add NewParser method to create parser from option

cmd/reviewdog/main.go

@@ -106,9 +106,9 @@ func run(r io.Reader, w io.Writer, opt *option) error {
 		return runList(w)
 	}
 
-	p, err := parser(opt)
+	p, err := reviewdog.NewParser(&reviewdog.ParserOpt{FormatName: opt.f, Errorformat: opt.efms})
 	if err != nil {
-		return err
+		return fmt.Errorf("fail to create parser. use either -f or -efm: %v", err)
 	}
 
 	var cs reviewdog.CommentService
@@ -184,30 +184,6 @@ func sortedFmts(fs fmts.Fmts) []*fmts.Fmt {
 	return r
 }
 
-func parser(opt *option) (reviewdog.Parser, error) {
-	if opt.f == "checkstyle" {
-		return reviewdog.NewCheckStyleParser(), nil
-	}
-
-	// use defined errorformat
-	if opt.f != "" {
-		if len(opt.efms) > 0 {
-			return nil, errors.New("you cannot specify both -f and -efm at the same time")
-		}
-		efm, ok := fmts.DefinedFmts()[opt.f]
-		if !ok {
-			return nil, fmt.Errorf("%q is not supported. Use -efm or consider to add new errrorformat to https://github.com/haya14busa/errorformat", opt.f)
-		}
-		opt.efms = efm.Errorformat
-	}
-
-	if len(opt.efms) == 0 {
-		return nil, errors.New("cannot parse input. Please specify -f or -efm")
-	}
-
-	return reviewdog.NewErrorformatParserString(opt.efms)
-}
-
 // FlashCommentService is CommentService which uses Flash method to post comment.
 type FlashCommentService interface {
 	reviewdog.CommentService

parser.go

@@ -2,12 +2,46 @@ package reviewdog
 
 import (
 	"encoding/xml"
+	"errors"
 	"fmt"
 	"io"
 
 	"github.com/haya14busa/errorformat"
+	"github.com/haya14busa/errorformat/fmts"
 )
 
+// ParserOpt represents option to create Parser. Either FormatName or
+// Errorformat should be specified.
+type ParserOpt struct {
+	FormatName  string
+	Errorformat []string
+}
+
+// NewParser returns Parser based on ParserOpt.
+func NewParser(opt *ParserOpt) (Parser, error) {
+	name := opt.FormatName
+
+	if name != "" && len(opt.Errorformat) > 0 {
+		return nil, errors.New("you cannot specify both format name and errorformat at the same time")
+	}
+
+	if name == "checkstyle" {
+		return NewCheckStyleParser(), nil
+	}
+	// use defined errorformat
+	if name != "" {
+		efm, ok := fmts.DefinedFmts()[name]
+		if !ok {
+			return nil, fmt.Errorf("%q is not supported. consider to add new errrorformat to https://github.com/haya14busa/errorformat", name)
+		}
+		opt.Errorformat = efm.Errorformat
+	}
+	if len(opt.Errorformat) == 0 {
+		return nil, errors.New("errorformat is empty")
+	}
+	return NewErrorformatParserString(opt.Errorformat)
+}
+
 var _ Parser = &ErrorformatParser{}
 
 // ErrorformatParser is errorformat parser.

parser_test.go

@@ -1,10 +1,68 @@
 package reviewdog
 
 import (
+	"reflect"
 	"strings"
 	"testing"
 )
 
+func TestNewParser(t *testing.T) {
+	tests := []struct {
+		in      *ParserOpt
+		typ     Parser
+		wantErr bool
+	}{
+		{
+			in: &ParserOpt{
+				FormatName: "checkstyle",
+			},
+			typ: &CheckStyleParser{},
+		},
+		{
+			in: &ParserOpt{
+				FormatName: "golint",
+			},
+			typ: &ErrorformatParser{},
+		},
+		{
+			in: &ParserOpt{
+				Errorformat: []string{`%f:%l:%c:%m`},
+			},
+			typ: &ErrorformatParser{},
+		},
+		{ // empty
+			in:      &ParserOpt{},
+			wantErr: true,
+		},
+		{ // both
+			in: &ParserOpt{
+				FormatName:  "checkstyle",
+				Errorformat: []string{`%f:%l:%c:%m`},
+			},
+			wantErr: true,
+		},
+		{ // unsupported
+			in: &ParserOpt{
+				FormatName: "unsupported format",
+			},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		p, err := NewParser(tt.in)
+		if tt.wantErr && err != nil {
+			continue
+		}
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		if got, want := reflect.TypeOf(p), reflect.TypeOf(tt.typ); got != want {
+			t.Errorf("typ: got %v, want %v", got, want)
+		}
+	}
+}
+
 func TestNewErrorformatParserString(t *testing.T) {
 	in := []string{`%f:%l:%c:%m`, `%-G%.%#`}