Merge pull request #7313 from yorickvP/nlohmann-everywhere

Replace src/libutil/json.cc with nlohmann

25 files changed, 266 insertions, 858 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 6ba44cc1d..c759acc10 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -7,7 +7,6 @@
 #include "globals.hh"
 #include "eval-inline.hh"
 #include "filetransfer.hh"
-#include "json.hh"
 #include "function-trace.hh"
 
 #include <algorithm>
@@ -21,6 +20,7 @@
 #include <functional>
 
 #include <sys/resource.h>
+#include <nlohmann/json.hpp>
 
 #if HAVE_BOEHMGC
 
@@ -35,6 +35,8 @@
 
 #endif
 
+using json = nlohmann::json;
+
 namespace nix {
 
 static char * allocString(size_t size)
@@ -2437,97 +2439,97 @@ void EvalState::printStats()
         std::fstream fs;
         if (outPath != "-")
             fs.open(outPath, std::fstream::out);
-        JSONObject topObj(outPath == "-" ? std::cerr : fs, true);
-        topObj.attr("cpuTime",cpuTime);
-        {
-            auto envs = topObj.object("envs");
-            envs.attr("number", nrEnvs);
-            envs.attr("elements", nrValuesInEnvs);
-            envs.attr("bytes", bEnvs);
-        }
-        {
-            auto lists = topObj.object("list");
-            lists.attr("elements", nrListElems);
-            lists.attr("bytes", bLists);
-            lists.attr("concats", nrListConcats);
-        }
-        {
-            auto values = topObj.object("values");
-            values.attr("number", nrValues);
-            values.attr("bytes", bValues);
-        }
-        {
-            auto syms = topObj.object("symbols");
-            syms.attr("number", symbols.size());
-            syms.attr("bytes", symbols.totalSize());
-        }
-        {
-            auto sets = topObj.object("sets");
-            sets.attr("number", nrAttrsets);
-            sets.attr("bytes", bAttrsets);
-            sets.attr("elements", nrAttrsInAttrsets);
-        }
-        {
-            auto sizes = topObj.object("sizes");
-            sizes.attr("Env", sizeof(Env));
-            sizes.attr("Value", sizeof(Value));
-            sizes.attr("Bindings", sizeof(Bindings));
-            sizes.attr("Attr", sizeof(Attr));
-        }
-        topObj.attr("nrOpUpdates", nrOpUpdates);
-        topObj.attr("nrOpUpdateValuesCopied", nrOpUpdateValuesCopied);
-        topObj.attr("nrThunks", nrThunks);
-        topObj.attr("nrAvoided", nrAvoided);
-        topObj.attr("nrLookups", nrLookups);
-        topObj.attr("nrPrimOpCalls", nrPrimOpCalls);
-        topObj.attr("nrFunctionCalls", nrFunctionCalls);
+        json topObj = json::object();
+        topObj["cpuTime"] = cpuTime;
+        topObj["envs"] = {
+            {"number", nrEnvs},
+            {"elements", nrValuesInEnvs},
+            {"bytes", bEnvs},
+        };
+        topObj["list"] = {
+            {"elements", nrListElems},
+            {"bytes", bLists},
+            {"concats", nrListConcats},
+        };
+        topObj["values"] = {
+            {"number", nrValues},
+            {"bytes", bValues},
+        };
+        topObj["symbols"] = {
+            {"number", symbols.size()},
+            {"bytes", symbols.totalSize()},
+        };
+        topObj["sets"] = {
+            {"number", nrAttrsets},
+            {"bytes", bAttrsets},
+            {"elements", nrAttrsInAttrsets},
+        };
+        topObj["sizes"] = {
+            {"Env", sizeof(Env)},
+            {"Value", sizeof(Value)},
+            {"Bindings", sizeof(Bindings)},
+            {"Attr", sizeof(Attr)},
+        };
+        topObj["nrOpUpdates"] = nrOpUpdates;
+        topObj["nrOpUpdateValuesCopied"] = nrOpUpdateValuesCopied;
+        topObj["nrThunks"] = nrThunks;
+        topObj["nrAvoided"] = nrAvoided;
+        topObj["nrLookups"] = nrLookups;
+        topObj["nrPrimOpCalls"] = nrPrimOpCalls;
+        topObj["nrFunctionCalls"] = nrFunctionCalls;
 #if HAVE_BOEHMGC
-        {
-            auto gc = topObj.object("gc");
-            gc.attr("heapSize", heapSize);
-            gc.attr("totalBytes", totalBytes);
-        }
+        topObj["gc"] = {
+            {"heapSize", heapSize},
+            {"totalBytes", totalBytes},
+        };
 #endif
 
         if (countCalls) {
+            topObj["primops"] = primOpCalls;
             {
-                auto obj = topObj.object("primops");
-                for (auto & i : primOpCalls)
-                    obj.attr(i.first, i.second);
-            }
-            {
-                auto list = topObj.list("functions");
+                auto& list = topObj["functions"];
+                list = json::array();
                 for (auto & [fun, count] : functionCalls) {
-                    auto obj = list.object();
+                    json obj = json::object();
                     if (fun->name)
-                        obj.attr("name", (std::string_view) symbols[fun->name]);
+                        obj["name"] = (std::string_view) symbols[fun->name];
                     else
-                        obj.attr("name", nullptr);
+                        obj["name"] = nullptr;
                     if (auto pos = positions[fun->pos]) {
-                        obj.attr("file", (std::string_view) pos.file);
-                        obj.attr("line", pos.line);
-                        obj.attr("column", pos.column);
+                        obj["file"] = (std::string_view) pos.file;
+                        obj["line"] = pos.line;
+                        obj["column"] = pos.column;
                     }
-                    obj.attr("count", count);
+                    obj["count"] = count;
+                    list.push_back(obj);
                 }
             }
             {
-                auto list = topObj.list("attributes");
+                auto list = topObj["attributes"];
+                list = json::array();
                 for (auto & i : attrSelects) {
-                    auto obj = list.object();
+                    json obj = json::object();
                     if (auto pos = positions[i.first]) {
-                        obj.attr("file", (const std::string &) pos.file);
-                        obj.attr("line", pos.line);
-                        obj.attr("column", pos.column);
+                        obj["file"] = (const std::string &) pos.file;
+                        obj["line"] = pos.line;
+                        obj["column"] = pos.column;
                     }
-                    obj.attr("count", i.second);
+                    obj["count"] = i.second;
+                    list.push_back(obj);
                 }
             }
         }
 
         if (getEnv("NIX_SHOW_SYMBOLS").value_or("0") != "0") {
-            auto list = topObj.list("symbols");
-            symbols.dump([&](const std::string & s) { list.elem(s); });
+            // XXX: overrides earlier assignment
+            topObj["symbols"] = json::array();
+            auto &list = topObj["symbols"];
+            symbols.dump([&](const std::string & s) { list.emplace_back(s); });
+        }
+        if (outPath == "-") {
+            std::cerr << topObj.dump(2) << std::endl;
+        } else {
+            fs << topObj.dump(2) << std::endl;
         }
     }
 }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 22f6ad3cc..05265411c 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -8,12 +8,12 @@
 #include "references.hh"
 #include "store-api.hh"
 #include "util.hh"
-#include "json.hh"
 #include "value-to-json.hh"
 #include "value-to-xml.hh"
 #include "primops.hh"
 
