Fixed points

[spall]

Summary of meeting June 09 2020

Ideas of how to more easily support build systems that build to a fixed point in Rattle. Examples of systems include Chez Scheme and Latex, where the same file may be written to multiple times until a fixed point is reached.

Allowing a Rattle build to have "phases" was discussed, where the same files can be written to across phases and the version from the last phase to run are saved to the cache.

This could be implemented using "withCmdOptions".

[ndmitchell]

Thanks for the summary. An important point is that running a command from phase 1 might fetch the result from phase 4 quite legitimately - each "phase" would be somehow "better" than the previous one, and the build system would be free to skip forward.