golang portgroup 1.0: add support for -ldflags

[emcrisostomo (Enrico Maria Crisostomo)]

The go build command may optional specify linker flags using -ldflags that are passed to go tool link. I see two opportunities for improvements here: one, is to specify an additional variable to pass link variables, and the other is possibly adding additional support for -X flags.

The basic issue here (as discussed briefly in ​https://github.com/macports/macports-ports/pull/6442), is that -ldflags have to be specified in build.cmd, where they are basically appended. If specified in build.args, the build fails because they're set after the build.target, while go expects them between the build.cmd and the build.args.

Additionally, in Go it's idiomatic to set build-time variable through the -X link flag, resulting in multiple space-separated, quoted -X flags passed down as a single -ldflags argument, as in the referenced pull request:

build.cmd ${go.bin} build -ldflags \
        "\"-X github.com/docker/cli/cli/version.GitCommit=${docker_gitcommit} -X github.com/docker/cli/cli/version.Version=${version} -X \\\"github.com/docker/cli/cli/version.BuildTime=${build_time}\\\"\""

I suggest adding such support in the portgroup, to enable passing ldflags in a dedicated variable, and optionally offer some facility to simplify the resulting port syntax.

[emcrisostomo (Enrico Maria Crisostomo)]

I just merged an update on another port (devel/dep) whose build script generates a very similar ldflags string and may benefit from the same changes in the golang portgroup.

[kencu (Ken)]

there are also features like this

build.pre_args-prepend

These are a bit awkward perhaps, but may help you shoehorn flags in right where you want them to go, in certain cases.

[mascguy (Christopher Nielsen)]

Add keyword portgroup, to pg-related tickets