imports: add go:generate directive for generating zstdlib.go

Change-Id: I8c54e01799f690819cda746ad5fb7c4d87e769c4
Reviewed-on: https://go-review.googlesource.com/22541
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

imports/imports.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:generate go run mkstdlib.go
+
 // Package imports implements a Go pretty-printer (like package "go/format")
 // that also adds or removes import statements as necessary.
 package imports // import "golang.org/x/tools/imports"

imports/mkstdlib.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"go/format"
 	"io"
+	"io/ioutil"
 	"log"
 	"os"
 	"path"
@@ -90,5 +91,8 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
-	os.Stdout.Write(fmtbuf)
+	err = ioutil.WriteFile("zstdlib.go", fmtbuf, 0666)
+	if err != nil {
+		log.Fatal(err)
+	}
 }