Refactor Build/describe() with Buildable protocol

Sources/Build/describe().swift

@@ -27,7 +27,9 @@ public func describe(prefix: String, _ conf: Configuration, _ modules: [Module],
     let prefix = try mkdir(prefix, conf.dirname)
     let yaml = try YAML(path: "\(prefix).yaml")
     let write = yaml.write
-    let (tests, nontests) = targetSplitter(modules, products)
+
+    let (buildableTests, buildableNonTests) = (modules.map{$0 as Buildable} + products.map{$0 as Buildable}).partition{$0.isTest}
+    let (tests, nontests) = (buildableTests.map{$0.targetName}, buildableNonTests.map{$0.targetName})
 
     defer { yaml.close() }
 

Sources/Build/misc.swift

@@ -107,17 +107,22 @@ func infoPlist(test: Product) -> String {
     return s
 }
 
-// this function because I couldn't make a Buildable
-// protocol and then implement an isTest function
-// without Swift runtime erroring about "Could not
-// convert Array from Objective-C.
-// FIXME please improve!
-func targetSplitter(modules: [Module], _ products: [Product]) -> ([String], [String]) {
-    let (testmodules, nontestmodules) = modules.partition{ $0 is TestModule }
-    let (testproducts, nontestproducts) = products.partition{ if case .Test = $0.type { return true } else { return false } }
-
-    let one = testmodules.map{$0.targetName} + testproducts.map{$0.targetName}
-    let two = nontestmodules.map{$0.targetName} + nontestproducts.map{$0.targetName}
-
-    return (one, two)
+protocol Buildable {
+    var targetName: String { get }
+    var isTest: Bool { get }
+}
+
+extension Module: Buildable {
+    var isTest: Bool {
+        return self is TestModule
+    }
+}
+
+extension Product: Buildable {
+    var isTest: Bool {
+        if case .Test = type {
+            return true
+        }
+        return false
+    }
 }