 #include <boost/container/small_vector.hpp>
+#include <nlohmann/json.hpp>
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -1011,6 +1011,7 @@ static void prim_second(EvalState & state, const PosIdx pos, Value * * args, Val
    derivation. */
 static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
+    using nlohmann::json;
     state.forceAttrs(*args[0], pos);
 
     /* Figure out the name first (for stack backtraces). */
@@ -1032,11 +1033,10 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
     }
 
     /* Check whether attributes should be passed as a JSON file. */
-    std::ostringstream jsonBuf;
-    std::unique_ptr<JSONObject> jsonObject;
+    std::optional<json> jsonObject;
     attr = args[0]->attrs->find(state.sStructuredAttrs);
     if (attr != args[0]->attrs->end() && state.forceBool(*attr->value, pos))
-        jsonObject = std::make_unique<JSONObject>(jsonBuf);
+        jsonObject = json::object();
 
     /* Check whether null attributes should be ignored. */
     bool ignoreNulls = false;
@@ -1138,8 +1138,7 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
 
                     if (i->name == state.sStructuredAttrs) continue;
 
-                    auto placeholder(jsonObject->placeholder(key));
-                    printValueAsJSON(state, true, *i->value, pos, placeholder, context);
+                    (*jsonObject)[key] = printValueAsJSON(state, true, *i->value, pos, context);
 
                     if (i->name == state.sBuilder)
                         drv.builder = state.forceString(*i->value, context, posDrvName);
@@ -1183,8 +1182,8 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
     }
 
     if (jsonObject) {
+        drv.env.emplace("__json", jsonObject->dump());
         jsonObject.reset();
-        drv.env.emplace("__json", jsonBuf.str());
     }
 
     /* Everything in the context of the strings in the derivation
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index 4d63d8b49..5dc453b2e 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -1,84 +1,82 @@
 #include "value-to-json.hh"
-#include "json.hh"
 #include "eval-inline.hh"
 #include "util.hh"
 
 #include <cstdlib>
 #include <iomanip>
+#include <nlohmann/json.hpp>
 
 
 namespace nix {
-
-void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, JSONPlaceholder & out, PathSet & context, bool copyToStore)
+using json = nlohmann::json;
+json printValueAsJSON(EvalState & state, bool strict,
+    Value & v, const PosIdx pos, PathSet & context, bool copyToStore)
 {
     checkInterrupt();
 
     if (strict) state.forceValue(v, pos);
 
+    json out;
+
     switch (v.type()) {
 
         case nInt:
-            out.write(v.integer);
+            out = v.integer;
             break;
 
         case nBool:
-            out.write(v.boolean);
+            out = v.boolean;
             break;
 
         case nString:
             copyContext(v, context);
-            out.write(v.string.s);
+            out = v.string.s;
             break;
 
         case nPath:
             if (copyToStore)
-                out.write(state.copyPathToStore(context, v.path));
+                out = state.copyPathToStore(context, v.path);
             else
-                out.write(v.path);
+                out = v.path;
             break;
 
         case nNull:
-            out.write(nullptr);
             break;
 
         case nAttrs: {
             auto maybeString = state.tryAttrsToString(pos, v, context, false, false);
             if (maybeString) {
-                out.write(*maybeString);
+                out = *maybeString;
                 break;
             }
             auto i = v.attrs->find(state.sOutPath);
             if (i == v.attrs->end()) {
-                auto obj(out.object());
+                out = json::object();
                 StringSet names;
                 for (auto & j : *v.attrs)
                     names.emplace(state.symbols[j.name]);
                 for (auto & j : names) {
                     Attr & a(*v.attrs->find(state.symbols.create(j)));
-                    auto placeholder(obj.placeholder(j));
-                    printValueAsJSON(state, strict, *a.value, a.pos, placeholder, context, copyToStore);
+                    out[j] = printValueAsJSON(state, strict, *a.value, a.pos, context, copyToStore);
                 }
             } else
-                printValueAsJSON(state, strict, *i->value, i->pos, out, context, copyToStore);
+                return printValueAsJSON(state, strict, *i->value, i->pos, context, copyToStore);
             break;
         }
 
         case nList: {
-            auto list(out.list());
-            for (auto elem : v.listItems()) {
-                auto placeholder(list.placeholder());
-                printValueAsJSON(state, strict, *elem, pos, placeholder, context, copyToStore);
-            }
+            out = json::array();
+            for (auto elem : v.listItems())
+                out.push_back(printValueAsJSON(state, strict, *elem, pos, context, copyToStore));
             break;
         }
 
         case nExternal:
-            v.external->printValueAsJSON(state, strict, out, context, copyToStore);
+            return v.external->printValueAsJSON(state, strict, context, copyToStore);
             break;
 
         case nFloat:
-            out.write(v.fpoint);
+            out = v.fpoint;
             break;
 
         case nThunk:
@@ -91,17 +89,17 @@ void printValueAsJSON(EvalState & state, bool strict,
             state.debugThrowLastTrace(e);
             throw e;
     }
+    return out;
 }
 
 void printValueAsJSON(EvalState & state, bool strict,
     Value & v, const PosIdx pos, std::ostream & str, PathSet & context, bool copyToStore)
 {
-    JSONPlaceholder out(str);
-    printValueAsJSON(state, strict, v, pos, out, context, copyToStore);
+    str << printValueAsJSON(state, strict, v, pos, context, copyToStore);
 }
 
-void ExternalValueBase::printValueAsJSON(EvalState & state, bool strict,
-    JSONPlaceholder & out, PathSet & context, bool copyToStore) const
+json ExternalValueBase::printValueAsJSON(EvalState & state, bool strict,
+    PathSet & context, bool copyToStore) const
 {
     state.debugThrowLastTrace(TypeError("cannot convert %1% to JSON", showType()));
 }
diff --git a/src/libexpr/value-to-json.hh b/src/libexpr/value-to-json.hh
index 7ddc8a5b1..22f26b790 100644
--- a/src/libexpr/value-to-json.hh
+++ b/src/libexpr/value-to-json.hh
@@ -5,13 +5,12 @@
 
 #include <string>
 #include <map>
+#include <nlohmann/json_fwd.hpp>
 
 namespace nix {
 
-class JSONPlaceholder;
-
-void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, JSONPlaceholder & out, PathSet & context, bool copyToStore = true);
+nlohmann::json printValueAsJSON(EvalState & state, bool strict,
+    Value & v, const PosIdx pos, PathSet & context, bool copyToStore = true);
 
 void printValueAsJSON(EvalState & state, bool strict,
     Value & v, const PosIdx pos, std::ostream & str, PathSet & context, bool copyToStore = true);
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index 590ba7783..5adac72f8 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -7,6 +7,7 @@
 #if HAVE_BOEHMGC
 #include <gc/gc_allocator.h>
 #endif
+#include <nlohmann/json_fwd.hpp>
 
 namespace nix {
 
@@ -62,7 +63,6 @@ class StorePath;
 class Store;
 class EvalState;
 class XMLWriter;
-class JSONPlaceholder;
 
 
 typedef int64_t NixInt;
@@ -98,8 +98,8 @@ class ExternalValueBase
     virtual bool operator ==(const ExternalValueBase & b) const;
 
