Adds new rule empty-block (#14)

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

* initial (non functional) version

* empty-block working version

* adds tests for empty-block rule

* Adds empty-block to the rules table

* code clean-up

rule/empty-block.go

@@ -0,0 +1,52 @@
+package rule
+
+import (
+	"go/ast"
+
+	"github.com/mgechev/revive/lint"
+)
+
+// EmptyBlockRule lints given else constructs.
+type EmptyBlockRule struct{}
+
+// Apply applies the rule to given file.
+func (r *EmptyBlockRule) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+
+	onFailure := func(failure lint.Failure) {
+		failures = append(failures, failure)
+	}
+
+	w := lintEmptyBlock{make(map[*ast.IfStmt]bool), onFailure}
+	ast.Walk(w, file.AST)
+	return failures
+}
+
+// Name returns the rule name.
+func (r *EmptyBlockRule) Name() string {
+	return "empty-block"
+}
+
+type lintEmptyBlock struct {
+	ignore    map[*ast.IfStmt]bool
+	onFailure func(lint.Failure)
+}
+
+func (w lintEmptyBlock) Visit(node ast.Node) ast.Visitor {
+	block, ok := node.(*ast.BlockStmt)
+	if !ok {
+		return w
+	}
+
+	if len(block.List) == 0 {
+		w.onFailure(lint.Failure{
+			Confidence: 1,
+			Node:       block,
+			Category:   "logic",
+			URL:        "#empty-block",
+			Failure:    "this block is empty, you can remove it",
+		})
+	}
+
+	return w
+}