Fix panic

Closes #16

intrange.go

@@ -234,15 +234,11 @@ func check(pass *analysis.Pass) func(node ast.Node) {
 func findNExpr(expr ast.Expr) ast.Expr {
 	switch e := expr.(type) {
 	case *ast.CallExpr:
-		if e.Fun.(*ast.Ident).Name != "len" {
-			return nil
+		if fun, ok := e.Fun.(*ast.Ident); ok && fun.Name == "len" && len(e.Args) == 1 {
+			return findNExpr(e.Args[0])
 		}
 
-		if len(e.Args) != 1 {
-			return nil
-		}
-
-		return findNExpr(e.Args[0])
+		return nil
 	case *ast.BasicLit:
 		return nil
 	case *ast.Ident:

testdata/go.mod

@@ -1,3 +1,5 @@
 module github.com/ckaznocha/intrange/testdata
 
 go 1.21
+
+require google.golang.org/protobuf v1.33.0

testdata/go.sum

@@ -0,0 +1,2 @@
+google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
+google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=

testdata/main.go

@@ -1,6 +1,10 @@
 package main
 
-import "testing"
+import (
+	"testing"
+
+	"google.golang.org/protobuf/reflect/protoreflect"
+)
 
 func main() {
 	for i := 2; i < 10; i++ {
@@ -187,3 +191,10 @@ func main() {
 		t2.m[4] = 4
 	}
 }
+
+// https://github.com/ckaznocha/intrange/issues/16
+func issue16(service protoreflect.ServiceDescriptor) {
+	for i := 0; i < service.Methods().Len(); i++ { // want `for loop can be changed to use an integer range \(Go 1\.22\+\)`
+		print(i)
+	}
+}