     /* Print the value as JSON. Defaults to unconvertable, i.e. throws an error */
-    virtual void printValueAsJSON(EvalState & state, bool strict,
-        JSONPlaceholder & out, PathSet & context, bool copyToStore = true) const;
+    virtual nlohmann::json printValueAsJSON(EvalState & state, bool strict,
+        PathSet & context, bool copyToStore = true) const;
 
     /* Print the value as XML. Defaults to unevaluated */
     virtual void printValueAsXML(EvalState & state, bool strict, bool location,
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index a26770c79..12d0c32fb 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -9,7 +9,6 @@
 #include "remote-fs-accessor.hh"
 #include "nar-info-disk-cache.hh"
 #include "nar-accessor.hh"
-#include "json.hh"
 #include "thread-pool.hh"
 #include "callback.hh"
 
@@ -194,19 +193,12 @@ ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
     /* Optionally write a JSON file containing a listing of the
        contents of the NAR. */
     if (writeNARListing) {
-        std::ostringstream jsonOut;
-
-        {
-            JSONObject jsonRoot(jsonOut);
-            jsonRoot.attr("version", 1);
-
-            {
-                auto res = jsonRoot.placeholder("root");
-                listNar(res, ref<FSAccessor>(narAccessor), "", true);
-            }
-        }
+        nlohmann::json j = {
+            {"version", 1},
+            {"root", listNar(ref<FSAccessor>(narAccessor), "", true)},
+        };
 
-        upsertFile(std::string(info.path.hashPart()) + ".ls", jsonOut.str(), "application/json");
+        upsertFile(std::string(info.path.hashPart()) + ".ls", j.dump(), "application/json");
     }
 
     /* Optionally maintain an index of DWARF debug info files
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 00e375fe9..1938f4bcb 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -7,7 +7,6 @@
 #include "finally.hh"
 #include "util.hh"
 #include "archive.hh"
-#include "json.hh"
 #include "compression.hh"
 #include "worker-protocol.hh"
 #include "topo-sort.hh"
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 3439dd2cc..ef49f8bf1 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -8,7 +8,6 @@
 #include "finally.hh"
 #include "util.hh"
 #include "archive.hh"
-#include "json.hh"
 #include "compression.hh"
 #include "daemon.hh"
 #include "worker-protocol.hh"
@@ -56,6 +55,7 @@
 
 #include <pwd.h>
 #include <grp.h>
+#include <iostream>
 
 namespace nix {
 
diff --git a/src/libstore/nar-accessor.cc b/src/libstore/nar-accessor.cc
index 398147fc3..9a0003588 100644
--- a/src/libstore/nar-accessor.cc
+++ b/src/libstore/nar-accessor.cc
@@ -1,6 +1,5 @@
 #include "nar-accessor.hh"
 #include "archive.hh"
-#include "json.hh"
 
 #include <map>
 #include <stack>
@@ -243,42 +242,43 @@ ref<FSAccessor> makeLazyNarAccessor(const std::string & listing,
     return make_ref<NarAccessor>(listing, getNarBytes);
 }
 
-void listNar(JSONPlaceholder & res, ref<FSAccessor> accessor,
-    const Path & path, bool recurse)
+using nlohmann::json;
+json listNar(ref<FSAccessor> accessor, const Path & path, bool recurse)
 {
     auto st = accessor->stat(path);
 
-    auto obj = res.object();
+    json obj = json::object();
 
     switch (st.type) {
     case FSAccessor::Type::tRegular:
-        obj.attr("type", "regular");
-        obj.attr("size", st.fileSize);
+        obj["type"] = "regular";
+        obj["size"] = st.fileSize;
         if (st.isExecutable)
-            obj.attr("executable", true);
+            obj["executable"] = true;
         if (st.narOffset)
-            obj.attr("narOffset", st.narOffset);
+            obj["narOffset"] = st.narOffset;
         break;
     case FSAccessor::Type::tDirectory:
-        obj.attr("type", "directory");
+        obj["type"] = "directory";
         {
-            auto res2 = obj.object("entries");
+            obj["entries"] = json::object();
+            json &res2 = obj["entries"];
             for (auto & name : accessor->readDirectory(path)) {
                 if (recurse) {
-                    auto res3 = res2.placeholder(name);
-                    listNar(res3, accessor, path + "/" + name, true);
+                    res2[name] = listNar(accessor, path + "/" + name, true);
                 } else
-                    res2.object(name);
+                    res2[name] = json::object();
             }
         }
         break;
     case FSAccessor::Type::tSymlink:
-        obj.attr("type", "symlink");
-        obj.attr("target", accessor->readLink(path));
+        obj["type"] = "symlink";
+        obj["target"] = accessor->readLink(path);
         break;
     default:
         throw Error("path '%s' does not exist in NAR", path);
     }
+    return obj;
 }
 
 }
diff --git a/src/libstore/nar-accessor.hh b/src/libstore/nar-accessor.hh
index c2241a04c..7d998ae0b 100644
--- a/src/libstore/nar-accessor.hh
+++ b/src/libstore/nar-accessor.hh
@@ -2,6 +2,7 @@
 
 #include <functional>
 
+#include <nlohmann/json_fwd.hpp>
 #include "fs-accessor.hh"
 
 namespace nix {
@@ -24,11 +25,8 @@ ref<FSAccessor> makeLazyNarAccessor(
     const std::string & listing,
     GetNarBytes getNarBytes);
 
-class JSONPlaceholder;
-
 /* Write a JSON representation of the contents of a NAR (except file
    contents). */
-void listNar(JSONPlaceholder & res, ref<FSAccessor> accessor,
-    const Path & path, bool recurse);
+nlohmann::json listNar(ref<FSAccessor> accessor, const Path & path, bool recurse);
 
 }
diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index f2288a04e..59a30db10 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -2,7 +2,6 @@
 
 #include <nlohmann/json.hpp>
 #include <regex>
-#include "json.hh"
 
 namespace nix {
 
@@ -144,16 +143,11 @@ std::optional<nlohmann::json> ParsedDerivation::prepareStructuredAttrs(Store & s
     auto e = json.find("exportReferencesGraph");
     if (e != json.end() && e->is_object()) {
         for (auto i = e->begin(); i != e->end(); ++i) {
-            std::ostringstream str;
-            {
-                JSONPlaceholder jsonRoot(str, true);
-                StorePathSet storePaths;
-                for (auto & p : *i)
-                    storePaths.insert(store.parseStorePath(p.get<std::string>()));
-                store.pathInfoToJSON(jsonRoot,
-                    store.exportReferences(storePaths, inputPaths), false, true);
-            }
-            json[i.key()] = nlohmann::json::parse(str.str()); // urgh
+            StorePathSet storePaths;
+            for (auto & p : *i)
+                storePaths.insert(store.parseStorePath(p.get<std::string>()));
+            json[i.key()] = store.pathInfoToJSON(
+                store.exportReferences(storePaths, inputPaths), false, true);
         }
     }
 
