Dep: Create a list of build tags with known special meanings

[sdboyer]

While the course for #291 isn't yet decided, it seems quite likely that we're going to need a list of the build tags (_not_ OS/Arch) that have a generally well-understood public definition. I think the canonical example of this would either be appengine or ignore; however, it's also worth raising something like a debug tag, that (AFAIK) doesn't have widespread adoption, but which might be useful to give a definition to.

Please provide a build tag and a brief description of its use, similar to the following:

• appengine - the source file should be included when compiling a binary to be run on Google's App Engine.
• ignore - designates that the file should be ignored by the compiler unless explicitly instructed otherwise. Its use is purely conventional, acting more as a signal to humans, as any build tag would have the same effect.

[sdboyer]

I'll aim to keep the list in the OP up-to-date with suggestions other folks make in comments.

[zellyn]

One of the googlers with access to the full github bigquery corpus should be able to give you all build tags used anywhere, plus counts. @spf13?

[sdboyer]

@zellyn that seems like a great place to start 😄

[mem]

I had some free quota left, ran some queries against the github corpus, extracted all the lines looking like "// +build", split the line at blanks, grouped and counted. This is the result:

https://docs.google.com/spreadsheets/d/1aImkrXmG1asZ7IgaJxe6HpaEPI8vjUU6Xd1KX-JomFU/edit?usp=sharing

[sdboyer]

@mem that's awesome, thank you!

OK so, filtering out the os, arch, and go version tags, here's a sampling of a few that show up high on the list:

• integration
• no-etcd
• OMIT
• appengine
• acceptance
• experimental
• host
• src
• unit
• cgo
• kvm
• all
• race
• debug
• gofuzz

I'm not sure exactly what I want to do with these yet, but I'm putting them in as a comment here just to record the bit of musing I've done already.

(Obligatory note - this is frequency of appearance of these tags, but information about how frequently these packages are imported is not incorporated. That is, naturally, a relevant metric for our purposes.)