client: simplify Compute logic

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

dagger/client.go

@@ -51,46 +51,40 @@ func NewClient(ctx context.Context, host string) (*Client, error) {
 }
 
 // FIXME: return completed *Env, instead of *Value
-func (c *Client) Compute(ctx context.Context, env *Env) (o *Value, err error) {
+func (c *Client) Compute(ctx context.Context, env *Env) (*Value, error) {
 	lg := log.Ctx(ctx)
-	defer func() {
-		if err != nil {
-			// Expand cue errors to get full details
-			err = cueErr(err)
-		}
-	}()
 
-	// FIXME: merge this into env output.
-	out, err := env.Compiler().EmptyStruct()
-	if err != nil {
-		return nil, err
-	}
-
-	// Spawn Build() goroutine
-	eg, ctx := errgroup.WithContext(ctx)
-	events := make(chan *bk.SolveStatus)
-	outr, outw := io.Pipe()
-
-	// Spawn build function
-	eg.Go(func() error {
-		defer outw.Close()
-		return c.buildfn(ctx, env, events, outw)
-	})
+	eg, gctx := errgroup.WithContext(ctx)
 
 	// Spawn print function
+	var events chan *bk.SolveStatus
 	if os.Getenv("DOCKER_OUTPUT") != "" {
+		events = make(chan *bk.SolveStatus)
 		eg.Go(func() error {
 			dispCtx := context.TODO()
 			return c.dockerprintfn(dispCtx, events, lg)
 		})
 	}
 
-	// Retrieve output
+	// Spawn build function
+	outr, outw := io.Pipe()
+	eg.Go(func() error {
+		defer outw.Close()
+		return c.buildfn(gctx, env, events, outw)
+	})
+
+	// Spawn output retriever
+	var (
+		out *Value
+		err error
+	)
 	eg.Go(func() error {
 		defer outr.Close()
-		return c.outputfn(ctx, outr, out, env.cc)
+		out, err = c.outputfn(gctx, outr, env.cc)
+		return err
 	})
-	return out, eg.Wait()
+
+	return out, cueErr(eg.Wait())
 }
 
 func (c *Client) buildfn(ctx context.Context, env *Env, ch chan *bk.SolveStatus, w io.WriteCloser) error {
@@ -164,9 +158,15 @@ func (c *Client) buildfn(ctx context.Context, env *Env, ch chan *bk.SolveStatus,
 }
 
 // Read tar export stream from buildkit Build(), and extract cue output
-func (c *Client) outputfn(ctx context.Context, r io.Reader, out *Value, cc *Compiler) error {
+func (c *Client) outputfn(ctx context.Context, r io.Reader, cc *Compiler) (*Value, error) {
 	lg := log.Ctx(ctx)
 
+	// FIXME: merge this into env output.
+	out, err := cc.EmptyStruct()
+	if err != nil {
+		return nil, err
+	}
+
 	tr := tar.NewReader(r)
 	for {
 		h, err := tr.Next()
@@ -174,7 +174,7 @@ func (c *Client) outputfn(ctx context.Context, r io.Reader, out *Value, cc *Comp
 			break
 		}
 		if err != nil {
-			return errors.Wrap(err, "read tar stream")
+			return nil, errors.Wrap(err, "read tar stream")
 		}
 
 		lg := lg.
@@ -190,13 +190,13 @@ func (c *Client) outputfn(ctx context.Context, r io.Reader, out *Value, cc *Comp
 
 		v, err := cc.Compile(h.Name, tr)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		if err := out.Fill(v); err != nil {
-			return errors.Wrap(err, h.Name)
+			return nil, errors.Wrap(err, h.Name)
 		}
 	}
-	return nil
+	return out, nil
 }
 
 func (c *Client) dockerprintfn(ctx context.Context, ch chan *bk.SolveStatus, out io.Writer) error {

dagger/utils.go

@@ -10,6 +10,9 @@ import (
 )
 
 func cueErr(err error) error {
+	if err == nil {
+		return nil
+	}
 	return errors.New(cueerrors.Details(err, &cueerrors.Config{}))
 }