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https://github.com/propensive/umbrageous

Scala compiler plugin to shade packages at compiletime
https://github.com/propensive/umbrageous

compiler-plugin package-shading scala shading

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Scala compiler plugin to shade packages at compiletime

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README 

        
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# Umbrageous



____



Shading a package, effectively renaming it, is one way to avoid conflicts

between packages with the same name. This is a scenario which frequently arises

in complex builts which include transitive dependencies on different versions

of the same library (often called the "diamond dependency problem").



Normally shading is performed on a binary after compilation, but this is slow

and can introduce new problems.  Umbrageous is a compiler plugin which makes it

trivial to compile a library into a package with a distinct prefix without

modifying its source code.



## Features



- rewrites package names at compiletime

- adds no time to the build process

- avoids the need to modify source code

- avoids slow bytecode rewriting after compilation

- customizable with compiler parameters; no configuration files required

- automatically unshades shaded packages in downstream compilations



## Availability Plan



Umbrageous has not yet been published. The medium-term plan is to build Umbrageous

with [Fury](https://github.com/propensive/fury) and to publish it as a source build on

[Vent](https://github.com/propensive/vent). This will enable ordinary users to write and build

software which depends on Umbrageous.



Subsequently, Umbrageous will also be made available as a binary in the Maven

Central repository. This will enable users of other build tools to use it.



For the overeager, curious and impatient, see [building](#building).



## Getting Started



To use Umbrageous, `scalac` must be invoked with two additional parameters:

```sh

scalac -d bin -Xplugin:umbrageous.jar -P:umbrageous:com.example:shaded *.scala`

```



Firstly, `-Xplugin:umbrageous.jar` points the compiler to a JAR file containing

the packaged plugin.



Secondly, `-P:umbrageous:com.example:shaded` tells the plugin to shade

everything inside the `com.example` package behind the prefix `shaded`, i.e.

rewriting `com.example` to `shaded.com.example`.



This `-P` parameter can be provided multiple times to shade different packages.

If more than one parameter matches a package name (e.g.

`-P:umbrageous:com:shade1` and `-P:umbrageous:com.example:shade2`) then the

prefix corresponding to the longest match will be applied to that package.



A downstream project can include an additional wildcard import at the start to

include everything from its shaded dependencies, for example,

```scala

package myproject

import shade.*  // additional import

import com.example

```

will allow the shaded `com.example` package (shaded by the `shade` prefix)

resolve anywhere in the scope of the import (whether imported, or referred to

by fully-qualified classname).



Including the parameter, `-P:umbrageous:com.example:shade` will automatically

unshade the `com.example` package from subsequent compilations without the need

for the import.



Note that this parameter is the same whether applying or using shading.

However, caution should be taken to avoid including nonexistant shaded

packages: doing so will add the synthetic wildcard import, but it will not

resolve, and a compile error will result.



### Limitations



Umbrageous does not currently match package names that are defined in multiple

`package` declarations, such as `com.example` in:



```scala

package com

package example



object Main // ...

```



Additionally, code which references an absolute name, such as

`_root_.com.example.Main` will not find the entity with its new, shaded name.



## Status



Umbrageous is classified as __fledgling__. For reference, Scala One projects are

categorized into one of the following five stability levels:



- _embryonic_: for experimental or demonstrative purposes only, without any guarantees of longevity

- _fledgling_: of proven utility, seeking contributions, but liable to significant redesigns

- _maturescent_: major design decisions broady settled, seeking probatory adoption and refinement

- _dependable_: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version `1.0.0` or later

- _adamantine_: proven, reliable and production-ready, with no further breaking changes ever anticipated



Projects at any stability level, even _embryonic_ projects, can still be used,

as long as caution is taken to avoid a mismatch between the project's stability

level and the required stability and maintainability of your own project.



Umbrageous is designed to be _small_. Its entire source code currently consists

of 48 lines of code.



## Building



Umbrageous will ultimately be built by Fury, when it is published. In the

meantime, two possibilities are offered, however they are acknowledged to be

fragile, inadequately tested, and unsuitable for anything more than

experimentation. They are provided only for the necessity of providing _some_

answer to the question, "how can I try Umbrageous?".



1. *Copy the sources into your own project*

   

   Read the `fury` file in the repository root to understand Umbrageous's build

   structure, dependencies and source location; the file format should be short

   and quite intuitive. Copy the sources into a source directory in your own

   project, then repeat (recursively) for each of the dependencies.



   The sources are compiled against the latest nightly release of Scala 3.

   There should be no problem to compile the project together with all of its

   dependencies in a single compilation.



2. *Build with [Wrath](https://github.com/propensive/wrath/)*



   Wrath is a bootstrapping script for building Umbrageous and other projects in

   the absence of a fully-featured build tool. It is designed to read the `fury`

   file in the project directory, and produce a collection of JAR files which can

   be added to a classpath, by compiling the project and all of its dependencies,

   including the Scala compiler itself.

   

   Download the latest version of

   [`wrath`](https://github.com/propensive/wrath/releases/latest), make it

   executable, and add it to your path, for example by copying it to

   `/usr/local/bin/`.



   Clone this repository inside an empty directory, so that the build can

   safely make clones of repositories it depends on as _peers_ of `umbrageous`.

   Run `wrath -F` in the repository root. This will download and compile the

   latest version of Scala, as well as all of Umbrageous's dependencies.



   If the build was successful, the compiled JAR files can be found in the

   `.wrath/dist` directory.



## Contributing



Contributors to Umbrageous are welcome and encouraged. New contributors may like

to look for issues marked

[beginner](https://github.com/propensive/umbrageous/labels/beginner).



We suggest that all contributors read the [Contributing

Guide](/contributing.md) to make the process of contributing to Umbrageous

easier.



Please __do not__ contact project maintainers privately with questions unless

there is a good reason to keep them private. While it can be tempting to

repsond to such questions, private answers cannot be shared with a wider

audience, and it can result in duplication of effort.



## Author



Umbrageous was designed and developed by Jon Pretty, and commercial support and

training on all aspects of Scala 3 is available from [Propensive

OÜ](https://propensive.com/).



## Name



Plants which are umbrageous provide shade from light, and _Umbrageous_ shades Scala packages.



In general, Scala One project names are always chosen with some rationale,

however it is usually frivolous. Each name is chosen for more for its

_uniqueness_ and _intrigue_ than its concision or catchiness, and there is no

bias towards names with positive or "nice" meanings—since many of the libraries

perform some quite unpleasant tasks.



Names should be English words, though many are obscure or archaic, and it

should be noted how willingly English adopts foreign words. Names are generally

of Greek or Latin origin, and have often arrived in English via a romance

language.



## Logo



The logo shows the shadowy side of a mountain range.



## License



Umbrageous is copyright © 2024 Jon Pretty & Propensive OÜ, and

is made available under the [Apache 2.0 License](/license.md).