feature: new rule enforce-switch-default (#1390)

rule/enforce_switch_style.go

@@ -0,0 +1,106 @@
+package rule
+
+import (
+	"fmt"
+	"go/ast"
+
+	"github.com/mgechev/revive/lint"
+)
+
+// EnforceSwitchStyleRule implements a rule to enforce default clauses use and/or position.
+type EnforceSwitchStyleRule struct {
+	allowNoDefault      bool // allow absence of default
+	allowDefaultNotLast bool // allow default, if present, not being the last case
+}
+
+// Configure validates the rule configuration, and configures the rule accordingly.
+//
+// Configuration implements the [lint.ConfigurableRule] interface.
+func (r *EnforceSwitchStyleRule) Configure(arguments lint.Arguments) error {
+	if len(arguments) < 1 {
+		return nil
+	}
+
+	for _, arg := range arguments {
+		argStr, ok := arg.(string)
+		if !ok {
+			return fmt.Errorf("invalid argument for rule %s; expected string but got %T", r.Name(), arg)
+		}
+		switch {
+		case isRuleOption(argStr, "allowNoDefault"):
+			r.allowNoDefault = true
+		case isRuleOption(argStr, "allowDefaultNotLast"):
+			r.allowDefaultNotLast = true
+		default:
+			return fmt.Errorf(`invalid argument %q for rule %s; expected "allowNoDefault" or "allowDefaultNotLast"`, argStr, r.Name())
+		}
+	}
+
+	return nil
+}
+
+// Apply applies the rule to given file.
+func (r *EnforceSwitchStyleRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+	astFile := file.AST
+	ast.Inspect(astFile, func(n ast.Node) bool {
+		switchNode, ok := n.(*ast.SwitchStmt)
+		if !ok {
+			return true // not a switch statement
+		}
+
+		defaultClause, isLast := r.seekDefaultCase(switchNode.Body)
+		hasDefault := defaultClause != nil
+
+		if !hasDefault && r.allowNoDefault {
+			return true // switch without default but the rule is configured to don´t care
+		}
+
+		if !hasDefault && !r.allowNoDefault {
+			// switch without default
+			failures = append(failures, lint.Failure{
+				Confidence: 1,
+				Node:       switchNode,
+				Category:   lint.FailureCategoryStyle,
+				Failure:    "switch must have a default case clause",
+			})
+
+			return true
+		}
+
+		// the switch has a default
+
+		if r.allowDefaultNotLast || isLast {
+			return true
+		}
+
+		failures = append(failures, lint.Failure{
+			Confidence: 1,
+			Node:       defaultClause,
+			Category:   lint.FailureCategoryStyle,
+			Failure:    "default case clause must be the last one",
+		})
+
+		return true
+	})
+
+	return failures
+}
+
+func (*EnforceSwitchStyleRule) seekDefaultCase(body *ast.BlockStmt) (defaultClause *ast.CaseClause, isLast bool) {
+	var last *ast.CaseClause
+	for _, stmt := range body.List {
+		cc, _ := stmt.(*ast.CaseClause) // no need to check for ok
+		last = cc
+		if cc.List == nil { // a nil List means "default"
+			defaultClause = cc
+		}
+	}
+
+	return defaultClause, defaultClause == last
+}
+
+// Name returns the rule name.
+func (*EnforceSwitchStyleRule) Name() string {
+	return "enforce-switch-style"
+}