Checkstyle support (#95)

Implement checkstyle printer

Author: mxpv

Diff for: README.md

@@ -231,7 +231,7 @@ Usage:
   golangci-lint run [flags]
 
 Flags:
-      --out-format string           Format of output: colored-line-number|line-number|json|tab (default "colored-line-number")
+      --out-format string           Format of output: colored-line-number|line-number|json|tab|checkstyle (default "colored-line-number")
       --print-issued-lines          Print lines of code with issue (default true)
       --print-linter-name           Print linter name in issue line (default true)
       --issues-exit-code int        Exit code when issues were found (default 1)

Diff for: pkg/commands/run.go

@@ -256,6 +256,8 @@ func (e *Executor) runAndPrint(ctx context.Context, args []string) error {
 			format == config.OutFormatColoredLineNumber, e.cfg.Output.PrintLinterName)
 	case config.OutFormatTab:
 		p = printers.NewTab(e.cfg.Output.PrintLinterName)
+	case config.OutFormatCheckstyle:
+		p = printers.NewCheckstyle()
 	default:
 		return fmt.Errorf("unknown output format %s", format)
 	}

Diff for: pkg/config/config.go

@@ -11,9 +11,16 @@ const (
 	OutFormatLineNumber        = "line-number"
 	OutFormatColoredLineNumber = "colored-line-number"
 	OutFormatTab               = "tab"
+	OutFormatCheckstyle        = "checkstyle"
 )
 
-var OutFormats = []string{OutFormatColoredLineNumber, OutFormatLineNumber, OutFormatJSON, OutFormatTab}
+var OutFormats = []string{
+	OutFormatColoredLineNumber,
+	OutFormatLineNumber,
+	OutFormatJSON,
+	OutFormatTab,
+	OutFormatCheckstyle,
+}
 
 type ExcludePattern struct {
 	Pattern string

Diff for: pkg/printers/checkstyle.go

@@ -0,0 +1,78 @@
+package printers
+
+import (
+	"context"
+	"encoding/xml"
+	"fmt"
+
+	"github.com/golangci/golangci-lint/pkg/result"
+)
+
+type checkstyleOutput struct {
+	XMLName xml.Name          `xml:"checkstyle"`
+	Version string            `xml:"version,attr"`
+	Files   []*checkstyleFile `xml:"file"`
+}
+
+type checkstyleFile struct {
+	Name   string             `xml:"name,attr"`
+	Errors []*checkstyleError `xml:"error"`
+}
+
+type checkstyleError struct {
+	Column   int    `xml:"column,attr"`
+	Line     int    `xml:"line,attr"`
+	Message  string `xml:"message,attr"`
+	Severity string `xml:"severity,attr"`
+	Source   string `xml:"source,attr"`
+}
+
+const defaultSeverity = "error"
+
+type Checkstyle struct{}
+
+func NewCheckstyle() *Checkstyle {
+	return &Checkstyle{}
+}
+
+func (Checkstyle) Print(ctx context.Context, issues <-chan result.Issue) (bool, error) {
+	out := checkstyleOutput{
+		Version: "5.0",
+	}
+
+	files := map[string]*checkstyleFile{}
+
+	for issue := range issues {
+		file, ok := files[issue.FilePath()]
+		if !ok {
+			file = &checkstyleFile{
+				Name: issue.FilePath(),
+			}
+
+			files[issue.FilePath()] = file
+		}
+
+		newError := &checkstyleError{
+			Column:   issue.Column(),
+			Line:     issue.Line(),
+			Message:  issue.Text,
+			Source:   issue.FromLinter,
+			Severity: defaultSeverity,
+		}
+
+		file.Errors = append(file.Errors, newError)
+	}
+
+	out.Files = make([]*checkstyleFile, 0, len(files))
+	for _, file := range files {
+		out.Files = append(out.Files, file)
+	}
+
+	data, err := xml.Marshal(&out)
+	if err != nil {
+		return false, err
+	}
+
+	fmt.Fprintf(StdOut, "%s%s\n", xml.Header, data)
+	return len(files) > 0, nil
+}

Diff for: pkg/result/issue.go

@@ -23,6 +23,10 @@ func (i Issue) Line() int {
 	return i.Pos.Line
 }
 
+func (i Issue) Column() int {
+	return i.Pos.Column
+}
+
 func (i Issue) GetLineRange() Range {
 	if i.LineRange == nil {
 		return Range{