New formatter: checkstyle (#37)

* Adds rule superfluous-else (an extension of indent-error-flow)

* Fix superfluous-else rule struct namming.

* Adds superfuous-else rule to the rules table

* Adds confusing-naming rule

* adds multifile test

* [WIP] fix multiple file test

* draft solution for detecting confusing-names through multiple files

* [WIP] confusing-name multiple files

* clean-up

* draft working version

* cleaner version + more informative messages

* adds check on struct field names

* fix config.go

* clean master

* new ADS rule: newerr

* ADS-print working version

* ads-print final version

* ads-lost-err working version

* confusing-namming: fix tests

* removes ads-* rules

* Adds checkstyle formatter

* Update README.md

fix typo

README.md

@@ -96,7 +96,8 @@ go get -u github.com/mgechev/revive
   - `ndjson` - outputs the failures as stream in newline delimited JSON (NDJSON) format.
   - `friendly` - outputs the failures when found. Shows summary of all the failures.
   - `stylish` - formats the failures in a table. Keep in mind that it doesn't stream the output so it might be perceived as slower compared to others.
-
+  - `checkstyle` - outputs the failures in XML format compatible with that of Java's [Checkstyle](https://checkstyle.org/).
+  
 ### Sample Invocations
 
 ```shell

config.go

@@ -63,6 +63,7 @@ var allFormatters = []lint.Formatter{
 	&formatter.JSON{},
 	&formatter.NDJSON{},
 	&formatter.Default{},
+	&formatter.Checkstyle{},
 }
 
 func getFormatters() map[string]lint.Formatter {

formatter/checkstyle.go

@@ -0,0 +1,76 @@
+package formatter
+
+import (
+	"bytes"
+	"encoding/xml"
+	"github.com/mgechev/revive/lint"
+	plainTemplate "text/template"
+)
+
+// Checkstyle is an implementation of the Formatter interface
+// which formats the errors to Checkstyle-like format.
+type Checkstyle struct {
+	Metadata lint.FormatterMetadata
+}
+
+// Name returns the name of the formatter
+func (f *Checkstyle) Name() string {
+	return "checkstyle"
+}
+
+type issue struct {
+	Line       int
+	Col        int
+	What       string
+	Confidence float64
+	Severity   lint.Severity
+	RuleName   string
+}
+
+// Format formats the failures gotten from the lint.
+func (f *Checkstyle) Format(failures <-chan lint.Failure, config lint.RulesConfig) (string, error) {
+	var issues = map[string][]issue{}
+	for failure := range failures {
+		buf := new(bytes.Buffer)
+		xml.Escape(buf, []byte(failure.Failure))
+		what := buf.String()
+		iss := issue{
+			Line:       failure.Position.Start.Line,
+			Col:        failure.Position.Start.Column,
+			What:       what,
+			Confidence: failure.Confidence,
+			Severity:   severity(config, failure),
+			RuleName:   failure.RuleName,
+		}
+		fn := failure.GetFilename()
+		if issues[fn] == nil {
+			issues[fn] = make([]issue, 0)
+		}
+		issues[fn] = append(issues[fn], iss)
+	}
+
+	t, err := plainTemplate.New("revive").Parse(checkstyleTemplate)
+	if err != nil {
+		return "", err
+	}
+
+	buf := new(bytes.Buffer)
+
+	err = t.Execute(buf, issues)
+	if err != nil {
+		return "", err
+	}
+
+	return buf.String(), nil
+}
+
+const checkstyleTemplate = `<?xml version='1.0' encoding='UTF-8'?>
+<checkstyle version="5.0">
+{{- range $k, $v := . }}
+    <file name="{{ $k }}">
+      {{- range $i, $issue := $v }}
+      <error line="{{ $issue.Line }}" column="{{ $issue.Col }}" message="{{ $issue.What }} (confidence {{ $issue.Confidence}})" severity="{{ $issue.Severity }}" source="revive/{{ $issue.RuleName }}"/>
+      {{- end }}
+    </file>
+{{- end }}
+</checkstyle>`