makebb: add "generate code but do not build" switch

-g will allow the package to generate code but not compile it.

Systems like tamago are not quite in reach for makebb to build just yet.

If the generate directory is empty an error will be returned.

Co-authored-by: Chris Koch <[email protected]>
Signed-off-by: Ronald G. Minnich <[email protected]>
Signed-off-by: Chris Koch <[email protected]>

src/cmd/makebb/makebb.go

@@ -20,6 +20,7 @@ import (
 var (
 	outputPath = flag.String("o", "bb", "Path to compiled busybox binary")
 	genDir     = flag.String("gen-dir", "", "Directory to generate source in")
+	genOnly    = flag.Bool("g", false, "Generate but do not build binaries")
 )
 
 func main() {
@@ -59,6 +60,7 @@ func main() {
 		CommandPaths: flag.Args(),
 		BinaryPath:   o,
 		GoBuildOpts:  bopts,
+		GenerateOnly: *genOnly,
 	}
 	if err := bb.BuildBusybox(opts); err != nil {
 		l.Print(err)
@@ -71,9 +73,11 @@ func main() {
 		} else {
 			l.Fatalf("Preserving bb generated source directory at %s due to error.", tmpDir)
 		}
+	} else if opts.GenerateOnly {
+		l.Printf("Generated source can be found in %s. `cd %s && go build` to build.", tmpDir, filepath.Join(tmpDir, "src/bb.u-root.com/bb"))
 	}
 	// Only remove temp dir if there was no error.
-	if remove {
+	if remove && !opts.GenerateOnly {
 		os.RemoveAll(tmpDir)
 	}
 }

src/pkg/bb/bb.go

@@ -96,6 +96,10 @@ type Opts struct {
 	//
 	// If this is done with GO111MODULE=on,
 	AllowMixedMode bool
+
+	// Generate the tree but don't build it. This is useful for systems
+	// like Tamago which have their own way of building.
+	GenerateOnly bool
 }
 
 // BuildBusybox builds a busybox of many Go commands. opts contains both the
@@ -132,6 +136,9 @@ func BuildBusybox(opts *Opts) (nerr error) {
 		}
 		tmpDir = absDir
 	} else {
+		if opts.GenerateOnly {
+			return fmt.Errorf("GenerateOnly switch requires that the GenSrcDir directory be supplied")
+		}
 		var err error
 		tmpDir, err = ioutil.TempDir("", "bb-")
 		if err != nil {
@@ -218,6 +225,10 @@ func BuildBusybox(opts *Opts) (nerr error) {
 		}
 	}
 
+	if opts.GenerateOnly {
+		return nil
+	}
+
 	// Compile bb.
 	if err := opts.Env.BuildDir(bbDir, opts.BinaryPath, opts.GoBuildOpts); err != nil {
 		if opts.Env.GO111MODULE == "off" || numNoModule > 0 {