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

© 2018 Aunt Bertha