diff --git a/src/libstore/remote-fs-accessor.cc b/src/libstore/remote-fs-accessor.cc
index 0ce335646..fcfb527f5 100644
--- a/src/libstore/remote-fs-accessor.cc
+++ b/src/libstore/remote-fs-accessor.cc
@@ -1,6 +1,6 @@
+#include <nlohmann/json.hpp>
 #include "remote-fs-accessor.hh"
 #include "nar-accessor.hh"
-#include "json.hh"
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -38,10 +38,8 @@ ref<FSAccessor> RemoteFSAccessor::addToCache(std::string_view hashPart, std::str
 
     if (cacheDir != "") {
         try {
-            std::ostringstream str;
-            JSONPlaceholder jsonRoot(str);
-            listNar(jsonRoot, narAccessor, "", true);
-            writeFile(makeCacheFile(hashPart, "ls"), str.str());
+            nlohmann::json j = listNar(narAccessor, "", true);
+            writeFile(makeCacheFile(hashPart, "ls"), j.dump());
         } catch (...) {
             ignoreException();
         }
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 06a9758fc..8811ab578 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -6,14 +6,16 @@
 #include "util.hh"
 #include "nar-info-disk-cache.hh"
 #include "thread-pool.hh"
-#include "json.hh"
 #include "url.hh"
 #include "archive.hh"
 #include "callback.hh"
 #include "remote-store.hh"
 
+#include <nlohmann/json.hpp>
 #include <regex>
 
+using json = nlohmann::json;
+
 namespace nix {
 
 
@@ -838,56 +840,53 @@ StorePathSet Store::exportReferences(const StorePathSet & storePaths, const Stor
     return paths;
 }
 
-
-void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const StorePathSet & storePaths,
+json Store::pathInfoToJSON(const StorePathSet & storePaths,
     bool includeImpureInfo, bool showClosureSize,
     Base hashBase,
     AllowInvalidFlag allowInvalid)
 {
-    auto jsonList = jsonOut.list();
+    json::array_t jsonList = json::array();
 
     for (auto & storePath : storePaths) {
-        auto jsonPath = jsonList.object();
+        auto& jsonPath = jsonList.emplace_back(json::object());
 
         try {
             auto info = queryPathInfo(storePath);
 
-            jsonPath.attr("path", printStorePath(info->path));
-            jsonPath
-                .attr("narHash", info->narHash.to_string(hashBase, true))
-                .attr("narSize", info->narSize);
+            jsonPath["path"] = printStorePath(info->path);
+            jsonPath["narHash"] = info->narHash.to_string(hashBase, true);
+            jsonPath["narSize"] = info->narSize;
 
             {
-                auto jsonRefs = jsonPath.list("references");
+                auto& jsonRefs = (jsonPath["references"] = json::array());
                 for (auto & ref : info->references)
-                    jsonRefs.elem(printStorePath(ref));
+                    jsonRefs.emplace_back(printStorePath(ref));
             }
 
             if (info->ca)
-                jsonPath.attr("ca", renderContentAddress(info->ca));
+                jsonPath["ca"] = renderContentAddress(info->ca);
 
             std::pair<uint64_t, uint64_t> closureSizes;
 
             if (showClosureSize) {
                 closureSizes = getClosureSize(info->path);
-                jsonPath.attr("closureSize", closureSizes.first);
+                jsonPath["closureSize"] = closureSizes.first;
             }
 
             if (includeImpureInfo) {
 
                 if (info->deriver)
-                    jsonPath.attr("deriver", printStorePath(*info->deriver));
+                    jsonPath["deriver"] = printStorePath(*info->deriver);
 
                 if (info->registrationTime)
-                    jsonPath.attr("registrationTime", info->registrationTime);
+                    jsonPath["registrationTime"] = info->registrationTime;
 
                 if (info->ultimate)
-                    jsonPath.attr("ultimate", info->ultimate);
+                    jsonPath["ultimate"] = info->ultimate;
 
                 if (!info->sigs.empty()) {
-                    auto jsonSigs = jsonPath.list("signatures");
                     for (auto & sig : info->sigs)
-                        jsonSigs.elem(sig);
+                        jsonPath["signatures"].push_back(sig);
                 }
 
                 auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
@@ -895,21 +894,22 @@ void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const StorePathSet & store
 
                 if (narInfo) {
                     if (!narInfo->url.empty())
-                        jsonPath.attr("url", narInfo->url);
+                        jsonPath["url"] = narInfo->url;
                     if (narInfo->fileHash)
-                        jsonPath.attr("downloadHash", narInfo->fileHash->to_string(hashBase, true));
+                        jsonPath["downloadHash"] = narInfo->fileHash->to_string(hashBase, true);
                     if (narInfo->fileSize)
-                        jsonPath.attr("downloadSize", narInfo->fileSize);
+                        jsonPath["downloadSize"] = narInfo->fileSize;
                     if (showClosureSize)
-                        jsonPath.attr("closureDownloadSize", closureSizes.second);
+                        jsonPath["closureDownloadSize"] = closureSizes.second;
                 }
             }
 
         } catch (InvalidPath &) {
-            jsonPath.attr("path", printStorePath(storePath));
-            jsonPath.attr("valid", false);
+            jsonPath["path"] = printStorePath(storePath);
+            jsonPath["valid"] = false;
         }
     }
+    return jsonList;
 }
 
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index c8a667c6d..151ec10d6 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -14,6 +14,7 @@
 #include "path-info.hh"
 #include "repair-flag.hh"
 
+#include <nlohmann/json_fwd.hpp>
 #include <atomic>
 #include <limits>
 #include <map>
@@ -68,7 +69,6 @@ struct Derivation;
 class FSAccessor;
 class NarInfoDiskCache;
 class Store;
-class JSONPlaceholder;
 
