building dotty with cbt

[cvogt]

battle testing CBT by bootstrapping Dotty with CBT.

https://github.com/dotty-staging/dotty/blob/topic/restructure-attempt2/project/Build.scala#L213

[felixmulder]

Binaries to be released from project:

• dotty-compiler (currently in ./src)
• dotty-library (./library)
• dotty-sbt-bridge (./bridge)
• dotty-doc (./dottydoc -- currently, (sbt-project-wise) this guy is actually a part of dotty-compiler because of sbt integration and not released at all)

So for the bootstrap (COMP == scalac):

1. Compile dotty-library with COMP
2. Compile dotty-compiler w COMP depending on (1 and scala-library-2.11.5)
3. Compile dotty-library w 2 (with scala-library-2.11.5 as only dep, no compiler on cp!)
4. Compile dotty-compiler w 2 (with 3 and scala-librar-2.11.5 on cp, no compiler on cp!)

Once we snip the cord from scalac and release only bootstrapped versions, then COMP becomes the previous released compiler.

[felixmulder]

One thing to note is that currently the dotty compiler does weird things with the classpath that it takes from bootclasspath, i.e. it will currently automatically put its running classpath on the classpath of what is being compiled. This is bad and needs to go away asap.

[cvogt]

this merged PR now allows providing a custom Dotty compiler, which is necessary for bootstrapping: https://github.com/cvogt/cbt/pull/333

[cvogt]

PR that bootstraps Dotty is open in dotty-staging: https://github.com/lampepfl/dotty/pull/1964