Move all file handling into main.go.

cmd/pgen/gen.go

@@ -1,16 +1,14 @@
 package main
 
 import (
-	"path/filepath"
+	"io"
 	"log"
 	"go/ast"
 	"go/format"
 	"go/parser"
 	"go/token"
 	"golang.org/x/tools/go/ast/astutil"
-	"os"
 	"regexp"
-	"strings"
 )
 
 type subspec struct {
@@ -91,16 +89,6 @@ var (
 )
 
 func init() {
-	fs,err := filepath.Glob("pgen*.go")
-	if err != nil {
-		log.Fatal("Glob error")
-	}
-	for _,f := range(fs) {
-		err := os.Remove(f)
-		if err != nil && os.IsExist(err) {
-			log.Fatal("Removing ",f,err)
-		}
-	}
 	qexp = regexp.MustCompile(`"`)
 }
 
@@ -153,24 +141,15 @@ func (g *Generator) Import(name string) {
 	astutil.AddImport(g.fset, g.nodes, name)
 }
 
-func (g *Generator) Save() {
+func (g *Generator) Save(of io.Writer) {
 	if g.nodes == nil {
 		return
 	}
-	var of *os.File
-	var err error
-	if g.name == "main" {
-		of, err = os.Create("pgen.go")
-	} else {
-		oname := strings.Join([]string{"pgen_",g.name,".go"},"")
-		of, err = os.Create(oname)
+	if g.name != "main" {
 		g.nodes.Name = ast.NewIdent(g.name)
 	}
-	if err != nil {
-		log.Fatal("Cannot open pgen.go")
-	}
 
-	err = format.Node(of,g.fset,g.nodes)
+	err := format.Node(of,g.fset,g.nodes)
 	if err != nil {
 		log.Fatal("Generate error:",err)
 	}

cmd/pgen/main.go

@@ -7,6 +7,8 @@ import (
 	"go/token"
 	"go/types"
 	"log"
+	"os"
+	"path/filepath"
 	"regexp"
 	"strings"
 )
@@ -104,6 +106,18 @@ func init() {
 	imps = make(map[string]string)
 	needImps = make(map[string]bool)
 	fset = token.NewFileSet()
+
+	// clear out old generated files
+	fs,err := filepath.Glob("pgen*.go")
+	if err != nil {
+		log.Fatal("Glob error")
+	}
+	for _,f := range(fs) {
+		err := os.Remove(f)
+		if err != nil && os.IsExist(err) {
+			log.Fatal("Removing ",f,err)
+		}
+	}
 }
 
 func main() {
@@ -116,6 +130,9 @@ func main() {
 		log.Print("Processing package ",pkg.Name)
 		ts = make(map[string]tps)
 		chkpkg(pkg)
+		if len(ts) == 0 {
+			continue
+		}
 		g := NewGenerator(pkg.Name)
 		for _,v := range ts {
 			g.Add(v.fun, v.name, v.typ)
@@ -123,9 +140,20 @@ func main() {
 		for name := range needImps {
 			g.Import(imps[name])
 		}
+		var of *os.File
+		var err error
+		if pkg.Name == "main" {
+			of, err = os.Create("pgen.go")
+		} else {
+			oname := strings.Join([]string{"pgen_",pkg.Name,".go"},"")
+			of, err = os.Create(oname)
+		}
+		if err != nil {
+			log.Fatal("Cannot open output file: ",err)
+		}
 		// process template for each type identified and
 		// generate output
-		g.Save()
+		g.Save(of)
 	}
 }