srewrite plugin

In order to compile Scala code written for scalac 2 with dotty, some changes are necessary. The goal of this tool is to perform these changes automatically, with minimal differences in the source code.

Here's a list of these changes:

[DONE] explicit unit return types (ie. no "procedure syntax" for defs)
[DONE] explicit unit return types for abstract methods as well
[DONE] explicit types for implicit vals
[DONE] existential types (forSome) rewriting
[DONE] rewrite early initializers to late (normal) initializers and emit a big warning that it has to be reviewed manually
[TODO] add an @volatile annotation to all lazy vals
[Not needed] Autotupling. For instance, why does List(1, 2, 3).toSet() return false? See also this discussion and this blog post.
[TODO] do not add newline to end of file if there's none
[TODO] imports are shadowed by class definitions in dotty (see test/importShadowing.scala for an example)
[TODO] In val defs of the form val x = new SomeClass { refinements... }, scalac infers a refined type as type of x, whereas dotty only infers SomeClass, so the rewrite tool should insert an explicit refined type for x.
[TODO] probably we need more transformations that we're not yet aware of

The challenge: Don't just reprint the whole code using any PrettyPrinter, loosing all formatting and comments. Modify the code as little as possible.

Demo: The diff between original Scala source and source rewritten by srewrite.

Build process

From srewrite directory run:

$ sbt assembly

Produced jar should be in project's target directory.

To add srewrite plugin jar to local ivy repo use:

$ sbt publish-local

Required jar should have similar path:

~/.ivy2/local/org.scala-lang.plugins/srewriteplugin_2.10/0.1.0/jars/srewriteplugin_2.10-assembly.jar

See http://scala-sbt.org/release/docs/Getting-Started/Setup.html for instructions to setup sbt.

Usage

Sbt projects:

In the target project add to build.sbt (or build.scala) following option:

libraryDependencies += compilerPlugin("org.scala-lang.plugins" %% "srewriteplugin" % "0.1.0")

Compile the project:

$ sbt compile

After the compilation generated sources should be in sourceFromAST folder (projectFolder/sourceFromAST).

Command-line:

To compile the project from the command-line use:

$ scalac -Xplugin:/path/to/jar/srewriteplugin_2.10-assembly.jar hello/world/*.scala

Options

dir-name - setup custom name for folder with regenerated sources

scalacOptions += "-P:srewriteplugin:dir-name:printAST"

base-dir - setup custom path for regenerated sources

scalacOptions += "-P:srewriteplugin:base-dir:/path/for/generated/sources"

oversrc - overwrite original sources with generated during the compilation.

scalacOptions += "-P:srewriteplugin:oversrc"

Example

$ scalac -Xplugin:path/to/jar/srewriteplugin_2.10-assembly.jar -P:srewriteplugin:base-dir:/path/to/generated/sources -P:srewriteplugin:dir-name:source-hello-world hello/world/*.scala

Regenerated sources should be in sourceFromAST folder.

A sample sbt configuration can be found in srewrite-test project: https://github.com/samuelgruetter/srewrite-test