Add an alternative way to specify build enviroment variables

[oliverpool]

Currently build variables like GOARM, GOOS and GOARCH are simply forwarded from the current environment with some default values:

tools/cmd/gokr-packer/gotool.go

Lines 15 to 28 in 7f0229b

	func goEnv() []string {
	goarch := "arm64" // Raspberry Pi 3
	if e := os.Getenv("GOARCH"); e != "" {
	goarch = e
	}
	env := os.Environ()
	for idx, e := range env {
	if strings.HasPrefix(e, "CGO_ENABLED=") {
	env[idx] = "CGO_ENABLED=0"
	}
	}
	return append(env, fmt.Sprintf("GOARCH=%s", goarch))
	}

However this does not play well with go run:

GOARCH=arm go run github.com/gokrazy/tools/cmd/gokr-packer
    github.com/gokrazy/hello

Since GOARCH will be used by go run, the resulting gokr-packer executable will not run on and amd64 machine for instance.

---

I would like to be able to use go run github.com/gokrazy/tools/cmd/gokr-packer, so that the gokr-packer version can be managed by go.mod using a tools.go file:

//go:build tools

package tools

import (
	_ "github.com/gokrazy/tools/cmd/gokr-packer"
)

---

Here are the possible solutions to this problem, that I thought of:

• support prefixed environment variables: GOKR_GOARCH= go run ... for instance (which would override `GOARCH)
• add a flag to support build environment file: go run .../gokr-packer -buildenv=env with env being a file like:

GOARCH=arm

What do you think would be the most elegant way to fix this issue ?
I can then try to craft a PR.

[stapelberg]

Instead of using go run, why not just go install && gokr-packer?

If you absolutely want to use go run, can you use its -exec flag to specify a wrapper that applies environment variables?

I’d like to avoid adding a custom way to pass environment variables.

[oliverpool]

Instead of using go run, why not just go install && gokr-packer?

Because I wasn't able to find gokr-packerafterwards 🙈 it is actually simply in $(go env GOPATH)/bin/gokr-packer...
(and it seems faster than go run)