IDE: Support for reconstruction of generic parameter types

Mostly fixes the rest of <rdar://problem/36132173>, but we still
need to correctly reconstruct dependent member types. That's no longer
related to the original problem of subscripts not working though.

Author: slavapestov

lib/IDE/TypeReconstruction.cpp

@@ -2106,6 +2106,25 @@ VisitNodeWeak(ASTContext *ast,
   }
 }
 
+static void
+VisitNodeGenericParam(ASTContext *ast,
+                      Demangle::NodePointer cur_node,
+                      VisitNodeResult &result) {
+  if (cur_node->getNumChildren() == 2) {
+    auto first = cur_node->getChild(0);
+    auto second = cur_node->getChild(1);
+    if (first->getKind() == Demangle::Node::Kind::Index &&
+        second->getKind() == Demangle::Node::Kind::Index) {
+      result._types.push_back(
+        GenericTypeParamType::get(first->getIndex(),
+                                  second->getIndex(), *ast));
+      return;
+    }
+  }
+
+  result._error = "bad generic param type";
+}
+
 static void VisitFirstChildNode(
     ASTContext *ast,
     Demangle::NodePointer cur_node, VisitNodeResult &result) {
@@ -2275,6 +2294,10 @@ static void VisitNode(
     VisitNodeWeak(ast, node, result);
     break;
 
+  case Demangle::Node::Kind::DependentGenericParamType:
+    VisitNodeGenericParam(ast, node, result);
+    break;
+
   case Demangle::Node::Kind::LocalDeclName:
   case Demangle::Node::Kind::Identifier:
   case Demangle::Node::Kind::PrivateDeclName:

test/IDE/reconstruct_type_from_mangled_name.swift

@@ -282,3 +282,27 @@ struct HasSubscript {
     set {}
   }
 }
+
+// FIXME
+// CHECK: decl: FAILURE	for 'T' usr=s:14swift_ide_test19HasGenericSubscriptV1Txmfp
+struct HasGenericSubscript<T> {
+  // CHECK: subscript<U>(t: T) -> U { get set }	for 'subscript' usr=s:14swift_ide_test19HasGenericSubscriptVyqd__xclui
+  // FIXME
+  // CHECK: decl: FAILURE	for 'U'
+  // FIXME
+  // CHECK: decl: FAILURE	for 't'
+  subscript<U>(_ t: T) -> U {
+
+    // CHECK: decl: get {}	for '' usr=s:14swift_ide_test19HasGenericSubscriptVyqd__xcluig
+    // FIXME
+    // CHECK: dref: FAILURE	for 't'
+    get {
+      return t as! U
+    }
+
+    // FIXME
+    // CHECK: dref: FAILURE	for 'U'
+    // CHECK: decl: set {}	for '' usr=s:14swift_ide_test19HasGenericSubscriptVyqd__xcluis
+    set {}
+  }
+}