x/build/cmd/coordinator: report pkg/bin changes, binary size changes

[josharian]

It would be helpful when reviewing changes, particularly toolchain changes, to be able to easily see which pkg/bin files have changed since the parent commit--an easy reviewer's toolstash -cmp.

It'd also be nice to have an automated report about the pkg/bin file size changes.

Could we cheaply/easily add this information to the trybot final report?

cc @bradfitz

[quentinmit]

I'd like to cover this as part of per-commit benchmarks; we can have a fake benchmark that just reports the binary size.

Which binaries should we look at? Every executable file in the built go tree?

[josharian]

I'd like to get these pre-commit, as part of the trybot result report message, as an aid in reviewing.

I had in mind something like this:

• Artifacts are everything in the pkg dir and its subdirs: .a files and compiled tool executables.
• For each artifact, strip its buildid.
• Build a list of all artifacts that differ between commits.
• Remove all items in that list who have a dependency on another item in the list. (If package strings has changed, lots of things will change. This will help reduce the impact of that.)
• Report that list, or at least the first 10 items in it.
• For the binary sizes, report size changes in cmd/go, cmd/compile, and cmd/fix. (The lattermost because its source code rarely changes and it is fairly small.)
• Also report the size change of any file in the pkg dir whose size has changed more than 1%, sorted by amount of change, up to a max of 10.

I'm sure this would need tweaking over time. And some subset of the above would be helpful.