Print warning if a module not present for a product, error out if zer…

Fixtures/Miscellaneous/ProductWithMissingModules/Foo.swift

@@ -0,0 +1,3 @@
+public class Foo {
+    var bar: Int = 0
+}

Fixtures/Miscellaneous/ProductWithMissingModules/Package.swift

@@ -0,0 +1,7 @@
+import PackageDescription
+
+let package = Package(name: "Foo")
+
+let archive = Product(name: "Bar", type: .Library(.Static), modules: "Foo", "Baz")
+
+products.append(archive)

Fixtures/Miscellaneous/ProductWithNoModules/Foo.swift

@@ -0,0 +1,3 @@
+public class Foo {
+    var bar: Int = 0
+}

Fixtures/Miscellaneous/ProductWithNoModules/Package.swift

@@ -0,0 +1,7 @@
+import PackageDescription
+
+let package = Package(name: "Foo")
+
+let archive = Product(name: "Bar", type: .Library(.Dynamic), modules: "")
+
+products.append(archive)

Sources/Transmute/Error.swift

@@ -29,3 +29,9 @@ extension Module {
         case MixedSources(String)
     }
 }
+
+extension Product {
+    public enum Error: ErrorProtocol {
+        case NoModules(String)
+    }
+}

Sources/Transmute/Package+products.swift

@@ -37,10 +37,18 @@ extension Package {
     ////// add products from the manifest
 
         for p in manifest.products {
-            //FIXME no bang
-            let modules = p.modules.map{ moduleName in
-                modules.pick{ $0.name == moduleName } as! SwiftModule
+            let modules: [SwiftModule] = p.modules.flatMap{ moduleName in
+                guard case let picked as SwiftModule = (modules.pick{ $0.name == moduleName }) else {
+                    print("warning: No module \(moduleName) found for product \(p.name)")
+                    return nil
+                }
+                return picked
             }
+
+            guard !modules.isEmpty else {
+                throw Product.Error.NoModules(p.name)
+            }
+
             let product = Product(name: p.name, type: p.type, modules: modules)
             products.append(product)
         }

Tests/Functional/TestMiscellaneous.swift

@@ -349,4 +349,17 @@ class MiscellaneousTestCase: XCTestCase {
             XCTAssertFileExists(prefix, ".build/debug/libBar.a")
         }
     }
+
+    func testProductWithNoModules() {
+        fixture(name: "Miscellaneous/ProductWithNoModules") { prefix in
+            XCTAssertBuildFails(prefix)
+        }
+    }
+
+    func testProductWithMissingModules() {
+        fixture(name: "Miscellaneous/ProductWithMissingModules") { prefix in
+            XCTAssertBuilds(prefix)
+            XCTAssertFileExists(prefix, ".build/debug/libBar.a")
+        }
+    }
 }

Tests/Functional/TestValidLayouts.swift

@@ -181,6 +181,8 @@ extension MiscellaneousTestCase {
             ("testInternalDependencyEdges", testInternalDependencyEdges),
             ("testExternalDependencyEdges1", testExternalDependencyEdges1),
             ("testExternalDependencyEdges2", testExternalDependencyEdges2),
+            ("testProductWithNoModules", testProductWithNoModules),
+            ("testProductWithMissingModules", testProductWithMissingModules),
         ]
     }
 }