is it reasonable to use ElectricCloud annotation file to reverse-engineer a build system?
Suppose you have a complex build system that you want to rewrite from scratch nicely, but it would take you too long to understand it.
It seems one can use the power of ElectricCloud here a follows.
- Take the annotation with file,lookup.
- Note all the commands that write (change, rename, append, remove) anything.
- For each command line that is multiline or has such things as ';' or 'for' loops, you chop it up into smaller commands, one line preferably.
- For each command, you write a rule like:
one_file_written: files_read Makefile ; command - (If multiple files are written then add
all_other_files_written: one_file_written ; - Now you have a Makefile that should work. But it is big of course! In my case, 300K commands.
- Simplify your Makefile:
- Split command lines into groups by the command.
- For each command, with scripts, categorize arguments used, grouping by arguments and by subdirectories of arguments.
- Use knowledge of semantics of the command to figure out the best way to specify hidden dependencies, or let ElectricCloud do the work if you don't want GNU compatibility.
- Use that to write pattern rules or generate explicit rules, and split into subdirectories makefile fragments, included in the top Makefile by a non-recursive scheme.
- Adorn your new beautiful build system with phony targets that users like, to taste and serve!
Questions:
- Has this been successfully tried before?
- If no, is this crazy and impossible?
Best Answer
Not impossible, but not easy to do correctly either. I don't know that it has been tried, but certainly customers have asked about it. One of them told me that if I can analyze the build in insight off the Annotation file, why not show me a button that I can click to produce an optimized makefile to recreate the same build? I'm sure some of my colleagues will chime in with their opinions about this. Reverse engineering a makefile from an annotation file would be a very cool thing to do if you can pull it off. :)
Thank you! The reason why you did not do it (yet?) as the customer asked, is because, it would be extremely hard, if not impossible, to do in general. I don't intend to do that general step. Instead, I intend to use scripts only to produce rough results. Then I expect to spend months carefully tweaking and adjusting and massaging the system by hand, in order to get it to work. That, not a general step , is I hope within my technical reach. Having said that, if the above "general" goal is impossible, certainly Eric and Company can do it! You guys are the specialists at doing the impossible.
