Add increment decrement

fixtures/increment-decrement.go

@@ -0,0 +1,14 @@
+// Test for use of x++ and x--.
+
+// Package pkg ...
+package pkg
+
+func addOne(x int) int {
+	x += 1 // MATCH /should replace x += 1 with x++/
+	return x
+}
+
+func subOneInLoop(y int) {
+	for ; y > 0; y -= 1 { // MATCH /should replace y -= 1 with y--/
+	}
+}

rule/increment-decrement.go

@@ -0,0 +1,74 @@
+package rule
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+
+	"github.com/mgechev/revive/lint"
+)
+
+// IncrementDecrementRule lints given else constructs.
+type IncrementDecrementRule struct{}
+
+// Apply applies the rule to given file.
+func (r *IncrementDecrementRule) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+
+	fileAst := file.AST
+	walker := lintIncrementDecrement{
+		file: file,
+		onFailure: func(failure lint.Failure) {
+			failures = append(failures, failure)
+		},
+	}
+
+	ast.Walk(walker, fileAst)
+
+	return failures
+}
+
+// Name returns the rule name.
+func (r *IncrementDecrementRule) Name() string {
+	return "increment-decrement"
+}
+
+type lintIncrementDecrement struct {
+	file      *lint.File
+	fileAst   *ast.File
+	onFailure func(lint.Failure)
+}
+
+func (w lintIncrementDecrement) Visit(n ast.Node) ast.Visitor {
+	as, ok := n.(*ast.AssignStmt)
+	if !ok {
+		return w
+	}
+	if len(as.Lhs) != 1 {
+		return w
+	}
+	if !isOne(as.Rhs[0]) {
+		return w
+	}
+	var suffix string
+	switch as.Tok {
+	case token.ADD_ASSIGN:
+		suffix = "++"
+	case token.SUB_ASSIGN:
+		suffix = "--"
+	default:
+		return w
+	}
+	w.onFailure(lint.Failure{
+		Confidence: 0.8,
+		Node:       as,
+		Category:   "unary-op",
+		Failure:    fmt.Sprintf("should replace %s with %s%s", w.file.Render(as), w.file.Render(as.Lhs[0]), suffix),
+	})
+	return w
+}
+
+func isOne(expr ast.Expr) bool {
+	lit, ok := expr.(*ast.BasicLit)
+	return ok && lit.Kind == token.INT && lit.Value == "1"
+}

testutil/lint_test.go

@@ -46,6 +46,7 @@ var rules = []lint.Rule{
 	&rule.ErrorsRule{},
 	&rule.ErrorStringsRule{},
 	&rule.ReceiverNameRule{},
+	&rule.IncrementDecrementRule{},
 }
 
 func TestAll(t *testing.T) {