fix cyclical target dependencies

Sources/XcodeGenKit/PBXProjGenerator.swift

@@ -456,15 +456,25 @@ public class PBXProjGenerator {
         return "\(carthagePath)/\(platformName)"
     }
 
-    func getAllCarthageDependencies(target: Target) -> [Dependency] {
+    func getAllCarthageDependencies(target: Target, visitedTargets: [String: Bool] = [:]) -> [Dependency] {
+
+        // this is used to resolve cyclical target dependencies
+        var visitedTargets = visitedTargets
+        visitedTargets[target.name] = true
+
         var frameworks: [Dependency] = []
+
         for dependency in target.dependencies {
             switch dependency.type {
             case .carthage:
                 frameworks.append(dependency)
             case .target:
-                if let target = spec.getTarget(dependency.reference) {
-                    frameworks += getAllCarthageDependencies(target: target)
+                let targetName = dependency.reference
+                if visitedTargets[targetName] == true {
+                    return []
+                }
+                if let target = spec.getTarget(targetName) {
+                    frameworks += getAllCarthageDependencies(target: target, visitedTargets: visitedTargets)
                 }
             default: break
             }

Tests/XcodeGenKitTests/ProjectGeneratorTests.swift

@@ -13,7 +13,6 @@ func projectGeneratorTests() {
     }
 
     func getPbxProj(_ spec: ProjectSpec) throws -> PBXProj {
-        try spec.validate()
         let project = try getProject(spec).pbxproj
         try project.validate()
         return project
@@ -171,6 +170,14 @@ func projectGeneratorTests() {
                 try expect(script1.shellScript) == "script1"
                 try expect(script2.shellScript) == "script2"
             }
+
+            $0.it("generates targets with cylical dependencies") {
+                let target1 = Target(name: "target1", type: .framework, platform: .iOS, dependencies: [Dependency(type: .target, reference: "target2")])
+                let target2 = Target(name: "target2", type: .framework, platform: .iOS, dependencies: [Dependency(type: .target, reference: "target1")])
+                let spec = ProjectSpec(basePath: "", name: "test", targets: [target1, target2])
+
+                _ = try getPbxProj(spec)
+            }
         }
 
         $0.describe("Schemes") {