refactor (rule/error-return): replace AST walker by iteration over declarations

rule/error_return.go

@@ -13,16 +13,34 @@ type ErrorReturnRule struct{}
 func (*ErrorReturnRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure {
 	var failures []lint.Failure
 
-	fileAst := file.AST
-	walker := lintErrorReturn{
-		file:    file,
-		fileAst: fileAst,
-		onFailure: func(failure lint.Failure) {
-			failures = append(failures, failure)
-		},
-	}
+	for _, decl := range file.AST.Decls {
+		funcDecl, ok := decl.(*ast.FuncDecl)
+		isFunctionWithMoreThanOneResult := ok && funcDecl.Type.Results != nil && len(funcDecl.Type.Results.List) > 1
+		if !isFunctionWithMoreThanOneResult {
+			continue
+		}
+
+		funcResults := funcDecl.Type.Results.List
+		isLastResultError := isIdent(funcResults[len(funcResults)-1].Type, "error")
+		if isLastResultError {
+			continue
+		}
 
-	ast.Walk(walker, fileAst)
+		// An error return parameter should be the last parameter.
+		// Flag any error parameters found before the last.
+		for _, r := range funcResults[:len(funcResults)-1] {
+			if isIdent(r.Type, "error") {
+				failures = append(failures, lint.Failure{
+					Category:   "style",
+					Confidence: 0.9,
+					Node:       funcDecl,
+					Failure:    "error should be the last type when returning multiple items",
+				})
+
+				break // only flag one
+			}
+		}
+	}
 
 	return failures
 }
@@ -31,37 +49,3 @@ func (*ErrorReturnRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure
 func (*ErrorReturnRule) Name() string {
 	return "error-return"
 }
-
-type lintErrorReturn struct {
-	file      *lint.File
-	fileAst   *ast.File
-	onFailure func(lint.Failure)
-}
-
-func (w lintErrorReturn) Visit(n ast.Node) ast.Visitor {
-	fn, ok := n.(*ast.FuncDecl)
-	if !ok || fn.Type.Results == nil {
-		return w
-	}
-	ret := fn.Type.Results.List
-	if len(ret) <= 1 {
-		return w
-	}
-	if isIdent(ret[len(ret)-1].Type, "error") {
-		return nil
-	}
-	// An error return parameter should be the last parameter.
-	// Flag any error parameters found before the last.
-	for _, r := range ret[:len(ret)-1] {
-		if isIdent(r.Type, "error") {
-			w.onFailure(lint.Failure{
-				Category:   "arg-order",
-				Confidence: 0.9,
-				Node:       fn,
-				Failure:    "error should be the last type when returning multiple items",
-			})
-			break // only flag one
-		}
-	}
-	return w
-}