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Introduction

This is an early experiment about Semantic Diff for the Java language. Our goal is to integrate it into NetBeans once it is finished.

What semantic diff is

It is a diff between multiple files, where the differences are expressed with criteria which are related to the file content's semantic.

Examples of semantic differences:

  • A new function has been introduced into a class.
  • A new function call was added into a block of code.
  • The 2nd parameter of a function call was modified.
  • A class inherits from a different class.
  • A function was moved to a super class.

Examples of differences which are not semantical:

  • A method have been re-indented.
  • A new line was added into a piece of code which was too long.
  • A function was moved to a different location inside the same class.
  • A local variable was renamed.

Why it is cool

Ignoring irrelevant changes

When developers want to review a commit, they use a diff tool. Sometimes, they don't want to list all the details which do not change the behavior of a program, and they only want to see changes that matter. A semantic diff can help them to select which type of changes they think matter, and help them save some time by ignoring the unimportant changes.

Ignoring irrelevant conflicts

Another reason why a semantic diff can be cool is when you have to merge 2 branches together in your code. A classical diff tool might reveal conflicts on lines being modified on each branch, while a semantic diff might be able to see the changes from a different angle and still be able to merge them if their semantic doesn't conflict which each other.

For example:

  • There is a section of code which was modified on both branch A and branch B.
  • On branch A, the change is just a code formatting change.
  • On branch B, the change is a variable which was renamed.
  • The semantic diff doesn't detect semantic conflict and a semantic merge tool can merge the changes without bothering the developer.

License

This project is distributed under the Affero General Public License (AGPL) version 3. The license's terms are defined in the file LICENSE.txt. For information about our license choice: Why Affero GPL.

Original Developers

David Andreoletti & Vincent Cantin

Contributions

Contributions are welcome, do not hesitate to create an issue and/or start a pull request.