Add a flag to build library only source tree.

Fixes mitchellh#114

go.go

@@ -122,7 +122,7 @@ func GoCrossCompile(opts *CompileOpts) error {
 // GoMainDirs returns the file paths to the packages that are "main"
 // packages, from the list of packages given. The list of packages can
 // include relative paths, the special "..." Go keyword, etc.
-func GoMainDirs(packages []string, GoCmd string) ([]string, error) {
+func GoMainDirs(packages []string, GoCmd string, cmdOnly bool) ([]string, error) {
 	args := make([]string, 0, len(packages)+3)
 	args = append(args, "list", "-f", "{{.Name}}|{{.ImportPath}}")
 	args = append(args, packages...)
@@ -144,9 +144,10 @@ func GoMainDirs(packages []string, GoCmd string) ([]string, error) {
 			continue
 		}
 
-		if parts[0] == "main" {
-			results = append(results, parts[1])
+		if parts[0] != "main" && cmdOnly {
+			continue
 		}
+		results = append(results, parts[1])
 	}
 
 	return results, nil

main.go

@@ -24,7 +24,7 @@ func realMain() int {
 	var tags string
 	var verbose bool
 	var flagGcflags, flagAsmflags string
-	var flagCgo, flagRebuild, flagListOSArch bool
+	var flagCgo, flagRebuild, flagBuildLib, flagListOSArch bool
 	var flagGoCmd string
 	flags := flag.NewFlagSet("gox", flag.ExitOnError)
 	flags.Usage = func() { printUsage() }
@@ -39,6 +39,7 @@ func realMain() int {
 	flags.BoolVar(&verbose, "verbose", false, "verbose")
 	flags.BoolVar(&flagCgo, "cgo", false, "")
 	flags.BoolVar(&flagRebuild, "rebuild", false, "")
+	flags.BoolVar(&flagBuildLib, "build-lib", false, "")
 	flags.BoolVar(&flagListOSArch, "osarch-list", false, "")
 	flags.StringVar(&flagGcflags, "gcflags", "", "")
 	flags.StringVar(&flagAsmflags, "asmflags", "", "")
@@ -95,7 +96,7 @@ func realMain() int {
 	}
 
 	// Get the packages that are in the given paths
-	mainDirs, err := GoMainDirs(packages, flagGoCmd)
+	mainDirs, err := GoMainDirs(packages, flagGoCmd, !flagBuildLib)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Error reading packages: %s", err)
 		return 1
@@ -194,6 +195,7 @@ Options:
   -parallel=-1        Amount of parallelism, defaults to number of CPUs
   -gocmd="go"         Build command, defaults to Go
   -rebuild            Force rebuilding of package that were up to date
+  -build-lib          Force the build of a library package. By default gox only build for main packages.
   -verbose            Verbose mode
 
 Output path template: