Gumtree Spoon AST Diff

Computes the AST difference between two Spoon abstract syntax trees using the Gumtree algorithm.

If you use this, please cite:

Fine-grained and Accurate Source Code Differencing (Jean-Rémy Falleri, Floréal Morandat, Xavier Blanc, Matias Martinez, Martin Monperrus), In Proceedings of the International Conference on Automated Software Engineering, 2014. DOI: 10.1145/2642937.2642982.

@inproceedings{gumtree,
 title = {Fine-grained and Accurate Source Code Differencing},
 author = {Falleri, Jean-R{\'e}my and Morandat, Flor{\'e}al and Blanc, Xavier and Martinez, Matias and Monperrus, Martin},
 url = {https://hal.archives-ouvertes.fr/hal-01054552/file/main.pdf},
 booktitle = {{Proceedings of the International Conference on Automated Software Engineering}},
 pages = {313-324},
 year = {2014},
 doi = {10.1145/2642937.2642982},
}

Differences between plain gumtreediff and gumtree-spoon-ast-diff

What is the main difference between gumtree-spoon-ast-diff and gumtreediff?

• The tree of gumtree-spoon-ast-diff is carefully designed to provide better AST diffs for Java as opposed to vanilla gumtreediff. Simply compare the AST diffs on your own data.
• The nodes involved in the diff can be pretty-printed through the pointer to the original Spoon nodes (see method changedNode, commonAncestor, getSrcNode)
• The nodes involved in the diff can be further analyzed with Spoon's API
• The configuration parameters of AST differencing have beeen fine tuned with hyper-optimization, see Hyperparameter Optimization for AST Differencing (IEEE TSE)

Usage

The main class is used this way:

gumtree.spoon.AstComparator <file_1> <file_2>

As API:

• Diff of two Spoon AST

new AstComparator().compare((CtElement) el1, (CtElement) el2);

• Diff of two Files (It parses each file for creating a Spoon AST, then it compares both ASTs)

new AstComparator().compare((File) f, (File) f2);

• Diff of two Snippets (It parses each Snippet for creating a Spoon AST, then it compares both ASTs)

new AstComparator().compare((String) s1, (String) s2);

Gumtree Spoon AST Diff uses the AST matcher called SimpleGumtree since Sep 2023. Ihe API setMatcher provides the possibility to change it: The mentioned compare methods can be configured accordingly, as in the following example.

		AstComparator comp = new AstComparator();
		
		//We define a DiffConfiguration
		DiffConfiguration diffConfiguration = new DiffConfiguration();
		//Set the matcher to be used
		diffConfiguration.setMatcher(new CompositeMatchers.ClassicGumtree());
		//Set values for hyperparameters
		GumtreeProperties properties = new GumtreeProperties();
		properties.tryConfigure(ConfigurationOptions.bu_minsim, 0.2);
		properties.tryConfigure(ConfigurationOptions.bu_minsize, 600);
		properties.tryConfigure(ConfigurationOptions.st_minprio, 1);
		properties.tryConfigure(ConfigurationOptions.st_priocalc, size);
		diffConfiguration.setGumtreeProperties(properties);
		
		//Now, compute the diff with the configuration diffConfiguration
		Diff resultClassicMatcher = comp.compare(fl, fr, diffConfiguration);

In the previous snippet, we call the diff algorithm with a particular setup: ClassicGumtree matcher and a set of hyperparameters which minimize the size of the edit-scripts. The values of these hyperparameters were found using DAT (Diff Auto-Tuning).

@misc{dat,
  author = {Martinez, Matias and Falleri, Jean-Rémy and Monperrus, Martin},
  
  title = {Hyperparameter Optimization for AST Differencing},
  
  publisher = {arXiv},
  
  year = {2020},
  
  doi = {10.48550/ARXIV.2011.10268},
  
  url = {https://arxiv.org/abs/2011.10268},
   
  keywords = {Software Engineering (cs.SE), FOS: Computer and information sciences, FOS: Computer and information sciences},
}

Testing AST differencing

gumtree-spoon-ast-diff is heavily tested. The testing of AST tree differencing is quite interesting.

There are cases where the oracle is pretty clear, for instance for the deletion of a node.

// there is only one deletion at line 442
assertEquals(operations.size(), 1);
assertTrue(diff.containsOperation(operations, OperationKind.Delete, "Literal", "\"UTF-8\""));
assertEquals(442, result.changedNode().getPosition().getLine());

or for the addition of a single node

assertEquals(operations.size(), 1);
assertTrue(diff.containsOperation(operations, OperationKind.Insert, "Invocation", "append"));

However, with the presence of moves, the answer is less clear. For instance, an insert+delete instead of a move is correct, although not optimal. However, in this case, there are still definitive oracles: for instance, you are sure that the change happened within a certain node

// the change happened in System.out.println() at line 334
CtElement ancestor = result.commonAncestor();
assertTrue(ancestor instanceof CtInvocation);
assertEquals("println", ((CtInvocation)ancestor).getExecutable().getSimpleName());
assertEquals(344,ancestor.getPosition().getLine());

To conclude, for testing AST differencing, there is not always a unique and complete, it is a blend of assertions on:

• the number of changes
• the presence of certain changes
• the location of the change (node type and content)
• the location of the change (line number)

Download

Build your own version (mvn install) or download the latest stable JAR on Maven.

Deploy

To deploy a new version on Maven Central:

• Deploy from Travis directly (easier, all keys configured in .travis.yml):
  • Prepare branch "deploy"
    • git branch -D deploy (delete previous release)
    • git checkout -b deploy
  • Update version number (if it ends with "-SNAPSHOT" it is pushed as Snapshot otherwise as release)
  • Commit to branch "deploy" (only this branch deploys to Maven Central)
    • git commit -m release pom.xml
  • Push to branch "deploy" (you have to force push)
    • git push origin deploy -f
• Deploy from localhost:
  • Update version number
  • mvn -Prelease verify deploy:deploy
  • Commit and push

License

Copyright 2016 Matias Martinez

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.