 
 enum CheckSigsFlag : bool { NoCheckSigs = false, CheckSigs = true };
@@ -512,7 +512,7 @@ public:
        variable elements such as the registration time are
        included. If ‘showClosureSize’ is true, the closure size of
        each path is included. */
-    void pathInfoToJSON(JSONPlaceholder & jsonOut, const StorePathSet & storePaths,
+    nlohmann::json pathInfoToJSON(const StorePathSet & storePaths,
         bool includeImpureInfo, bool showClosureSize,
         Base hashBase = Base32,
         AllowInvalidFlag allowInvalid = DisallowInvalid);
diff --git a/src/libutil/json.cc b/src/libutil/json.cc
deleted file mode 100644
index 2f9e97ff5..000000000
--- a/src/libutil/json.cc
+++ /dev/null
@@ -1,203 +0,0 @@
-#include "json.hh"
-
-#include <iomanip>
-#include <cstdint>
-#include <cstring>
-
-namespace nix {
-
-template<>
-void toJSON<std::string_view>(std::ostream & str, const std::string_view & s)
-{
-    constexpr size_t BUF_SIZE = 4096;
-    char buf[BUF_SIZE + 7]; // BUF_SIZE + largest single sequence of puts
-    size_t bufPos = 0;
-
-    const auto flush = [&] {
-        str.write(buf, bufPos);
-        bufPos = 0;
-    };
-    const auto put = [&] (char c) {
-        buf[bufPos++] = c;
-    };
-
-    put('"');
-    for (auto i = s.begin(); i != s.end(); i++) {
-        if (bufPos >= BUF_SIZE) flush();
-        if (*i == '\"' || *i == '\\') { put('\\'); put(*i); }
-        else if (*i == '\n') { put('\\'); put('n'); }
-        else if (*i == '\r') { put('\\'); put('r'); }
-        else if (*i == '\t') { put('\\'); put('t'); }
-        else if (*i >= 0 && *i < 32) {
-            const char hex[17] = "0123456789abcdef";
-            put('\\');
-            put('u');
-            put(hex[(uint16_t(*i) >> 12) & 0xf]);
-            put(hex[(uint16_t(*i) >>  8) & 0xf]);
-            put(hex[(uint16_t(*i) >>  4) & 0xf]);
-            put(hex[(uint16_t(*i) >>  0) & 0xf]);
-        }
-        else put(*i);
-    }
-    put('"');
-    flush();
-}
-
-void toJSON(std::ostream & str, const char * s)
-{
-    if (!s) str << "null"; else toJSON(str, std::string_view(s));
-}
-
-template<> void toJSON<int>(std::ostream & str, const int & n) { str << n; }
-template<> void toJSON<unsigned int>(std::ostream & str, const unsigned int & n) { str << n; }
-template<> void toJSON<long>(std::ostream & str, const long & n) { str << n; }
-template<> void toJSON<unsigned long>(std::ostream & str, const unsigned long & n) { str << n; }
-template<> void toJSON<long long>(std::ostream & str, const long long & n) { str << n; }
-template<> void toJSON<unsigned long long>(std::ostream & str, const unsigned long long & n) { str << n; }
-template<> void toJSON<float>(std::ostream & str, const float & n) { str << n; }
-template<> void toJSON<double>(std::ostream & str, const double & n) { str << n; }
-template<> void toJSON<std::string>(std::ostream & str, const std::string & s) { toJSON(str, (std::string_view) s); }
-
-template<> void toJSON<bool>(std::ostream & str, const bool & b)
-{
-    str << (b ? "true" : "false");
-}
-
-template<> void toJSON<std::nullptr_t>(std::ostream & str, const std::nullptr_t & b)
-{
-    str << "null";
-}
-
-JSONWriter::JSONWriter(std::ostream & str, bool indent)
-    : state(new JSONState(str, indent))
-{
-    state->stack++;
-}
-
-JSONWriter::JSONWriter(JSONState * state)
-    : state(state)
-{
-    state->stack++;
-}
-
-JSONWriter::~JSONWriter()
-{
-    if (state) {
-        assertActive();
-        state->stack--;
-        if (state->stack == 0) delete state;
-    }
-}
-
-void JSONWriter::comma()
-{
-    assertActive();
-    if (first) {
-        first = false;
-    } else {
-        state->str << ',';
-    }
-    if (state->indent) indent();
-}
-
-void JSONWriter::indent()
-{
-    state->str << '\n' << std::string(state->depth * 2, ' ');
-}
-
-void JSONList::open()
-{
-    state->depth++;
-    state->str << '[';
-}
-
-JSONList::~JSONList()
-{
-    state->depth--;
-    if (state->indent && !first) indent();
-    state->str << "]";
-}
-
-JSONList JSONList::list()
-{
-    comma();
-    return JSONList(state);
-}
-
-JSONObject JSONList::object()
-{
-    comma();
-    return JSONObject(state);
-}
-
-JSONPlaceholder JSONList::placeholder()
-{
-    comma();
-    return JSONPlaceholder(state);
-}
-
-void JSONObject::open()
-{
-    state->depth++;
-    state->str << '{';
-}
-
-JSONObject::~JSONObject()
-{
-    if (state) {
-        state->depth--;
-        if (state->indent && !first) indent();
-        state->str << "}";
-    }
-}
-
-void JSONObject::attr(std::string_view s)
-{
-    comma();
-    toJSON(state->str, s);
-    state->str << ':';
-    if (state->indent) state->str << ' ';
-}
-
-JSONList JSONObject::list(std::string_view name)
-{
-    attr(name);
-    return JSONList(state);
-}
-
-JSONObject JSONObject::object(std::string_view name)
-{
-    attr(name);
-    return JSONObject(state);
-}
-
-JSONPlaceholder JSONObject::placeholder(std::string_view name)
-{
-    attr(name);
-    return JSONPlaceholder(state);
-}
-
-JSONList JSONPlaceholder::list()
-{
-    assertValid();
-    first = false;
-    return JSONList(state);
-}
-
-JSONObject JSONPlaceholder::object()
-{
-    assertValid();
-    first = false;
-    return JSONObject(state);
-}
-
-JSONPlaceholder::~JSONPlaceholder()
-{
-    if (first) {
-        assert(std::uncaught_exceptions());
-        if (state->stack != 0)
-            write(nullptr);
-    }
-}
-
-}
diff --git a/src/libutil/json.hh b/src/libutil/json.hh
deleted file mode 100644
index 3790b1a2e..000000000
--- a/src/libutil/json.hh
+++ /dev/null
@@ -1,185 +0,0 @@
-#pragma once
-
-#include <iostream>
-#include <vector>
-#include <cassert>
-
-namespace nix {
-
-void toJSON(std::ostream & str, const char * s);
-
-template<typename T>
-void toJSON(std::ostream & str, const T & n);
-
-class JSONWriter
-{
-protected:
-
-    struct JSONState
-    {
-        std::ostream & str;
-        bool indent;
-        size_t depth = 0;
-        size_t stack = 0;
-        JSONState(std::ostream & str, bool indent) : str(str), indent(indent) { }
-        ~JSONState()
-        {
-            assert(stack == 0);
-        }
-    };
-
-    JSONState * state;
-
-    bool first = true;
-
-    JSONWriter(std::ostream & str, bool indent);
-
-    JSONWriter(JSONState * state);
-
-    ~JSONWriter();
-
-    void assertActive()
-    {
-        assert(state->stack != 0);
-    }
-
-    void comma();
-
-    void indent();
-};
-
-class JSONObject;
-class JSONPlaceholder;
-
-class JSONList : JSONWriter
-{
-private:
-
-    friend class JSONObject;
-    friend class JSONPlaceholder;
-
-    void open();
-
-    JSONList(JSONState * state)
-        : JSONWriter(state)
-    {
-        open();
-    }
-
-public:
-
-    JSONList(std::ostream & str, bool indent = false)
-        : JSONWriter(str, indent)
-    {
-        open();
-    }
-
-    ~JSONList();
-
-    template<typename T>
-    JSONList & elem(const T & v)
-    {
-        comma();
-        toJSON(state->str, v);
