quoin / tree-diffing

Scala implementation of the Chawathe/Fluri tree matching/edit script algorithm

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Tree Diffing

This is a Scala library that provides a method that accepts two generic ASTs (nodes consist of a label and value) and returns an "edit script" that lists the steps to transform one tree to another in terms of the four operations: insert, delete, move, and update a node.

The algorithm implemented here is also implemented in a Java library by the authors of the Change Distilling paper (see References) with additional functionality (e.g. source code change classification) and an Eclipse plugin. Unfortunately, their library is not available on the Maven Central Repository.

The algorithm is implemented using only immutable data structures.


Perhaps the simplest way to use this is to create an implicit converter from your domain-specific ASTs to the generic AST used by this library:

implicit def toGenericNodeTree(other: MyASTNode) =
  Node(other.someId, other.someLabel, other.someValue, other.children)

Ids must be unique and should be Ints.

If you have the implicit conversion in scope, you can just do:

import com.quoininc.treediffing.EditScript
val editOps: Seq[EditOperations] = EditScript.generate(originalTree, newTree)

editOps will be be a list of simple operations that transforms originalTree into newTree. See the Node object and the Chawathe paper for more details.


The tree matching algorithm comes from this paper:

B. Fluri, M. Würsch, M. Pinzger, H.C. Gall, "Change Distilling: Tree Differencing for Fine- Grained Source Code Change Extraction", IEEE Transactions on Software Engineering, vol. 33, no. 11, pp. 725-743, Nov. 2007

And this paper contains the edit script generator from the matched trees:

S.S. Chawathe, A. Rajaraman, H. Garcia-Molina, and J. Widom, “Change Detection in Hierarchically Structured Information,” Proc. ACM Sigmod Int’l Conf. Management of Data, pp. 493-504, June 1996.