ASTdiff

Compare two commits in a git repository to guarantee that there are no semantic changes.

Use this tool to corroborate that formatting tools don't change the code. If astdiff returns 0, the Abstract Syntax Tree of the files changed in the commits is the same.

Installation

Using pip:

pip install astdiff

Development Installation

To audit the code, or to modify it, install astdiff in development mode. The tool uses poetry to manage dependencies and to build pip installable packages.

$ git clone https://github.com/auntbertha/astdiff.git
$ cd astdiff
$ poetry develop
$ poetry run pytest

To build new packages:

$ poetry build

and distribute the wheel or tarball from the directory dist/.

Usage

The most basic use of astdiff is to check that a reformatting tool didn't change the meaning of the code. When it's called with no arguments astdiff compares the working tree against the HEAD of the current branch:

$ astdiff
Running: git diff --name-only 9d3219ba027d5a56040d23eb9ee3d23f7a410ad5
Checking astdiff/astdiff.py ... ok
✨ All files are equivalent! ✨
$ echo $?
0

astdiff returns 0 if the ASTs are the same, and returns 1 otherwise. The messages are printed to standard error.

astdiff can also check a given commit, a given commit and the working tree, or any pair of commits. It accepts the names of the commits in the same way that git does.

Use -h or --help to get help:

$ astdiff -h
Usage: astdiff.py [OPTIONS] [COMMITS]...

  Compare the AST of all changed files between commits.

  With no arguments, compare between HEAD and the working tree.
  With one argument COMMIT, compare between COMMIT~1 and COMMIT.
  With two arguments, COMMIT1 and COMMIT2, compare between those two.

  (COMMIT2 can be a dot '.' to compare between COMMIT1 and the working tree)

Options:
  -h, --help  Show this message and exit.

Algorithm

The comparison of the ASTs is a very simple recursive function that traverses the trees in a pre-order depth-first search. It can be audited to verify its correctness: astdiff.compare_ast.

LICENSE

The MIT License (MIT)

Copyright © 2018 Aunt Bertha

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.