, a serious problem exists
+    because the name has no single way of being accessed.
     """
 
     def __init__(self, scopes):
         self.scopes = scopes
 
+    def is_benign(self):
+        return len(self.scopes) == 2 and "unset" in self.scopes
+
 class UnsetType:
 
     "A None-like value."
diff -r fd113b9d829c -r 3f0fd4b71377 micropython/data.py
--- a/micropython/data.py	Mon Jan 13 23:58:23 2014 +0100
+++ b/micropython/data.py	Mon Jan 13 23:58:56 2014 +0100
@@ -221,7 +221,7 @@
 
         # Locals.
 
-        if not external and self.has_key(name):
+        if not external and self.defined_as_local(name) and self.has_key(name):
             return self[name], "local", self.full_name()
 
         # Outer scopes.
diff -r fd113b9d829c -r 3f0fd4b71377 tests/local_potentially_unassigned.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/local_potentially_unassigned.py	Mon Jan 13 23:58:56 2014 +0100
@@ -0,0 +1,10 @@
+#!/usr/bin/env python
+
+def f(a):
+    if a:
+        x = 1
+    return x
+
+result_1 = f(1)
+
+# vim: tabstop=4 expandtab shiftwidth=4