Attribute linkmode in go_binary doesn't support select

[alextercete]

When trying to create a cross-platform go_binary target that works for Linux/Android and 32/64 bits, the standard approach would be to use a select (unless #4478 is fixed):

config_setting(
    name = "armv7_linux",
    constraint_values = [
        "@platforms//cpu:armv7",
        "@platforms//os:linux",
    ],
)

go_binary(
    name = "run",
    srcs = ["run.go"],
    linkmode = select({
        ":armv7_linux": "normal",
        "//conditions:default": "pie",
    }),
    pure = "on",
)

However, this fails with:

ERROR: (...): in go_non_executable_binary rule //:run: Returning RunEnvironmentInfo from a non-executable, non-test target has no effect

It looks like the issue is that you're not handling a select in go_binary_macro:

rules_go/go/private/rules/wrappers.bzl

Lines 42 to 45 in 74199c9

	if kwargs.get("linkmode", LINKMODE_NORMAL) in LINKMODES_EXECUTABLE:
	go_binary(name = name, **kwargs)
	else:
	go_non_executable_binary(name = name, **kwargs)

[dzbarsky]

This is a bit tricky to support, the linkmode determines whether the output should be executable, which is why the macro redirects to different targets. It wouldn't be able to do that with a select, but you could define two targets, one for each linkmode, and an alias that selects between them?

Though it sounds like all of this is moot if the Android linkmode is fixed, want to send a PR?

[alextercete]

you could define two targets, one for each linkmode, and an alias that selects between them?

Yes, this is the workaround I'm using at the moment.

Though it sounds like all of this is moot if the Android linkmode is fixed, want to send a PR?

Sounds good, I'm working on a fix for #4478 and I'll submit it soon. But this one might be worth fixing as well. I see two possible approaches:

1. Identify linkmode is a select and fail with a descriptive error message.
2. Expand the select and check its item values. If they're all executable, run go_binary; if they're all non-executable, run go_non_executable_binary; fail with a descriptive error message otherwise.

Personally, I'd prefer the latter, as it would give more flexibility to users. For example, I could want to always use PIE except when target CPU is 32-bits.

Let me know your thoughts. Happy to provide a PR for either option.

[dzbarsky]

Last I checked Bazel doesn't have programmatic access to the select contents, you have to parse the str() results which is pretty janky. But maybe I'm misremembering! Option 1 sounds reasonable, though we'll essentially get it "for free" when we move to symbolic macros

[alextercete]

Last I checked Bazel doesn't have programmatic access to the select contents, you have to parse the str() results which is pretty janky.

You're right. I thought I had seen this done before, but my search seems to agree with you that it isn't possible.

What if we always called go_binary if linkmode is a select?