provisioners/local-exec: stoppable

This modifies local-exec to be stoppable with the new Stop API call that
provisioners can listen to.

builtin/provisioners/local-exec/resource_provisioner.go

@@ -68,8 +68,24 @@ func applyFn(ctx context.Context) error {
 		"Executing: %s %s \"%s\"",
 		shell, flag, command))
 
-	// Run the command to completion
-	err := cmd.Run()
+	// Start the command
+	err := cmd.Start()
+	if err == nil {
+		// Wait for the command to complete in a goroutine
+		doneCh := make(chan struct{})
+		go func() {
+			defer close(doneCh)
+			err = cmd.Wait()
+		}()
+
+		// Wait for the command to finish or for us to be interrupted
+		select {
+		case <-doneCh:
+		case <-ctx.Done():
+			cmd.Process.Kill()
+			err = cmd.Wait()
+		}
+	}
 
 	// Close the write-end of the pipe so that the goroutine mirroring output
 	// ends properly.

builtin/provisioners/local-exec/resource_provisioner_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/hashicorp/terraform/config"
 	"github.com/hashicorp/terraform/terraform"
@@ -35,6 +36,37 @@ func TestResourceProvider_Apply(t *testing.T) {
 	}
 }
 
+func TestResourceProvider_stop(t *testing.T) {
+	c := testConfig(t, map[string]interface{}{
+		"command": "sleep 60",
+	})
+
+	output := new(terraform.MockUIOutput)
+	p := Provisioner()
+
+	var err error
+	doneCh := make(chan struct{})
+	go func() {
+		defer close(doneCh)
+		err = p.Apply(output, nil, c)
+	}()
+
+	select {
+	case <-doneCh:
+		t.Fatal("should not finish quickly")
+	case <-time.After(10 * time.Millisecond):
+	}
+
+	// Stop it
+	p.Stop()
+
+	select {
+	case <-doneCh:
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("should finish")
+	}
+}
+
 func TestResourceProvider_Validate_good(t *testing.T) {
 	c := testConfig(t, map[string]interface{}{
 		"command": "echo foo",