-        return *this;
-    }
-
-    JSONList list();
-
-    JSONObject object();
-
-    JSONPlaceholder placeholder();
-};
-
-class JSONObject : JSONWriter
-{
-private:
-
-    friend class JSONList;
-    friend class JSONPlaceholder;
-
-    void open();
-
-    JSONObject(JSONState * state)
-        : JSONWriter(state)
-    {
-        open();
-    }
-
-    void attr(std::string_view s);
-
-public:
-
-    JSONObject(std::ostream & str, bool indent = false)
-        : JSONWriter(str, indent)
-    {
-        open();
-    }
-
-    JSONObject(const JSONObject & obj) = delete;
-
-    JSONObject(JSONObject && obj)
-        : JSONWriter(obj.state)
-    {
-        obj.state = 0;
-    }
-
-    ~JSONObject();
-
-    template<typename T>
-    JSONObject & attr(std::string_view name, const T & v)
-    {
-        attr(name);
-        toJSON(state->str, v);
-        return *this;
-    }
-
-    JSONList list(std::string_view name);
-
-    JSONObject object(std::string_view name);
-
-    JSONPlaceholder placeholder(std::string_view name);
-};
-
-class JSONPlaceholder : JSONWriter
-{
-
-private:
-
-    friend class JSONList;
-    friend class JSONObject;
-
-    JSONPlaceholder(JSONState * state)
-        : JSONWriter(state)
-    {
-    }
-
-    void assertValid()
-    {
-        assertActive();
-        assert(first);
-    }
-
-public:
-
-    JSONPlaceholder(std::ostream & str, bool indent = false)
-        : JSONWriter(str, indent)
-    {
-    }
-
-    ~JSONPlaceholder();
-
-    template<typename T>
-    void write(const T & v)
-    {
-        assertValid();
-        first = false;
-        toJSON(state->str, v);
-    }
-
-    JSONList list();
-
-    JSONObject object();
-};
-
-}
diff --git a/src/libutil/tests/json.cc b/src/libutil/tests/json.cc
deleted file mode 100644
index 156286999..000000000
--- a/src/libutil/tests/json.cc
+++ /dev/null
@@ -1,193 +0,0 @@
-#include "json.hh"
-#include <gtest/gtest.h>
-#include <sstream>
-
-namespace nix {
-
-    /* ----------------------------------------------------------------------------
-     * toJSON
-     * --------------------------------------------------------------------------*/
-
-    TEST(toJSON, quotesCharPtr) {
-        const char* input = "test";
-        std::stringstream out;
-        toJSON(out, input);
-
-        ASSERT_EQ(out.str(), "\"test\"");
-    }
-
-    TEST(toJSON, quotesStdString) {
-        std::string input = "test";
-        std::stringstream out;
-        toJSON(out, input);
-
-        ASSERT_EQ(out.str(), "\"test\"");
-    }
-
-    TEST(toJSON, convertsNullptrtoNull) {
-        auto input = nullptr;
-        std::stringstream out;
-        toJSON(out, input);
-
-        ASSERT_EQ(out.str(), "null");
-    }
-
-    TEST(toJSON, convertsNullToNull) {
-        const char* input = 0;
-        std::stringstream out;
-        toJSON(out, input);
-
-        ASSERT_EQ(out.str(), "null");
-    }
-
-
-    TEST(toJSON, convertsFloat) {
-        auto input = 1.024f;
-        std::stringstream out;
-        toJSON(out, input);
-
-        ASSERT_EQ(out.str(), "1.024");
-    }
-
-    TEST(toJSON, convertsDouble) {
-        const double input = 1.024;
-        std::stringstream out;
-        toJSON(out, input);
-
-        ASSERT_EQ(out.str(), "1.024");
-    }
-
-    TEST(toJSON, convertsBool) {
-        auto input = false;
-        std::stringstream out;
-        toJSON(out, input);
-
-        ASSERT_EQ(out.str(), "false");
-    }
-
-    TEST(toJSON, quotesTab) {
-        std::stringstream out;
-        toJSON(out, "\t");
-
-        ASSERT_EQ(out.str(), "\"\\t\"");
-    }
-
-    TEST(toJSON, quotesNewline) {
-        std::stringstream out;
-        toJSON(out, "\n");
-
-        ASSERT_EQ(out.str(), "\"\\n\"");
-    }
-
-    TEST(toJSON, quotesCreturn) {
-        std::stringstream out;
-        toJSON(out, "\r");
-
-        ASSERT_EQ(out.str(), "\"\\r\"");
-    }
-
-    TEST(toJSON, quotesCreturnNewLine) {
-        std::stringstream out;
-        toJSON(out, "\r\n");
-
-        ASSERT_EQ(out.str(), "\"\\r\\n\"");
-    }
-
-    TEST(toJSON, quotesDoublequotes) {
-        std::stringstream out;
-        toJSON(out, "\"");
-
-        ASSERT_EQ(out.str(), "\"\\\"\"");
-    }
-
-    TEST(toJSON, substringEscape) {
-        std::stringstream out;
-        std::string_view s = "foo\t";
-        toJSON(out, s.substr(3));
-
-        ASSERT_EQ(out.str(), "\"\\t\"");
-    }
-
-    /* ----------------------------------------------------------------------------
-     * JSONObject
-     * --------------------------------------------------------------------------*/
-
-    TEST(JSONObject, emptyObject) {
-        std::stringstream out;
-        {
-            JSONObject t(out);
-        }
-        ASSERT_EQ(out.str(), "{}");
-    }
-
-    TEST(JSONObject, objectWithList) {
-        std::stringstream out;
-        {
-            JSONObject t(out);
-            auto l = t.list("list");
-            l.elem("element");
-        }
-        ASSERT_EQ(out.str(), R"#({"list":["element"]})#");
-    }
-
-    TEST(JSONObject, objectWithListIndent) {
-        std::stringstream out;
-        {
-            JSONObject t(out, true);
-            auto l = t.list("list");
-            l.elem("element");
-        }
-        ASSERT_EQ(out.str(),
-R"#({
-  "list": [
-    "element"
-  ]
-})#");
-    }
-
-    TEST(JSONObject, objectWithPlaceholderAndList) {
-        std::stringstream out;
-        {
-            JSONObject t(out);
-            auto l = t.placeholder("list");
-            l.list().elem("element");
-        }
-
-        ASSERT_EQ(out.str(), R"#({"list":["element"]})#");
-    }
-
-    TEST(JSONObject, objectWithPlaceholderAndObject) {
-        std::stringstream out;
-        {
-            JSONObject t(out);
-            auto l = t.placeholder("object");
-            l.object().attr("key", "value");
-        }
-
-        ASSERT_EQ(out.str(), R"#({"object":{"key":"value"}})#");
-    }
-
-    /* ----------------------------------------------------------------------------
-     * JSONList
-     * --------------------------------------------------------------------------*/
-
-    TEST(JSONList, empty) {
-        std::stringstream out;
-        {
-            JSONList l(out);
-        }
-        ASSERT_EQ(out.str(), R"#([])#");
-    }
-
-    TEST(JSONList, withElements) {
-        std::stringstream out;
-        {
-            JSONList l(out);
-            l.elem("one");
-            l.object();
-            l.placeholder().write("three");
-        }
-        ASSERT_EQ(out.str(), R"#(["one",{},"three"])#");
-    }
-}
-
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index fdd66220a..776c5f6db 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -12,7 +12,6 @@
 #include "local-fs-store.hh"
 #include "user-env.hh"
 #include "util.hh"
-#include "json.hh"
 #include "value-to-json.hh"
 #include "xml-writer.hh"
 #include "legacy.hh"
@@ -26,6 +25,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include <nlohmann/json.hpp>
 
