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/P4Compiler/Common.swift

@@ -120,6 +120,30 @@ extension ParameterList: Compilable {
   }
 }
 
+extension Direction: Compilable {
+  public typealias T = Direction
+  public static func Compile(
+    node: Node, withContext context: CompilerContext
+  ) -> Result<(Direction, CompilerContext)> {
+    let direction_node = node
+    #RequireNodeType<Node, (Direction, CompilerContext)>(
+      node: direction_node, type: "direction", nice_type_name: "direction")
+    let directions = [
+      "in": Direction.In,
+      "out": Direction.Out,
+      "inout": Direction.InOut,
+    ]
+
+    guard let parsed_direction = directions[direction_node.text!] else {
+      return .Error(
+        ErrorOnNode(
+          node: direction_node, withError: "\(direction_node.text!) is not a valid direction"))
+    }
+
+    return .Ok((parsed_direction, context))
+  }
+}
+
 extension Parameter: Compilable {
   public typealias T = Parameter
   public static func Compile(
@@ -148,15 +172,22 @@ extension Parameter: Compilable {
           withError: "Annotations in parameter declarations are not yet handled"))
       // Will increment indexes here.
     }
+    currentChild = node.child(at: currentChildIdx)
 
+    var direction: Direction? = .none
     // Direction?
     if currentChild!.nodeType == "direction" {
-      return .Error(
-        ErrorOnNode(
-          node: currentChild!, withError: "Direction in parameter declarations are not yet handled"
-        ))
-      // Will increment indexes here.
+
+      let maybe_parsed_direction = Direction.Compile(node: currentChild!, withContext: context)
+      guard case .Ok((let parsed_direction, _)) = maybe_parsed_direction else {
+        return .Error(maybe_parsed_direction.error()!)
+      }
+      direction = parsed_direction
+
+      currentChildIdx += 1
+      currentChildIdxSafe += 1
     }
+    currentChild = node.child(at: currentChildIdx)
 
     if currentChild!.nodeType != "typeRef" {
       return Result.Error(
@@ -195,7 +226,7 @@ extension Parameter: Compilable {
     return Result.Ok(
       (
         Parameter(
-          identifier: parameter_name, withType: parameter_type),
+          identifier: parameter_name, withType: parameter_type, withDirection: direction),
         context
       ))
   }