CI: add the grabpl build-backend command into the repo (#52673)

* Move the grabpl build-backend command and clean it up a bit

pkg/build/droneutil/docs.go

@@ -0,0 +1,2 @@
+// Package droneutil provides utility functions for working with Drone.
+package droneutil

pkg/build/droneutil/event.go

@@ -0,0 +1,34 @@
+package droneutil
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+// Lookup is the equivalent of os.LookupEnv,  but also accepts a list of strings rather than only checking os.Environ()
+func Lookup(values []string, val string) (string, bool) {
+	for _, v := range values {
+		prefix := val + "="
+		if strings.HasPrefix(v, prefix) {
+			return strings.TrimPrefix(v, prefix), true
+		}
+	}
+
+	return "", false
+}
+
+// GetDroneEvent looks for the "DRONE_BUILD_EVENT" in the provided env list and returns the value.
+// if it was not found, then an error is returned.
+func GetDroneEvent(env []string) (string, error) {
+	event, ok := Lookup(env, "DRONE_BUILD_EVENT")
+	if !ok {
+		return "", fmt.Errorf("failed to get DRONE_BUILD_EVENT environmental variable")
+	}
+	return event, nil
+}
+
+// GetDroneEventFromEnv returns the value of DRONE_BUILD_EVENT from os.Environ()
+func GetDroneEventFromEnv() (string, error) {
+	return GetDroneEvent(os.Environ())
+}

pkg/build/droneutil/event_test.go

@@ -0,0 +1,36 @@
+package droneutil_test
+
+import (
+	"testing"
+
+	"github.com/grafana/grafana/pkg/build/droneutil"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetDroneEvent(t *testing.T) {
+	t.Run("Should return the Drone Event", func(t *testing.T) {
+		env := []string{"DRONE_BUILD_EVENT=pull_request"}
+		droneEvent, err := droneutil.GetDroneEvent(env)
+		require.NoError(t, err)
+		require.Equal(t, droneEvent, "pull_request")
+	})
+	t.Run("Should return error, Drone Event env var is missing", func(t *testing.T) {
+		droneEvent, err := droneutil.GetDroneEvent([]string{})
+		require.Error(t, err)
+		require.Empty(t, droneEvent)
+	})
+}
+
+func TestLookup(t *testing.T) {
+	env := []string{"", "EXAMPLE_KEY=value", "EXAMPLE_KEY"}
+	t.Run("A valid lookup should return a string and no error", func(t *testing.T) {
+		val, ok := droneutil.Lookup(env, "EXAMPLE_KEY")
+		require.True(t, ok)
+		require.Equal(t, val, "value")
+	})
+
+	t.Run("An invalid lookup should return an error", func(t *testing.T) {
+		_, ok := droneutil.Lookup(env, "EXAMPLE_KEY_DOES_NOT_EXIST")
+		require.False(t, ok)
+	})
+}