tools: Injecting standard streams

[tombentley]

The tools framework currently doesn't do anything special for the standard streams (stdout, stderr & stdin): If a tool wants to print to standard output or error it just uses System.out.println()/System.err.println(). I'm wondering if we should change this. If the top level tool was responsible for injecting the PrintStreams (and InputStream in the case of standard input) it would:

• simplify testing (in particular test isolation when testing concurrently, which prevents the TopLevelToolTest running in the compiler tests),
• work better in those cases where the tool is being embedded in another program (rather than the more usual case of command line execution).

It would mean that tools would need to use the injected streams instead of reaching immediately for System.*.

The other way of looking at this is that tools "shouldn't" be reaching for raw streams at all, but should be using logging. In which case this becomes a question about whether it is the top level tool's job to configure logging, or the individual tools', or some combination.

[quintesse]

To me personally logging should not be used for "proper output", ie useful output that is part of the software's operation. I say this because it's normally possible to affect logging output from outside of the program and I don't think we want that.

So I would just go with your first option. (if my opinion means anything hehe)