 using namespace nix;
 using std::cout;
@@ -911,43 +911,47 @@ static VersionDiff compareVersionAgainstSet(
 
 static void queryJSON(Globals & globals, std::vector<DrvInfo> & elems, bool printOutPath, bool printMeta)
 {
-    JSONObject topObj(cout, true);
+    using nlohmann::json;
+    json topObj = json::object();
     for (auto & i : elems) {
         try {
             if (i.hasFailed()) continue;
 
-            JSONObject pkgObj = topObj.object(i.attrPath);
 
             auto drvName = DrvName(i.queryName());
-            pkgObj.attr("name", drvName.fullName);
-            pkgObj.attr("pname", drvName.name);
-            pkgObj.attr("version", drvName.version);
-            pkgObj.attr("system", i.querySystem());
-            pkgObj.attr("outputName", i.queryOutputName());
+            json &pkgObj = topObj[i.attrPath];
+            pkgObj = {
+                {"name", drvName.fullName},
+                {"pname", drvName.name},
+                {"version", drvName.version},
+                {"system", i.querySystem()},
+                {"outputName", i.queryOutputName()},
+            };
 
             {
                 DrvInfo::Outputs outputs = i.queryOutputs(printOutPath);
-                JSONObject outputObj = pkgObj.object("outputs");
+                json &outputObj = pkgObj["outputs"];
+                outputObj = json::object();
                 for (auto & j : outputs) {
                     if (j.second)
-                        outputObj.attr(j.first, globals.state->store->printStorePath(*j.second));
+                        outputObj[j.first] = globals.state->store->printStorePath(*j.second);
                     else
-                        outputObj.attr(j.first, nullptr);
+                        outputObj[j.first] = nullptr;
                 }
             }
 
             if (printMeta) {
-                JSONObject metaObj = pkgObj.object("meta");
+                json &metaObj = pkgObj["meta"];
+                metaObj = json::object();
                 StringSet metaNames = i.queryMetaNames();
                 for (auto & j : metaNames) {
                     Value * v = i.queryMeta(j);
                     if (!v) {
                         printError("derivation '%s' has invalid meta attribute '%s'", i.queryName(), j);
-                        metaObj.attr(j, nullptr);
+                        metaObj[j] = nullptr;
                     } else {
-                        auto placeholder = metaObj.placeholder(j);
                         PathSet context;
-                        printValueAsJSON(*globals.state, true, *v, noPos, placeholder, context);
+                        metaObj[j] = printValueAsJSON(*globals.state, true, *v, noPos, context);
                     }
                 }
             }
@@ -958,6 +962,7 @@ static void queryJSON(Globals & globals, std::vector<DrvInfo> & elems, bool prin
             throw;
         }
     }
+    std::cout << topObj.dump(2);
 }
 
 
diff --git a/src/nix/eval.cc b/src/nix/eval.cc
index ddd2790c6..ba82b5772 100644
--- a/src/nix/eval.cc
+++ b/src/nix/eval.cc
@@ -4,10 +4,11 @@
 #include "store-api.hh"
 #include "eval.hh"
 #include "eval-inline.hh"
-#include "json.hh"
 #include "value-to-json.hh"
 #include "progress-bar.hh"
 
+#include <nlohmann/json.hpp>
+
 using namespace nix;
 
 struct CmdEval : MixJSON, InstallableCommand
@@ -115,9 +116,7 @@ struct CmdEval : MixJSON, InstallableCommand
         }
 
         else if (json) {
-            JSONPlaceholder jsonOut(std::cout);
-            printValueAsJSON(*state, true, *v, pos, jsonOut, context, false);
-            std::cout << std::endl;
+            std::cout << printValueAsJSON(*state, true, *v, pos, context, false).dump() << std::endl;
         }
 
         else {
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 3967f1102..336f6723a 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -11,7 +11,6 @@
 #include "attr-path.hh"
 #include "fetchers.hh"
 #include "registry.hh"
-#include "json.hh"
 #include "eval-cache.hh"
 #include "markdown.hh"
 
@@ -21,6 +20,7 @@
 
 using namespace nix;
 using namespace nix::flake;
+using json = nlohmann::json;
 
 class FlakeCommand : virtual Args, public MixFlakeOptions
 {
@@ -917,35 +917,44 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
     {
         auto flake = lockFlake();
 
-        auto jsonRoot = json ? std::optional<JSONObject>(std::cout) : std::nullopt;
-
         StorePathSet sources;
 
         sources.insert(flake.flake.sourceInfo->storePath);
-        if (jsonRoot)
-            jsonRoot->attr("path", store->printStorePath(flake.flake.sourceInfo->storePath));
 
         // FIXME: use graph output, handle cycles.
-        std::function<void(const Node & node, std::optional<JSONObject> & jsonObj)> traverse;
-        traverse = [&](const Node & node, std::optional<JSONObject> & jsonObj)
+        std::function<nlohmann::json(const Node & node)> traverse;
+        traverse = [&](const Node & node)
         {
-            auto jsonObj2 = jsonObj ? jsonObj->object("inputs") : std::optional<JSONObject>();
+            nlohmann::json jsonObj2 = json ? json::object() : nlohmann::json(nullptr);
             for (auto & [inputName, input] : node.inputs) {
                 if (auto inputNode = std::get_if<0>(&input)) {
-                    auto jsonObj3 = jsonObj2 ? jsonObj2->object(inputName) : std::optional<JSONObject>();
                     auto storePath =
                         dryRun
                         ? (*inputNode)->lockedRef.input.computeStorePath(*store)
                         : (*inputNode)->lockedRef.input.fetch(store).first.storePath;
-                    if (jsonObj3)
-                        jsonObj3->attr("path", store->printStorePath(storePath));
-                    sources.insert(std::move(storePath));
-                    traverse(**inputNode, jsonObj3);
+                    if (json) {
+                        auto& jsonObj3 = jsonObj2[inputName];
+                        jsonObj3["path"] = store->printStorePath(storePath);
+                        sources.insert(std::move(storePath));
+                        jsonObj3["inputs"] = traverse(**inputNode);
+                    } else {
+                        sources.insert(std::move(storePath));
+                        traverse(**inputNode);
+                    }
                 }
             }
+            return jsonObj2;
         };
 
-        traverse(*flake.lockFile.root, jsonRoot);
+        if (json) {
+            nlohmann::json jsonRoot = {
+                {"path", store->printStorePath(flake.flake.sourceInfo->storePath)},
+                {"inputs", traverse(*flake.lockFile.root)},
+            };
+            std::cout << jsonRoot.dump() << std::endl;
+        } else {
+            traverse(*flake.lockFile.root);
+        }
 
         if (!dryRun && !dstUri.empty()) {
             ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index 07554994b..e964b01b3 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -3,7 +3,7 @@
 #include "fs-accessor.hh"
 #include "nar-accessor.hh"
 #include "common-args.hh"
-#include "json.hh"
+#include <nlohmann/json.hpp>
 
 using namespace nix;
 
