From 34674018ef627e917b41f2e262280e9377e3d4fe Mon Sep 17 00:00:00 2001
From: Dmitri Shuralyov <shurcooL@gmail.com>
Date: Sat, 30 May 2015 23:43:49 -0700
Subject: [PATCH] gopherjs serve: Display compilation errors in browser
 console.

This is nice when using with gopherjs serve, because it already
recompiles on browser refresh. This allows one to switch between code
editor and browser for a faster iteration cycle. No need to also switch
to the terminal to see errors, as now both compilation and runtime
errors are visible in browser console.
---
 tool.go | 43 +++++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/tool.go b/tool.go
index fcee9bd5a..ea4ef87ea 100644
--- a/tool.go
+++ b/tool.go
@@ -125,7 +125,7 @@ func main() {
 					}
 				}
 				return nil
-			}, options)
+			}, options, nil)
 
 			if s.Watcher == nil {
 				os.Exit(exitCode)
@@ -184,7 +184,7 @@ func main() {
 					}
 				}
 				return nil
-			}, options)
+			}, options, nil)
 
 			if s.Watcher == nil {
 				os.Exit(exitCode)
@@ -238,7 +238,7 @@ func main() {
 				return err
 			}
 			return nil
-		}, options))
+		}, options, nil))
 	}
 
 	cmdTest := &cobra.Command{
@@ -394,7 +394,7 @@ func main() {
 				fmt.Printf("%s\t%s\t%.3fs\n", status, pkg.ImportPath, time.Now().Sub(start).Seconds())
 			}
 			return exitErr
-		}, options))
+		}, options, nil))
 	}
 
 	cmdTool := &cobra.Command{
@@ -422,7 +422,7 @@ func main() {
 			}
 			cmdTool.Help()
 			return nil
-		}, options))
+		}, options, nil))
 	}
 
 	cmdServe := &cobra.Command{
@@ -485,7 +485,8 @@ func (fs serveCommandFileSystem) Open(name string) (http.File, error) {
 
 		if isMain {
 			buf := bytes.NewBuffer(nil)
-			handleError(func() error {
+			browserErrors := bytes.NewBuffer(nil)
+			exitCode := handleError(func() error {
 				pkg := &gbuild.PackageData{Package: buildPkg}
 				if err := s.BuildPackage(pkg); err != nil {
 					return err
@@ -509,7 +510,10 @@ func (fs serveCommandFileSystem) Open(name string) (http.File, error) {
 				fs.sourceMaps[name+".map"] = mapBuf.Bytes()
 
 				return nil
-			}, fs.options)
+			}, fs.options, browserErrors)
+			if exitCode != 0 {
+				buf = browserErrors
+			}
 			return newFakeFile("main.js", buf.Bytes()), nil
 		}
 	}
@@ -563,24 +567,26 @@ func (f *fakeFile) Sys() interface{} {
 	return nil
 }
 
-func handleError(f func() error, options *gbuild.Options) int {
+// If browserErrors is non-nil, errors are written for presentation in browser.
+func handleError(f func() error, options *gbuild.Options, browserErrors *bytes.Buffer) int {
 	switch err := f().(type) {
 	case nil:
 		return 0
 	case compiler.ErrorList:
 		for _, entry := range err {
-			printError(entry, options)
+			printError(entry, options, browserErrors)
 		}
 		return 1
 	case *exec.ExitError:
 		return err.Sys().(syscall.WaitStatus).ExitStatus()
 	default:
-		printError(err, options)
+		printError(err, options, browserErrors)
 		return 1
 	}
 }
 
-func printError(err error, options *gbuild.Options) {
+// sprintError returns an annotated error string without trailing newline.
+func sprintError(err error) string {
 	makeRel := func(name string) string {
 		if relname, err := filepath.Rel(currentDirectory, name); err == nil {
 			return relname
@@ -590,12 +596,21 @@ func printError(err error, options *gbuild.Options) {
 
 	switch e := err.(type) {
 	case *scanner.Error:
-		options.PrintError("%s:%d:%d: %s\n", makeRel(e.Pos.Filename), e.Pos.Line, e.Pos.Column, e.Msg)
+		return fmt.Sprintf("%s:%d:%d: %s", makeRel(e.Pos.Filename), e.Pos.Line, e.Pos.Column, e.Msg)
 	case types.Error:
 		pos := e.Fset.Position(e.Pos)
-		options.PrintError("%s:%d:%d: %s\n", makeRel(pos.Filename), pos.Line, pos.Column, e.Msg)
+		return fmt.Sprintf("%s:%d:%d: %s", makeRel(pos.Filename), pos.Line, pos.Column, e.Msg)
 	default:
-		options.PrintError("%s\n", e)
+		return fmt.Sprintf("%s", e)
+	}
+}
+
+// printError prints err to Stderr with options. If browserErrors is non-nil, errors are also written for presentation in browser.
+func printError(err error, options *gbuild.Options, browserErrors *bytes.Buffer) {
+	e := sprintError(err)
+	options.PrintError("%s\n", e)
+	if browserErrors != nil {
+		fmt.Fprintln(browserErrors, `console.error("`+template.JSEscapeString(e)+`");`)
 	}
 }