Add build tags to many commands

[arp242]

Fixes #1464

[fatih]

We should keep :GoBuildTags. :GoBuildTags is dynamic, and sometimes it's handy to have it. go_build_tags on the other hand is permanent, for people who always work on files that have it stick in their files.

[arp242]

:GoBuildTags is dynamic, and sometimes it's handy to have it. go_build_tags on the other hand is permanent, for people who always work on files that have it stick in their files.

What do you mean with "dynamic" and "permanent" in this context? All :GoBuildTags does is set go_build_tags, so it behaves the same?

[fatih]

Yeah I know that it sets it, but it's get resets when you restart vim. Hence the word dynamic. Of course it's not the best solution, because you override the prior value which was set via go_build_tags. The better solution would be to not override go_build_tags , but not sure if that is worth the complexity. But the command is really handy, sometimes you see a new file that has a build tag and you want to change it quickly. I think we should have it, but maybe we should change how it behaves. Dunno.

[bhcleek]

FWIW, I agree with @fatih; I use :GoBuildTags frequently. As a general guideline, anytime we expect users to be able to change a config value during a session, I'm in favor of providing a convenience function to set it.

[arp242]

Okay, fair enough. I added :GoBuildTags back. clarified the documentation, and rebased on mater after the config changes. Should be good to merge now.

Also fixes :GoBuildTags "" to clear the tags. Looks like this didn't work anymore (probably regression from Billy's config PR? Didn't investigate too deeply).

[bhcleek]

The conversion from '' and "" to the empty string should happen in go#cmd#BuildTags. I'll submit a separate PR to do that so it's resolved separately...

[arp242]

Alright, I merged your PR and rebased on master.

[bhcleek]

assuming builds pass, lgtm

[jdef]

[EDIT] My project uses tags sparingly, and I'm running golang 1.10. When I updated vim-go to master the :GoCoverage command complained that tags may only be specified once - the current file/package do not specify any tags. When I rolled back vim-go to the commit just prior to his one, :GoCoverage worked again.