Add support for child configs

Sourcery/Configuration.swift

@@ -183,7 +183,7 @@ public struct Package {
         })
         semaphore.wait()
 
-        guard let manifest = try manifestResult?.get() else{
+        guard let manifest = try manifestResult?.get() else {
             throw Configuration.Error.invalidSources(message: "Unable to load manifest")
         }
         self.root = path
@@ -227,6 +227,8 @@ public enum Source {
         } else if let packages = (dict["package"] as? [[String: Any]]) ?? (dict["package"] as? [String: Any]).map({ [$0] }) {
             guard !packages.isEmpty else { throw Configuration.Error.invalidSources(message: "No packages provided.") }
             self = try .packages(packages.map({ try Package(dict: $0, relativePath: relativePath) }))
+        } else if dict["child"] != nil {
+            throw Configuration.Error.internalError(message: "'child' should have been parsed already.")
         } else {
             throw Configuration.Error.invalidSources(message: "'sources', 'project' or 'package' key are missing.")
         }
@@ -315,6 +317,7 @@ public struct Configuration {
         case invalidOutput(message: String)
         case invalidCacheBasePath(message: String)
         case invalidPaths(message: String)
+        case internalError(message: String)
 
         public var description: String {
             switch self {
@@ -332,6 +335,8 @@ public struct Configuration {
                 return "Invalid cacheBasePath. \(message)"
             case .invalidPaths(let message):
                 return "\(message)"
+            case .internalError(let message):
+                return "\(message)"
             }
         }
     }
@@ -431,8 +436,14 @@ public enum Configurations {
         }
 
         if let configurations = dict["configurations"] as? [[String: Any]] {
-            return try configurations.map { dict in
-                try Configuration(dict: dict, relativePath: relativePath)
+            return try configurations.flatMap { dict in
+                if let child = dict["child"] as? String {
+                    let childPath = Path(child, relativeTo: relativePath)
+                    let childRelativePath = Path(components: childPath.components.dropLast())
+                    return try Configurations.make(path: childPath, relativePath: childRelativePath, env: env)
+                } else {
+                    return try [Configuration(dict: dict, relativePath: relativePath)]
+                }
             }
         } else {
             return try [Configuration(dict: dict, relativePath: relativePath)]

SourceryTests/ConfigurationSpec.swift

@@ -86,6 +86,33 @@ class ConfigurationSpec: QuickSpec {
                 }
             }
 
+            context("given config file with child configurations") {
+                it("resolves each child configuration") {
+                    do {
+                        let configs = try Configurations.make(
+                            path: Stubs.configs + "parent.yml",
+                            relativePath: Stubs.configs,
+                            env: env
+                        )
+
+                        expect(configs.count).to(equal(1))
+
+                        guard case let Source.sources(paths) = configs[0].source,
+                              let path = paths.include.first else {
+                            fail("Config has no Source Paths")
+                            return
+                        }
+
+                        let configServerUrl = configs[0].args[serverUrlArg] as? String
+
+                        expect(configServerUrl).to(equal(serverUrl))
+                        expect(path).to(equal(Stubs.configs))
+                    } catch {
+                        expect("\(error)").to(equal("Invalid config file format. Expected dictionary."))
+                    }
+                }
+            }
+
             context("given invalid config file") {
 
                 func configError(_ config: [String: Any]) -> String {

SourceryTests/Stub/Configs/parent.yml

@@ -0,0 +1,2 @@
+configurations:
+    - child: valid.yml

guides/Usage.md

@@ -78,6 +78,16 @@ configurations:
 
 This will be equivalent to running Sourcery separately for each of the configurations. In watch mode Sourcery will observe changes in the paths from all the configurations.
 
+#### Child configurations
+
+You can specify a child configurations by using the `child` key:
+```yaml
+configurations:
+    - child: ./.child_config.yml
+    - child: Subdirectory/.another_child_config.yml
+```
+Sources will be resolved relative to the child config paths.
+
 #### Sources
 
 You can provide sources using paths to directories or specific files.