new rule: nested-structs (#530)

new rule: nested-structs

rule/nested-structs.go

@@ -0,0 +1,61 @@
+package rule
+
+import (
+	"go/ast"
+
+	"github.com/mgechev/revive/lint"
+)
+
+// NestedStructs lints nested structs.
+type NestedStructs struct{}
+
+// Apply applies the rule to given file.
+func (r *NestedStructs) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+
+	if len(arguments) > 0 {
+		panic(r.Name() + " doesn't take any arguments")
+	}
+
+	walker := &lintNestedStructs{
+		fileAST: file.AST,
+		onFailure: func(failure lint.Failure) {
+			failures = append(failures, failure)
+		},
+	}
+
+	ast.Walk(walker, file.AST)
+
+	return failures
+}
+
+// Name returns the rule name.
+func (r *NestedStructs) Name() string {
+	return "nested-structs"
+}
+
+type lintNestedStructs struct {
+	fileAST   *ast.File
+	onFailure func(lint.Failure)
+}
+
+func (l *lintNestedStructs) Visit(n ast.Node) ast.Visitor {
+	switch v := n.(type) {
+	case *ast.FuncDecl:
+		if v.Body != nil {
+			ast.Walk(l, v.Body)
+		}
+		return nil
+	case *ast.Field:
+		if _, ok := v.Type.(*ast.StructType); ok {
+			l.onFailure(lint.Failure{
+				Failure:    "no nested structs are allowed",
+				Category:   "style",
+				Node:       v,
+				Confidence: 1,
+			})
+			break
+		}
+	}
+	return l
+}