From 45b740c18b196d0326a94df23d08fa3d68e0863f Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 21 Oct 2019 22:11:21 +0200
Subject: [PATCH] Use upstream json_fwd.hpp to speed up compilation

---
 src/libexpr/flake/lockfile.cc      |  2 +
 src/libexpr/flake/lockfile.hh      |  2 +-
 src/libstore/build.cc              |  2 +-
 src/libstore/parsed-derivations.cc |  6 ++-
 src/libstore/parsed-derivations.hh | 10 +++--
 src/nlohmann/json_fwd.hpp          | 66 +++++++++++++++++++++++++++---
 6 files changed, 75 insertions(+), 13 deletions(-)

diff --git a/src/libexpr/flake/lockfile.cc b/src/libexpr/flake/lockfile.cc
index 2c3f3c93d..5693e57dc 100644
--- a/src/libexpr/flake/lockfile.cc
+++ b/src/libexpr/flake/lockfile.cc
@@ -1,6 +1,8 @@
 #include "lockfile.hh"
 #include "store-api.hh"
 
+#include <nlohmann/json.hpp>
+
 namespace nix::flake {
 
 LockedInput::LockedInput(const nlohmann::json & json)
diff --git a/src/libexpr/flake/lockfile.hh b/src/libexpr/flake/lockfile.hh
index ab81eac8b..757c37989 100644
--- a/src/libexpr/flake/lockfile.hh
+++ b/src/libexpr/flake/lockfile.hh
@@ -2,7 +2,7 @@
 
 #include "flakeref.hh"
 
-#include <nlohmann/json.hpp>
+#include <nlohmann/json_fwd.hpp>
 
 namespace nix {
 class Store;
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 21b641f2c..8e795e555 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2521,7 +2521,7 @@ static std::regex shVarName("[A-Za-z_][A-Za-z0-9_]*");
 
 void DerivationGoal::writeStructuredAttrs()
 {
-    auto & structuredAttrs = parsedDrv->getStructuredAttrs();
+    auto structuredAttrs = parsedDrv->getStructuredAttrs();
     if (!structuredAttrs) return;
 
     auto json = *structuredAttrs;
diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index 87be8a24e..5553dd863 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -1,5 +1,7 @@
 #include "parsed-derivations.hh"
 
+#include <nlohmann/json.hpp>
+
 namespace nix {
 
 ParsedDerivation::ParsedDerivation(const Path & drvPath, BasicDerivation & drv)
@@ -9,13 +11,15 @@ ParsedDerivation::ParsedDerivation(const Path & drvPath, BasicDerivation & drv)
     auto jsonAttr = drv.env.find("__json");
     if (jsonAttr != drv.env.end()) {
         try {
-            structuredAttrs = nlohmann::json::parse(jsonAttr->second);
+            structuredAttrs = std::make_unique<nlohmann::json>(nlohmann::json::parse(jsonAttr->second));
         } catch (std::exception & e) {
             throw Error("cannot process __json attribute of '%s': %s", drvPath, e.what());
         }
     }
 }
 
+ParsedDerivation::~ParsedDerivation() { }
+
 std::optional<std::string> ParsedDerivation::getStringAttr(const std::string & name) const
 {
     if (structuredAttrs) {
diff --git a/src/libstore/parsed-derivations.hh b/src/libstore/parsed-derivations.hh
index 9bde4b4dc..6e67e1665 100644
--- a/src/libstore/parsed-derivations.hh
+++ b/src/libstore/parsed-derivations.hh
@@ -1,6 +1,6 @@
 #include "derivations.hh"
 
-#include <nlohmann/json.hpp>
+#include <nlohmann/json_fwd.hpp>
 
 namespace nix {
 
@@ -8,15 +8,17 @@ class ParsedDerivation
 {
     Path drvPath;
     BasicDerivation & drv;
-    std::optional<nlohmann::json> structuredAttrs;
+    std::unique_ptr<nlohmann::json> structuredAttrs;
 
 public:
 
     ParsedDerivation(const Path & drvPath, BasicDerivation & drv);
 
-    const std::optional<nlohmann::json> & getStructuredAttrs() const
+    ~ParsedDerivation();
+
+    const nlohmann::json * getStructuredAttrs() const
     {
-        return structuredAttrs;
+        return structuredAttrs.get();
     }
 
     std::optional<std::string> getStringAttr(const std::string & name) const;
diff --git a/src/nlohmann/json_fwd.hpp b/src/nlohmann/json_fwd.hpp
index ae6e4c64f..28fd10d45 100644
--- a/src/nlohmann/json_fwd.hpp
+++ b/src/nlohmann/json_fwd.hpp
@@ -1,10 +1,64 @@
-#pragma once
+#ifndef INCLUDE_NLOHMANN_JSON_FWD_HPP_
+#define INCLUDE_NLOHMANN_JSON_FWD_HPP_
 
-namespace nlohmann {
+#include <cstdint> // int64_t, uint64_t
+#include <map> // map
+#include <memory> // allocator
+#include <string> // string
+#include <vector> // vector
 
-struct json : basic_json<>
+/*!
+@brief namespace for Niels Lohmann
+@see https://github.com/nlohmann
+@since version 1.0.0
+*/
+namespace nlohmann
 {
-    using basic_json<>::basic_json;
-};
+/*!
+@brief default JSONSerializer template argument
 
-}
+This serializer ignores the template arguments and uses ADL
+([argument-dependent lookup](https://en.cppreference.com/w/cpp/language/adl))
+for serialization.
+*/
+template<typename T = void, typename SFINAE = void>
+struct adl_serializer;
+
+template<template<typename U, typename V, typename... Args> class ObjectType =
+         std::map,
+         template<typename U, typename... Args> class ArrayType = std::vector,
+         class StringType = std::string, class BooleanType = bool,
+         class NumberIntegerType = std::int64_t,
+         class NumberUnsignedType = std::uint64_t,
+         class NumberFloatType = double,
+         template<typename U> class AllocatorType = std::allocator,
+         template<typename T, typename SFINAE = void> class JSONSerializer =
+         adl_serializer>
+class basic_json;
+
+/*!
+@brief JSON Pointer
+
+A JSON pointer defines a string syntax for identifying a specific value
+within a JSON document. It can be used with functions `at` and
+`operator[]`. Furthermore, JSON pointers are the base for JSON patches.
+
+@sa [RFC 6901](https://tools.ietf.org/html/rfc6901)
+
+@since version 2.0.0
+*/
+template<typename BasicJsonType>
+class json_pointer;
+
+/*!
+@brief default JSON class
+
+This type is the default specialization of the @ref basic_json class which
+uses the standard template types.
+
+@since version 1.0.0
+*/
+using json = basic_json<>;
+}  // namespace nlohmann
+
+#endif  // INCLUDE_NLOHMANN_JSON_FWD_HPP_