compiler, runtime, common, testing: Support Directions on Parameters and Attributed Types

Add support for directions on parameters and attributed types. The
latter is necessary to support the former, but is not limited to
the direction use case. An attributed type is a P4 type with attributes
(like its direction, whether it is read only, etc.) Other attributes
will be added in the future.

Changes necessary to support attributed types include:
1. Global instances tracked during compilation are not attributed
types and not simply types.
2. (future) Type checking will have to make sure that a types
attributes do not affect type compatibility.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Sources/P4Lang/Common.swift

@@ -19,21 +19,35 @@ import Common
 
 public struct Parameter: CustomStringConvertible, Equatable {
   public static func == (lhs: Parameter, rhs: Parameter) -> Bool {
-    return lhs.name == rhs.name && lhs.type.eq(rhs: rhs.type)
+    return lhs.name == rhs.name && lhs.type.eq(rhs: rhs.type) && lhs.direction == rhs.direction
   }
 
   public var name: Identifier
   public var type: P4Type
+  public var direction: Direction?
 
   public init(
-    identifier: Identifier, withType type: P4Type
+    identifier: Identifier, withType type: P4Type, withDirection direction: Direction? = .none
   ) {
     self.name = identifier
     self.type = type
+    self.direction = direction
   }
 
   public var description: String {
-    return "Parameter: \(self.name) with type \(self.type)"
+    let direction = self.direction != .none ? self.direction!.description : "no"
+    return "Parameter: \(self.name) with type \(self.type) with \(direction) direction"
+  }
+
+  /// Calculate whether the `argument` is compatible with this parameter.
+  public func compatible(_ argument: Argument) -> Bool {
+    let arg_type = argument.argument.type()
+    return arg_type.eq(rhs: self.type)
+  }
+
+  public func attributedType() -> P4TypeAttributed {
+    return P4TypeAttributed(
+      self.type, self.direction == .none ? [] : [P4TypeAttribute.Direction(self.direction!)])
   }
 }
 
@@ -89,7 +103,7 @@ public struct ArgumentList {
     for (arg, param) in zip(self.arguments, parameters.parameters) {
       let arg_index = arg.index
       let arg_type = arg.argument.type()
-      if !arg_type.eq(rhs: param.type) {
+      if !param.compatible(arg) {
         return .Error(
           Error(
             withMessage: