build: tidy up print func

Signed-off-by: Justin Chadwell <me@jedevc.com>

build/build.go

@@ -886,9 +886,6 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 					cc := c
 					var printRes map[string][]byte
 					rr, err := c.Build(ctx, so, "buildx", func(ctx context.Context, c gateway.Client) (*gateway.Result, error) {
-						var isFallback bool
-						var origErr error
-						for {
 						if opt.PrintFunc != nil {
 							if _, ok := req.FrontendOpt["frontend.caps"]; !ok {
 								req.FrontendOpt["frontend.caps"] = "moby.buildkit.frontend.subrequests+forward"
@@ -896,38 +893,43 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 								req.FrontendOpt["frontend.caps"] += ",moby.buildkit.frontend.subrequests+forward"
 							}
 							req.FrontendOpt["requestid"] = "frontend." + opt.PrintFunc.Name
-								if isFallback {
-									req.FrontendOpt["build-arg:BUILDKIT_SYNTAX"] = printFallbackImage
-								}
 						}
+
 						res, err := c.Solve(ctx, req)
 						if err != nil {
-								if origErr != nil {
+							fallback := false
-									return nil, err
-								}
 							var reqErr *errdefs.UnsupportedSubrequestError
-								if !isFallback {
 							if errors.As(err, &reqErr) {
 								switch reqErr.Name {
 								case "frontend.outline", "frontend.targets":
-											isFallback = true
+									fallback = true
-											origErr = err
+								default:
-											continue
+									return nil, err
 								}
+							} else {
 								return nil, err
 							}
 							// buildkit v0.8 vendored in Docker 20.10 does not support typed errors
 							if strings.Contains(err.Error(), "unsupported request frontend.outline") || strings.Contains(err.Error(), "unsupported request frontend.targets") {
-										isFallback = true
+								fallback = true
-										origErr = err
-										continue
 							}
+
+							if fallback {
+								fmt.Println("falling back!")
+								req.FrontendOpt["build-arg:BUILDKIT_SYNTAX"] = printFallbackImage
+								res2, err2 := c.Solve(ctx, req)
+								if err2 != nil {
+									return nil, err
 								}
+								res = res2
+							} else {
 								return nil, err
 							}
+						}
 						if opt.PrintFunc != nil {
 							printRes = res.Metadata
 						}
+
 						results.Set(resultKey(dp.driverIndex, k), res)
 						if resultHandleFunc != nil {
 							resultCtx, err := NewResultContext(ctx, cc, so, res)
@@ -938,7 +940,6 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 							}
 						}
 						return res, nil
-						}
 					}, ch)
 					if err != nil {
 						return err