feat: Add KO_GO_PATH env var

docs/configuration.md

@@ -2,9 +2,8 @@
 
 ## Basic Configuration
 
-Aside from `KO_DOCKER_REPO`, you can configure `ko`'s behavior using a
-`.ko.yaml` file. The location of this file can be overridden with
-`KO_CONFIG_PATH`.
+Aside from certain environment variables (see [below](#environment-variables-advanced)) like `KO_DOCKER_REPO`, you can
+configure `ko`'s behavior using a `.ko.yaml` file. The location of this file can be overridden with `KO_CONFIG_PATH`.
 
 ### Overriding Base Images
 
@@ -83,7 +82,6 @@ The `ldflags` default value is `[]`.
 only the `env`, `flags` and `ldflags` fields are currently supported. Also, the
 templating support is currently limited to using environment variables only.
 
-
 ### Setting default platforms
 
 By default, `ko` builds images based on the platform it runs on. If your target platform differs from your build platform you can specify the build platform:
@@ -106,6 +104,18 @@ You can also use the `KO_DEFAULTPLATFORMS` environment variable to set the defau
 KO_DEFAULTPLATFORMS=linux/arm64,linux/amd64
 ```
 
+### Environment Variables (advanced)
+
+For ease of use, backward compatibility and advanced use cases, `ko` supports the following environment variables to
+influence the build process.
+
+| Variable         | Default Value                              | Description                                                                                                                                                                                                                      |
+|------------------|--------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `KO_DOCKER_REPO` | (not set)                                  | Container repository where to push images built with `ko` (required)                                                                                                                                                             |
+| `KO_DATA_PATH`   | `/var/run/ko` (`C:\var\run\ko` on Windows) | By convention, any contents of a directory named `<importpath>/kodata/` will be bundled into the image, and the path where it's available in the image will be identified by the environment variable `KO_DATA_PATH` (optional). |
+| `KO_GO_PATH`     | `go`                                       | `go` binary to use for builds, relative or absolute path, otherwise looked up via $PATH (optional)                                                                                                                               |
+| `KO_CONFIG_PATH` | `./ko.yaml`                                | Path to `ko` configuration file (optional)                                                                                                                                                                                       |
+| `KOCACHE`        | (not set)                                  | This tells `ko` to store a local mapping between the `go build` inputs to the image layer that they produce, so `go build` can be skipped entirely if the layer is already present in the image registry (optional).             |
 
 ## Naming Images
 

pkg/build/cache.go

@@ -201,7 +201,9 @@ func (c *layerCache) readBuildToDiff(file string) (buildIDToDiffID, error) {
 }
 
 func getBuildID(ctx context.Context, file string) (string, error) {
-	cmd := exec.CommandContext(ctx, "go", "tool", "buildid", file)
+	gobin := getGoBinary()
+
+	cmd := exec.CommandContext(ctx, gobin, "tool", "buildid", file)
 	var output bytes.Buffer
 	cmd.Stderr = &output
 	cmd.Stdout = &output

pkg/build/gobuild.go

@@ -56,6 +56,9 @@ import (
 
 const (
 	defaultAppFilename = "ko-app"
+
+	defaultGoBin = "go"         // defaults to first go binary found in PATH
+	goBinPathEnv = "KO_GO_PATH" // env lookup for optional relative or full go binary path
 )
 
 // GetBase takes an importpath and returns a base image reference and base image (or index).
@@ -244,6 +247,13 @@ func getGoarm(platform v1.Platform) (string, error) {
 	return "", nil
 }
 
+func getGoBinary() string {
+	if env := os.Getenv(goBinPathEnv); env != "" {
+		return env
+	}
+	return defaultGoBin
+}
+
 func build(ctx context.Context, ip string, dir string, platform v1.Platform, config Config) (string, error) {
 	buildArgs, err := createBuildArgs(config)
 	if err != nil {
@@ -285,7 +295,9 @@ func build(ctx context.Context, ip string, dir string, platform v1.Platform, con
 
 	args = append(args, "-o", file)
 	args = append(args, ip)
-	cmd := exec.CommandContext(ctx, "go", args...)
+
+	gobin := getGoBinary()
+	cmd := exec.CommandContext(ctx, gobin, args...)
 	cmd.Dir = dir
 	cmd.Env = env
 
@@ -305,10 +317,12 @@ func build(ctx context.Context, ip string, dir string, platform v1.Platform, con
 }
 
 func goversionm(ctx context.Context, file string, appPath string, appFileName string, se oci.SignedEntity, dir string) ([]byte, types.MediaType, error) {
+	gobin := getGoBinary()
+
 	switch se.(type) {
 	case oci.SignedImage:
 		sbom := bytes.NewBuffer(nil)
-		cmd := exec.CommandContext(ctx, "go", "version", "-m", file)
+		cmd := exec.CommandContext(ctx, gobin, "version", "-m", file)
 		cmd.Stdout = sbom
 		cmd.Stderr = os.Stderr
 		if err := cmd.Run(); err != nil {