Python-based Java code migration helper (Pyjami)

Python library which helps to automate the migration of Java classes/enums/interfaces.

Scenario

When would you want to use this?

You have a Java project. You want to migrate 99+ classes/enums/interfaces in it. Let's say it contains a com.foo.bar.MyClass, and you want to replace all its usages with those of org.example.newPackage.MyClass.

Your first instinct is a find-and-replace, but you'd have to deal with wildcard imports and partially-qualified references at each level of the package.

You thought of IntelliJ IDEA. It offers a Refactor > Migrate Packages and Classes feature, but:

You have a more complicated mapping to specify. Perhaps you want to migrate lorem.Foo to ipsum.Foo, but for lorem.Bar, you want to migrate it to dolor.Bar. To do so in IntelliJ IDEA, you'd have to manually punch in each mapping rule.
You don't want to migrate all of them in one transaction. Maybe you want to run unit tests after migrating each, committing the changes to a separate revision only if the tests all pass. IntelliJ IDEA doesn't offer such fine-grained control.
Or you simply can't use / would avoid IntelliJ IDEA for some reason.

That's when this toolkit comes to help.

Usage

Migrate one symbol

Please ensure that you've installed these executable programs:

gnu-sed (installed by default on most Linux distros; a manual step on macOS). This is because the BSD edition of sed does not support word boundaries ("\b").
ripgrep, a line-oriented search tool that recursively searches the current directory for a regex pattern.

To migrate usages of com.foo.bar.MyClass to org.example.newPackage.MyClass, use migrate(...) in java_symbol_migration_helpers.py:

from pathlib import Path
from pyjami.java_symbol_migration_helpers import find_suitable_sed_command, migrate
migrate(
    symbol="MyClass",
    path="src/main/com/foo/bar",
    old_package="com.foo.bar",
    new_package="org.example.newPackage",
    repo_dir=Path("repo/"),
    pom_dependency="""
        <dependency>
            <!-- New home for MyClass. -->
            <groupId>org.example</groupId>
            <artifactId>newPackage</artifactId>
        </dependency>
    """,
    sed_executable=find_suitable_sed_command(),
)

Gather information for a list of symbols to migrate

We provide a make_table() function that gathers information about the symbols that are required in the migration process to follow.

Given an iterable (preferably a Pandas Series) of string, each of which being a symbol to migrate, this function returns a Pandas Dataframe with each line indicating the name, the java file path, and the package name of that symbol in the given directory.

For example, if you have MyProject/Lorem.java containing:

package com.example.MyProject;

class Lorem {...}

and you run:

make_table(
    symbols_to_migrate=("Lorem",),
    search_within_directory=pathlib.Path("MyProject/"),
)

you will get a table with one row of these values:

symbol: Lorem
path: MyProject/Lorem.java
package: com.example.MyProject

These are the required information to feed into migrate().

In the case that multiple file paths are found for a given symbol, the first file path that is a child of the firstmost entry in order_of_preference is taken. When none is present, it's treated as if no file path is found for this symbol. Therefore, even if you don't have a preference of which directories to favor, you might still want to provide order_of_preference with at least a search_within_directory, so that at least some choice is taken.

Extra -- Sorting Components in an OpenAPI Contract

This is a common scenario to encounter when migrating handwritten Java code to a library generated from OpenAPI contract. In fact, this is the original case that kicked off this project.

Therefore, Pyjami also provides tools that specifically help with OpenAPI migrations. For example, sort_components_in_contract.py sorts components (data models) in an OpenAPI contract YAML file topologically, so that you can migrate with confidence.

Suppose your OpenAPI contract declares 2 components, Pet and Pets, with Pets referencing ("depending on") Pet:

openapi: "3.0.0"
components:
  schemas:
    Pet:
      type: object
    Pets:
      type: array
      items:
        $ref: "#/components/schemas/Pet"

You can get the optimal order to migrate these symbols using sort_symbols(...):

>>> from pyjami.sort_components_in_contract import sort_symbols
>>> sort_symbols("contract.yaml")
("Pet", "Pets")

This ensures that, by the time you attempt to migrate class Pets, class Pet has already been migrated. This is particularly useful if you want to ensure that the migration of every single symbol should keep the unit tests intact.

Development

This repository uses Poetry for managing dependencies and packaging.

Documentation

Refer to docs/index.html for documentation. It's also published as GitHub pages here.

Pyjami's documentation is generated via the pdoc tool:

pdoc ./pyjami -o ./docs

Pre-Commit Hooks

The hooks are required for the team. Although skipping this step does not prevent you from making a commit, this step is critical in maintaining a uniform coding style across developers.

From now on, whenever you make a new commit, you should see logs like this in your terminal:

Check Yaml...............................................................Passed
Fix End of Files.........................................................Passed
Trim Trailing Whitespace.................................................Passed
black....................................................................Passed

If you see Black failed and modified files:

Check Yaml...............................................................Passed
Fix End of Files.........................................................Passed
Trim Trailing Whitespace.................................................Passed
black....................................................................Failed
- hook id: black
- files were modified by this hook

reformatted path/to/file.py
All done! ✨ 🍰 ✨
1 file reformatted.

Then git add the auto-modified files and retry your git commit command.

Please report a bug if you do not see such messages.

Testing

This project uses pytest for running tests and pytest-cov for collecting test coverage information.

To run the tests, run:

pytest --cov=pyjami

You'll see a report like this:

---------- coverage: platform darwin, python 3.10.6-final-0 ----------
Name                                      Stmts   Miss  Cover
-------------------------------------------------------------
pyjami/__init__.py                            0      0   100%
pyjami/java_symbol_migration_helpers.py     150     18    88%
pyjami/sort_components_in_contract.py        53      8    85%
-------------------------------------------------------------
TOTAL                                       203     26    87%

Then, you can update the coverage badge:

coverage-badge -o coverage.svg

Releasing

This library is available as a package on PyPI here. To release a new version:

Bump the version number in pyproject.toml with a commit. Please follow Semantic Versioning 2.0.0 specifications.
Create a new release on GitHub here.

A GitHub workflow will be automatically triggered to build & publish this package to PyPI. Till eBay have an official account on PyPI, this action will keep on using a PyPI API Token associated with Ming's personal PyPI account. The Token is stored on this GitHub repository as an Action Secret.

License

Apache 2.0.

eBay / pyjami