1 files changed, 86 insertions, 0 deletions
diff --git a/astroid/astpeephole.py b/astroid/astpeephole.py
new file mode 100644
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+++ b/astroid/astpeephole.py
@@ -0,0 +1,86 @@
+# copyright 2003-2015 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
+# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
+#
+# This file is part of astroid.
+#
+# astroid is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Lesser General Public License as published by the
+# Free Software Foundation, either version 2.1 of the License, or (at your
+# option) any later version.
+#
+# astroid is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
+# for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License along
+# with astroid. If not, see <http://www.gnu.org/licenses/>.
+"""Small AST optimizations."""
+
+import _ast
+
+from astroid import nodes
+
+
+__all__ = ('ASTPeepholeOptimizer', )
+
+
+try:
+    _TYPES = (_ast.Str, _ast.Bytes)
+except AttributeError:
+    _TYPES = (_ast.Str, )
+
+
+class ASTPeepholeOptimizer(object):
+    """Class for applying small optimizations to generate new AST."""
+
+    def optimize_binop(self, node):
+        """Optimize BinOps with string Const nodes on the lhs.
+
+        This fixes an infinite recursion crash, where multiple
+        strings are joined using the addition operator. With a
+        sufficient number of such strings, astroid will fail
+        with a maximum recursion limit exceeded. The
+        function will return a Const node with all the strings
+        already joined.
+        Return ``None`` if no AST node can be obtained
+        through optimization.
+        """
+        ast_nodes = []
+        current = node
+        while isinstance(current, _ast.BinOp):
+            # lhs must be a BinOp with the addition operand.
+            if not isinstance(current.left, _ast.BinOp):
+                return
+            if (not isinstance(current.left.op, _ast.Add)
+                    or not isinstance(current.op, _ast.Add)):
+                return
+
+            # rhs must a str / bytes.
+            if not isinstance(current.right, _TYPES):
+                return
+
+            ast_nodes.append(current.right.s)
+            current = current.left
+
+            if (isinstance(current, _ast.BinOp)
+                    and isinstance(current.left, _TYPES)
+                    and isinstance(current.right, _TYPES)):
+                # Stop early if we are at the last BinOp in
+                # the operation
+                ast_nodes.append(current.right.s)
+                ast_nodes.append(current.left.s)
+                break
+
+        if not ast_nodes:
+            return
+
+        # If we have inconsistent types, bail out.
+        known = type(ast_nodes[0])
+        if any(type(element) is not known
+               for element in ast_nodes[1:]):
+            return
+
+        value = known().join(reversed(ast_nodes))
+        newnode = nodes.Const(value)
+        return newnode