Move source files to where SPM expectes them to be

Sources/Stencil/Context.swift

@@ -0,0 +1,88 @@
+/// A container for template variables.
+public class Context {
+  var dictionaries: [[String: Any?]]
+
+  /// The context's environment, such as registered extensions, classes, …
+  public let environment: Environment
+
+  /// Create a context from a dictionary (and an env.)
+  ///
+  /// - Parameters:
+  ///   - dictionary: The context's data
+  ///   - environment: Environment such as extensions, …
+  public init(dictionary: [String: Any] = [:], environment: Environment? = nil) {
+    if !dictionary.isEmpty {
+      dictionaries = [dictionary]
+    } else {
+      dictionaries = []
+    }
+
+    self.environment = environment ?? Environment()
+  }
+
+  /// Access variables in this context by name
+  public subscript(key: String) -> Any? {
+    /// Retrieves a variable's value, starting at the current context and going upwards
+    get {
+      for dictionary in Array(dictionaries.reversed()) {
+        if let value = dictionary[key] {
+          return value
+        }
+      }
+
+      return nil
+    }
+
+    /// Set a variable in the current context, deleting the variable if it's nil
+    set(value) {
+      if var dictionary = dictionaries.popLast() {
+        dictionary[key] = value
+        dictionaries.append(dictionary)
+      }
+    }
+  }
+
+  /// Push a new level into the Context
+  ///
+  /// - Parameters:
+  ///   - dictionary: The new level data
+  fileprivate func push(_ dictionary: [String: Any] = [:]) {
+    dictionaries.append(dictionary)
+  }
+
+  /// Pop the last level off of the Context
+  ///
+  /// - returns: The popped level
+  fileprivate func pop() -> [String: Any?]? {
+    dictionaries.popLast()
+  }
+
+  /// Push a new level onto the context for the duration of the execution of the given closure
+  ///
+  /// - Parameters:
+  ///   - dictionary: The new level data
+  ///   - closure: The closure to execute
+  /// - returns: Return value of the closure
+  public func push<Result>(dictionary: [String: Any] = [:], closure: (() throws -> Result)) rethrows -> Result {
+    push(dictionary)
+    defer { _ = pop() }
+    return try closure()
+  }
+
+  /// Flatten all levels of context data into 1, merging duplicate variables
+  /// 
+  /// - returns: All collected variables
+  public func flatten() -> [String: Any] {
+    var accumulator: [String: Any] = [:]
+
+    for dictionary in dictionaries {
+      for (key, value) in dictionary {
+        if let value = value {
+          accumulator.updateValue(value, forKey: key)
+        }
+      }
+    }
+
+    return accumulator
+  }
+}