Makefile: Respect GOBIN

And use 'go env GOBIN' to detect the user's existing preference.  From
[1]:

> The bin directory holds compiled commands.  Each command is named
> for its source directory, but only the final element, not the entire
> path.  That is, the command with source in DIR/src/foo/quux is
> installed into DIR/bin/quux, not DIR/bin/foo/quux.  The "foo/"
> prefix is stripped so that you can add DIR/bin to your PATH to get
> at the installed commands.  If the GOBIN environment variable is
> set, commands are installed to the directory it names instead of
> DIR/bin.  GOBIN must be an absolute path.
> ...
> Go searches each directory listed in GOPATH to find source code, but
> new packages are always downloaded into the first directory in the
> list.

So if GOBIN is set, it will be non-empty, and we can use $(GOBIN)/...

If GOBIN is unset, 'go env GOBIN' will return an empty string (as it
does on Travis [2]).  In that case, I'm assuming that the package in
question is in the first directory in GOPATH and using the new
FIRST_GOPATH (firstword and subst are documented in [3]).  That's
probably fairly safe, since our previous GOPATH handling assumed it
only contained a single path, and nobody was complaining about that.

Using ?= allows us to skip the 'dirname' call if we end up not needing
GOPKGBASEDIR [4] (e.g. for the 'help' target).  The recursive
expansion could cause an issue if the result of the shell expansions
included a '$', but those seem unlikely in GOPKGBASEDIR, GOMD2MAN, or
the manpage paths.  I haven't used ?= for GOBIN, because we'll always
need the expanded value for the if check.

Using GOMD2MAN allows us to collapse old ||-based recipe into a less
confusing invocation.  And using a static pattern rule [5] for
$(MANPAGES) lets us write a single rule to handle both section 1 and
section 5.

While I was updating the GOPATH handling, I moved .gopathok from the
possibly-shared $(GOPATH)/.gopathok to the
definitely-specific-to-this-project .gopathok.  That may cause some
issues if you rebuild after changing your GOPATH without calling
'clean', but I don't expect folks to change their GOPATH frequently.
And the old approach would fail if different consumers were also using
the same flag path to mean something else (as CRI-O does [6]).

As part of cleaning up .gopathok, I've also collapsed clean's rm calls
into a single invocation.  That will give us the same results with
less process setup/teardown penalties.

[1]: https://golang.org/cmd/go/#hdr-GOPATH_environment_variable
[2]: https://travis-ci.org/projectatomic/libpod/jobs/379345071#L459
[3]: https://www.gnu.org/software/make/manual/html_node/Text-Functions.html
[4]: https://www.gnu.org/software/make/manual/html_node/Setting.html
[5]: https://www.gnu.org/software/make/manual/html_node/Static-Usage.html
[6]: https://github.com/kubernetes-incubator/cri-o/blob/v1.10.1/Makefile#L62

Signed-off-by: W. Trevor King <wking@tremily.us>

Closes: #774
Approved by: mheon

0 files changed, 0 insertions, 0 deletions