# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1339357853 -7200
# Node ID 05abcd0316a58fd01062b33a618b9a196f25a00d
# Parent  3815443bf7de8c20292907081de34c3bbf4ae704
Introduced separate handling of abandoned attribute usage branches so that
exception handlers can restore usage from such branches.

diff -r 3815443bf7de -r 05abcd0316a5 micropython/data.py
--- a/micropython/data.py	Sun Jun 10 18:38:37 2012 +0200
+++ b/micropython/data.py	Sun Jun 10 21:50:53 2012 +0200
@@ -114,6 +114,10 @@
         self.scope_usage = [{}]     # stack of scope usage
         self.scope_shelves = []
 
+        # Abandoned usage, useful for reviving usage for exception handlers.
+
+        self.abandoned_users = [[]]          # stack of lists of users
+
         # Define attribute usage to identify active program sections.
         # Attribute users are AST nodes defining names.
 
@@ -751,6 +755,10 @@
         scope_usage.update(self.scope_usage[-1])
         self.scope_usage.append(scope_usage)
 
+        # Retain a record of abandoned branch users.
+
+        self.abandoned_users.append([])
+
     def _connect_users_to_branch(self, attribute_users, node):
 
         """
@@ -767,16 +775,21 @@
             self._init_attribute_user(user)
             user._attrbranches.append(node)
 
-    def _abandon_branch(self):
+    def _abandon_branch(self, retain_branch=True):
 
         """
         Abandon scope usage, permitting locally different scopes for names,
         provided these cannot "escape" from the branch.
         """
 
-        self.attribute_users[-1] = abandoned_branch_users
+        attribute_users = self.attribute_users[-1]
+
+        self.attribute_users[-1] = {}
         self.scope_usage[-1] = abandoned_branch_scope
 
+        if retain_branch:
+            self.abandoned_users[-1].append(attribute_users)
+
     def _suspend_broken_branch(self):
 
         """
@@ -785,10 +798,9 @@
 
         attribute_users = self.attribute_users[-1]
 
-        if not isinstance(attribute_users, AbandonedBranchUsers):
-            users = self.suspended_broken_users[-1]
-            users.append(attribute_users)
-            self._abandon_branch()
+        users = self.suspended_broken_users[-1]
+        users.append(attribute_users)
+        self._abandon_branch(False)
 
     def _suspend_continuing_branch(self):
 
@@ -798,10 +810,9 @@
 
         attribute_users = self.attribute_users[-1]
 
-        if not isinstance(attribute_users, AbandonedBranchUsers):
-            loop_node, users = self.suspended_continuing_users[-1]
-            users.append(attribute_users)
-            self._abandon_branch()
+        loop_node, users = self.suspended_continuing_users[-1]
+        users.append(attribute_users)
+        self._abandon_branch(False)
 
     def _shelve_branch(self):
 
@@ -833,6 +844,12 @@
         new_users = merge_mapping_dicts(all_shelved_users)
         self.attribute_users[-1] = new_users
 
+        # Abandoned users are retained for exception handling purposes.
+
+        all_abandoned_users = self.abandoned_users.pop()
+        new_abandoned_users = merge_mapping_dicts(all_abandoned_users)
+        self.abandoned_users[-1].append(new_abandoned_users)
+
         # Combine the scope usage.
 
         scope_usage = self.scope_usage[-1]
@@ -919,6 +936,18 @@
         new_users = merge_mapping_dicts(suspended_users + [current_users])
         self.attribute_users[-1] = new_users
 
+    def _resume_abandoned_branches(self):
+
+        """
+        Incorporate users from abandoned branches into the current set of active
+        users. The abandoned branches are taken from the containing branch.
+        """
+
+        current_users = self.attribute_users[-1]
+        abandoned_users = self.abandoned_users[-2]
+        new_users = merge_mapping_dicts(abandoned_users + [current_users])
+        self.attribute_users[-1] = new_users
+
     # Scope usage methods.
 
     def define_scope(self, name, scope):
@@ -979,15 +1008,6 @@
 
     values = items = keys
 
-class AbandonedBranchUsers(EmptyDict):
-
-    """
-    A class providing a value or state for an abandoned branch distinct from an
-    empty usage dictionary.
-    """
-
-    pass
-
 class AbandonedBranchScope(EmptyDict):
 
     """
@@ -997,7 +1017,6 @@
 
     pass
 
-abandoned_branch_users = AbandonedBranchUsers()
 abandoned_branch_scope = AbandonedBranchScope()
 
 class ScopeConflict:
diff -r 3815443bf7de -r 05abcd0316a5 micropython/inspect.py
--- a/micropython/inspect.py	Sun Jun 10 18:38:37 2012 +0200
+++ b/micropython/inspect.py	Sun Jun 10 21:50:53 2012 +0200
@@ -410,6 +410,9 @@
     def resume_continuing_branches(self):
         self.get_namespace()._resume_continuing_branches()
 
+    def resume_abandoned_branches(self):
+        self.get_namespace()._resume_abandoned_branches()
+
     def define_attribute_user(self, node):
 
         """
@@ -1216,15 +1219,16 @@
         return self._visitOperator(node, self.in_assignment and "AssSubscript" or "Subscript")
 
     def visitTryExcept(self, node):
+        self.new_branchpoint()
         self.dispatch(node.body)
 
-        self.new_branchpoint()
-
-        # NOTE: Attempt to recover abandoned branches from the body.
-
         for name, var, n in node.handlers:
             self.new_branch(n)
 
+            # Any abandoned branches from the body can now be resumed.
+
+            self.resume_abandoned_branches()
+
             # Establish the local for the handler.
 
             if var is not None:
@@ -1234,6 +1238,10 @@
 
             self.shelve_branch()
 
+        # The else clause maintains the usage from the body but without the
+        # abandoned branches since they would never lead to the else clause
+        # being executed.
+
         self.new_branch(node.else_ or NullBranch())
         if node.else_ is not None:
             self.dispatch(node.else_)