go gen improvements (#524)

Remove the "gen" directory and move directives_generate.go out of it.
Add a build ignore tag so it isn't build by default. Cleanup the go gen
invocations so there are not seen as package docs.

Simplify the code a bit and don't run go gen twice.

Makefile

@@ -50,7 +50,7 @@ clean:
 
 .PHONY: gen
 gen:
-	go generate ./core/...
+	go generate coredns.go
 
 .PHONY: distclean
 distclean: clean

core/coredns.go

 // Package core registers the server and all plugins we support.
-
-// Additional middleware packages
-//go:generate go run ../gen/directives_generate.go ../middleware.cfg
 package core
 
 import (

core/dnsserver/directives.go

-//go:generate go run ../../gen/directives_generate.go ../../middleware.cfg
 package dnsserver
 
 import (

core/dnsserver/zdirectives.go

 // generated by directives_generate.go; DO NOT EDIT
 package dnsserver
 
-
 // Directives are registered in the order they should be
 // executed.
 //

coredns.go

 package main
 
+//go:generate go run directives_generate.go
+
 import "github.com/miekg/coredns/coremain"
 
 func main() {

gen/directives_generate.go → directives_generate.go

+//+build ignore
+
 package main
 
 import (
 	"bufio"
+	"go/format"
 	"io/ioutil"
+	"log"
 	"os"
 	"sort"
 	"strconv"
 	"strings"
 )
 
-var middlewarePath = "github.com/miekg/coredns/middleware/"
-var header = "// generated by directives_generate.go; DO NOT EDIT\n"
-
 func main() {
-	mwFile := os.Args[1]
-
 	mi := make(map[string]string, 0)
 	md := make(map[int]string, 0)
 
-	if file, err := os.Open(mwFile); err == nil {
+	file, err := os.Open(middlewareFile)
+	fatalIfErr(err)
+
 	defer file.Close()
 
 	scanner := bufio.NewScanner(file)
@@ -43,48 +44,32 @@ func main() {
 		}
 	}
 
-		var orders []int
-		for k := range md {
-			orders = append(orders, k)
-		}
-		sort.Ints(orders)
-
-		if os.Getenv("GOPACKAGE") == "core" {
-			genImports("zmiddleware.go", mi)
-		}
-		if os.Getenv("GOPACKAGE") == "dnsserver" {
-			genDirectives("zdirectives.go", md)
-		}
-
-	} else {
-		os.Exit(1)
-	}
-	os.Exit(0)
-
+	genImports("core/zmiddleware.go", "core", mi)
+	genDirectives("core/dnsserver/zdirectives.go", "dnsserver", md)
 }
 
-func genImports(file string, mi map[string]string) {
-	outs := header + "package " + os.Getenv("GOPACKAGE") + "\n\n" + "import ("
+func genImports(file, pack string, mi map[string]string) {
+	outs := header + "package " + pack + "\n\n" + "import ("
 
 	if len(mi) > 0 {
 		outs += "\n"
 	}
 
 	for _, v := range mi {
-		outs += "		_ \"" + v + "\"\n"
+		outs += `_ "` + v + `\` + "\n"
 	}
 	outs += ")\n"
 
-	err := ioutil.WriteFile(file, []byte(outs), 0644)
-	if err != nil {
-		os.Exit(1)
-	}
+	res, err := format.Source([]byte(outs))
+	fatalIfErr(err)
 
+	err = ioutil.WriteFile(file, res, 0644)
+	fatalIfErr(err)
 }
 
-func genDirectives(file string, md map[int]string) {
+func genDirectives(file, pack string, md map[int]string) {
 
-	outs := header + "package " + os.Getenv("GOPACKAGE") + "\n\n"
+	outs := header + "package " + pack + "\n\n"
 	outs += `
 // Directives are registered in the order they should be
 // executed.
@@ -104,13 +89,26 @@ var directives = []string{
 	sort.Ints(orders)
 
 	for _, k := range orders {
-		outs += "		\"" + md[k] + "\",\n"
+		outs += `"` + md[k] + `",` + "\n"
 	}
 
 	outs += "}\n"
 
-	err := ioutil.WriteFile(file, []byte(outs), 0644)
+	res, err := format.Source([]byte(outs))
+	fatalIfErr(err)
+
+	err = ioutil.WriteFile(file, res, 0644)
+	fatalIfErr(err)
+}
+
+func fatalIfErr(err error) {
 	if err != nil {
-		os.Exit(1)
+		log.Fatal(err)
 	}
 }
+
+const (
+	middlewarePath = "github.com/miekg/coredns/middleware/"
+	middlewareFile = "middleware.cfg"
+	header         = "// generated by directives_generate.go; DO NOT EDIT\n"
+)