diff --git a/infer/src/base/JsonBuilder.ml b/infer/src/base/JsonBuilder.ml
new file mode 100644
index 000000000..01608ecc5
--- /dev/null
+++ b/infer/src/base/JsonBuilder.ml
@@ -0,0 +1,46 @@
+(*
+ * Copyright (c) 2017 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+open! IStd
+
+type t = {integers: int String.Map.t; floats: float String.Map.t; strings: string String.Map.t}
+
+let empty = {integers= String.Map.empty; floats= String.Map.empty; strings= String.Map.empty}
+
+let add_int ({integers} as t) ~key ~data = {t with integers= String.Map.set integers ~key ~data}
+
+let add_float ({floats} as t) ~key ~data = {t with floats= String.Map.set floats ~key ~data}
+
+let add_string ({strings} as t) ~key ~data = {t with strings= String.Map.set strings ~key ~data}
+
+let add_string_opt t ~key ~data =
+  match data with Some data -> add_string t ~key ~data | None -> t
+
+
+let yojson_of_integers integers =
+  let f ~key ~data acc = (key, `Int data) :: acc in
+  `Assoc (String.Map.fold integers ~init:[] ~f)
+
+
+let yojson_of_floats floats =
+  let f ~key ~data acc = (key, `Float data) :: acc in
+  `Assoc (String.Map.fold floats ~init:[] ~f)
+
+
+let yojson_of_strings strings =
+  let f ~key ~data acc = (key, `String data) :: acc in
+  `Assoc (String.Map.fold strings ~init:[] ~f)
+
+
+let to_json {integers; floats; strings} =
+  `Assoc
+    [ ("int", yojson_of_integers integers)
+    ; ("double", yojson_of_floats floats)
+    ; ("normal", yojson_of_strings strings) ]
+  |> Yojson.Basic.to_string
diff --git a/infer/src/opensource/JsonBuilder.mli b/infer/src/base/JsonBuilder.mli
similarity index 100%
rename from infer/src/opensource/JsonBuilder.mli
rename to infer/src/base/JsonBuilder.mli
diff --git a/infer/src/opensource/JsonBuilder.ml b/infer/src/opensource/JsonBuilder.ml
deleted file mode 100644
index c9352b141..000000000
--- a/infer/src/opensource/JsonBuilder.ml
+++ /dev/null
@@ -1,26 +0,0 @@
-(*
- * Copyright (c) 2017 - present Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *)
-
-open! IStd
-
-type t = (string * Yojson.Basic.json) list
-
-let empty = []
-
-let add_int t ~key ~data = (key, `Int data) :: t
-
-let add_float t ~key ~data = (key, `Float data) :: t
-
-let add_string t ~key ~data = (key, `String data) :: t
-
-let add_string_opt t ~key ~data =
-  match data with Some data -> add_string t ~key ~data | None -> t
-
-
-let to_json t = Yojson.Basic.to_string (`Assoc t)
diff --git a/infer/src/opensource/fbTraceCalls.ml b/infer/src/opensource/fbTraceCalls.ml
deleted file mode 100644
index a54492bbd..000000000
--- a/infer/src/opensource/fbTraceCalls.ml
+++ /dev/null
@@ -1,12 +0,0 @@
-(*
- * Copyright (c) 2016 - present Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *)
-
-open! IStd
-
-let tracing_methods = []
diff --git a/infer/src/opensource/fbTraceCalls.mli b/infer/src/opensource/fbTraceCalls.mli
deleted file mode 100644
index d46a6ffc1..000000000
--- a/infer/src/opensource/fbTraceCalls.mli
+++ /dev/null
@@ -1,12 +0,0 @@
-(*
- * Copyright (c) 2016 - present Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *)
-
-open! IStd
-
-val tracing_methods : (string * string * string * string) list