From 15e5684884b282ac116ad7007e63e0862929c505 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Fri, 4 Oct 2024 14:56:43 +0200
Subject: [PATCH] experimental-features.hh: Don't include json-utils.hh

This caused nlohmann/json.hpp to leak into a lot of compilation units,
which is slow (when not using precompiled headers).

Cuts build time from 46m24s to 42m5s (real time with -j24: 2m42s to
2m24s).
---
 src/libexpr/primops/fetchTree.cc                 | 2 ++
 src/libfetchers/git.cc                           | 2 +-
 src/libflake/flake/flake.cc                      | 2 ++
 src/libstore/derivations.cc                      | 5 +++--
 src/libstore/local-store.cc                      | 2 ++
 src/libstore/nar-info.cc                         | 1 +
 src/libutil/config-global.cc                     | 2 ++
 src/libutil/experimental-features.hh             | 9 ++-------
 src/libutil/json-utils.hh                        | 9 ++++++++-
 src/nix/main.cc                                  | 1 +
 tests/unit/libstore/derivation-advanced-attrs.cc | 2 +-
 11 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index 1004d79ee..d2266e2bc 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -11,6 +11,8 @@
 #include "value-to-json.hh"
 #include "fetch-to-store.hh"
 
+#include <nlohmann/json.hpp>
+
 #include <ctime>
 #include <iomanip>
 #include <regex>
diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 5c6b3d3cc..99d91919e 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -13,8 +13,8 @@
 #include "git-utils.hh"
 #include "logging.hh"
 #include "finally.hh"
-
 #include "fetch-settings.hh"
+#include "json-utils.hh"
 
 #include <regex>
 #include <string.h>
diff --git a/src/libflake/flake/flake.cc b/src/libflake/flake/flake.cc
index 35db13f7e..d18e01464 100644
--- a/src/libflake/flake/flake.cc
+++ b/src/libflake/flake/flake.cc
@@ -13,6 +13,8 @@
 #include "value-to-json.hh"
 #include "local-fs-store.hh"
 
+#include <nlohmann/json.hpp>
+
 namespace nix {
 
 using namespace flake;
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 8f9c71851..9b6f67852 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -7,11 +7,12 @@
 #include "split.hh"
 #include "common-protocol.hh"
 #include "common-protocol-impl.hh"
+#include "strings-inline.hh"
+#include "json-utils.hh"
+
 #include <boost/container/small_vector.hpp>
 #include <nlohmann/json.hpp>
 
-#include "strings-inline.hh"
-
 namespace nix {
 
 std::optional<StorePath> DerivationOutput::path(const StoreDirConfig & store, std::string_view drvName, OutputNameView outputName) const
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 7d6c82b03..eafdac0cd 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -50,6 +50,8 @@
 
 #include <sqlite3.h>
 
+#include <nlohmann/json.hpp>
+
 #include "strings.hh"
 
 
diff --git a/src/libstore/nar-info.cc b/src/libstore/nar-info.cc
index 2442a7b09..8b2557060 100644
--- a/src/libstore/nar-info.cc
+++ b/src/libstore/nar-info.cc
@@ -2,6 +2,7 @@
 #include "nar-info.hh"
 #include "store-api.hh"
 #include "strings.hh"
+#include "json-utils.hh"
 
 namespace nix {
 
diff --git a/src/libutil/config-global.cc b/src/libutil/config-global.cc
index 4c08898a4..3ed1dd1d3 100644
--- a/src/libutil/config-global.cc
+++ b/src/libutil/config-global.cc
@@ -1,5 +1,7 @@
 #include "config-global.hh"
 
+#include <nlohmann/json.hpp>
+
 namespace nix {
 
 bool GlobalConfig::set(const std::string & name, const std::string & value)
diff --git a/src/libutil/experimental-features.hh b/src/libutil/experimental-features.hh
index e65e51280..412bf0886 100644
--- a/src/libutil/experimental-features.hh
+++ b/src/libutil/experimental-features.hh
@@ -2,9 +2,10 @@
 ///@file
 
 #include "error.hh"
-#include "json-utils.hh"
 #include "types.hh"
 
+#include <nlohmann/json_fwd.hpp>
+
 namespace nix {
 
 /**
@@ -98,10 +99,4 @@ public:
 void to_json(nlohmann::json &, const ExperimentalFeature &);
 void from_json(const nlohmann::json &, ExperimentalFeature &);
 
-/**
- * It is always rendered as a string
- */
-template<>
-struct json_avoids_null<ExperimentalFeature> : std::true_type {};
-
 }
diff --git a/src/libutil/json-utils.hh b/src/libutil/json-utils.hh
index fe7a406cf..a61c9cada 100644
--- a/src/libutil/json-utils.hh
+++ b/src/libutil/json-utils.hh
@@ -3,12 +3,13 @@
 
 #include <nlohmann/json.hpp>
 #include <list>
-#include <nlohmann/json_fwd.hpp>
 
 #include "types.hh"
 
 namespace nix {
 
+enum struct ExperimentalFeature;
+
 const nlohmann::json * get(const nlohmann::json & map, const std::string & key);
 
 nlohmann::json * get(nlohmann::json & map, const std::string & key);
@@ -71,6 +72,12 @@ struct json_avoids_null<std::list<T>> : std::true_type {};
 template<typename K, typename V>
 struct json_avoids_null<std::map<K, V>> : std::true_type {};
 
+/**
+ * `ExperimentalFeature` is always rendered as a string.
+ */
+template<>
+struct json_avoids_null<ExperimentalFeature> : std::true_type {};
+
 }
 
 namespace nlohmann {
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 7a9516d5e..eff2d60a4 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -19,6 +19,7 @@
 #include "eval-cache.hh"
 #include "flake/flake.hh"
 #include "self-exe.hh"
+#include "json-utils.hh"
 
 #include <sys/types.h>
 #include <regex>
diff --git a/tests/unit/libstore/derivation-advanced-attrs.cc b/tests/unit/libstore/derivation-advanced-attrs.cc
index 4d839ddab..9d2c64ef3 100644
--- a/tests/unit/libstore/derivation-advanced-attrs.cc
+++ b/tests/unit/libstore/derivation-advanced-attrs.cc
@@ -1,4 +1,3 @@
-#include <nlohmann/json.hpp>
 #include <gtest/gtest.h>
 #include <optional>
 
@@ -9,6 +8,7 @@
 #include "tests/characterization.hh"
 #include "parsed-derivations.hh"
 #include "types.hh"
+#include "json-utils.hh"
 
 namespace nix {