@@ -91,10 +91,9 @@ struct MixLs : virtual Args, MixJSON
         if (path == "/") path = "";
 
         if (json) {
-            JSONPlaceholder jsonRoot(std::cout);
             if (showDirectory)
                 throw UsageError("'--directory' is useless with '--json'");
-            listNar(jsonRoot, accessor, path, recursive);
+            std::cout << listNar(accessor, path, recursive);
         } else
             listText(accessor);
     }
diff --git a/src/nix/make-content-addressed.cc b/src/nix/make-content-addressed.cc
index 34860c38f..f2e4cefbe 100644
--- a/src/nix/make-content-addressed.cc
+++ b/src/nix/make-content-addressed.cc
@@ -2,10 +2,13 @@
 #include "store-api.hh"
 #include "make-content-addressed.hh"
 #include "common-args.hh"
-#include "json.hh"
+
+#include <nlohmann/json.hpp>
 
 using namespace nix;
 
+using nlohmann::json;
+
 struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand, MixJSON
 {
     CmdMakeContentAddressed()
@@ -25,6 +28,7 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
           ;
     }
 
+    using StorePathsCommand::run;
     void run(ref<Store> srcStore, StorePaths && storePaths) override
     {
         auto dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
@@ -33,13 +37,13 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
             StorePathSet(storePaths.begin(), storePaths.end()));
 
         if (json) {
-            JSONObject jsonRoot(std::cout);
-            JSONObject jsonRewrites(jsonRoot.object("rewrites"));
+            nlohmann::json jsonRewrites = json::object();
             for (auto & path : storePaths) {
                 auto i = remappings.find(path);
                 assert(i != remappings.end());
-                jsonRewrites.attr(srcStore->printStorePath(path), srcStore->printStorePath(i->second));
+                jsonRewrites[srcStore->printStorePath(path)] = srcStore->printStorePath(i->second);
             }
+            std::cout << json::object({"rewrites", jsonRewrites}).dump();
         } else {
             for (auto & path : storePaths) {
                 auto i = remappings.find(path);
diff --git a/src/nix/path-info.cc b/src/nix/path-info.cc
index d690fe594..613c5b191 100644
--- a/src/nix/path-info.cc
+++ b/src/nix/path-info.cc
@@ -1,12 +1,13 @@
 #include "command.hh"
 #include "shared.hh"
 #include "store-api.hh"
-#include "json.hh"
 #include "common-args.hh"
 
 #include <algorithm>
 #include <array>
 
+#include <nlohmann/json.hpp>
+
 using namespace nix;
 
 struct CmdPathInfo : StorePathsCommand, MixJSON
@@ -86,11 +87,10 @@ struct CmdPathInfo : StorePathsCommand, MixJSON
             pathLen = std::max(pathLen, store->printStorePath(storePath).size());
 
         if (json) {
-            JSONPlaceholder jsonRoot(std::cout);
-            store->pathInfoToJSON(jsonRoot,
+            std::cout << store->pathInfoToJSON(
                 // FIXME: preserve order?
                 StorePathSet(storePaths.begin(), storePaths.end()),
-                true, showClosureSize, SRI, AllowInvalid);
+                true, showClosureSize, SRI, AllowInvalid).dump();
         }
 
         else {
diff --git a/src/nix/search.cc b/src/nix/search.cc
index bdd45cbed..d2a31607d 100644
--- a/src/nix/search.cc
+++ b/src/nix/search.cc
@@ -5,7 +5,6 @@
 #include "names.hh"
 #include "get-drvs.hh"
 #include "common-args.hh"
-#include "json.hh"
 #include "shared.hh"
 #include "eval-cache.hh"
 #include "attr-path.hh"
@@ -13,8 +12,10 @@
 
 #include <regex>
 #include <fstream>
+#include <nlohmann/json.hpp>
 
 using namespace nix;
+using json = nlohmann::json;
 
 std::string wrap(std::string prefix, std::string s)
 {
@@ -84,7 +85,8 @@ struct CmdSearch : InstallableCommand, MixJSON
 
         auto state = getEvalState();
 
-        auto jsonOut = json ? std::make_unique<JSONObject>(std::cout) : nullptr;
+        std::optional<nlohmann::json> jsonOut;
+        if (json) jsonOut = json::object();
 
         uint64_t results = 0;
 
@@ -151,10 +153,11 @@ struct CmdSearch : InstallableCommand, MixJSON
                     {
                         results++;
                         if (json) {
-                            auto jsonElem = jsonOut->object(attrPath2);
-                            jsonElem.attr("pname", name.name);
-                            jsonElem.attr("version", name.version);
-                            jsonElem.attr("description", description);
+                            (*jsonOut)[attrPath2] = {
+                                {"pname", name.name},
+                                {"version", name.version},
+                                {"description", description},
+                            };
                         } else {
                             auto name2 = hiliteMatches(name.name, nameMatches, ANSI_GREEN, "\e[0;2m");
                             if (results > 1) logger->cout("");
@@ -193,6 +196,10 @@ struct CmdSearch : InstallableCommand, MixJSON
         for (auto & cursor : installable->getCursors(*state))
             visit(*cursor, cursor->getAttrPath(), true);
 
+        if (json) {
+            std::cout << jsonOut->dump() << std::endl;
+        }
+
         if (!json && !results)
             throw Error("no results for the given search term(s)!");
     }
diff --git a/src/nix/show-derivation.cc b/src/nix/show-derivation.cc
index fb46b4dbf..af2e676a4 100644
--- a/src/nix/show-derivation.cc
+++ b/src/nix/show-derivation.cc
@@ -5,10 +5,11 @@
 #include "common-args.hh"
 #include "store-api.hh"
 #include "archive.hh"
-#include "json.hh"
 #include "derivations.hh"
+#include <nlohmann/json.hpp>
 
 using namespace nix;
+using json = nlohmann::json;
 
 struct CmdShowDerivation : InstallablesCommand
 {
@@ -48,77 +49,63 @@ struct CmdShowDerivation : InstallablesCommand
             drvPaths = std::move(closure);
         }
 
-        {
-
-        JSONObject jsonRoot(std::cout, true);
+        json jsonRoot = json::object();
 
         for (auto & drvPath : drvPaths) {
             if (!drvPath.isDerivation()) continue;
 
-            auto drvObj(jsonRoot.object(store->printStorePath(drvPath)));
+            json& drvObj = jsonRoot[store->printStorePath(drvPath)];
 
             auto drv = store->readDerivation(drvPath);
 
             {
-                auto outputsObj(drvObj.object("outputs"));
+                json& outputsObj = drvObj["outputs"];
+                outputsObj = json::object();
                 for (auto & [_outputName, output] : drv.outputs) {
                     auto & outputName = _outputName; // work around clang bug
-                    auto outputObj { outputsObj.object(outputName) };
+                    auto& outputObj = outputsObj[outputName];
+                    outputObj = json::object();
                     std::visit(overloaded {
                         [&](const DerivationOutput::InputAddressed & doi) {
-                            outputObj.attr("path", store->printStorePath(doi.path));
+                            outputObj["path"] = store->printStorePath(doi.path);
                         },
                         [&](const DerivationOutput::CAFixed & dof) {
-                            outputObj.attr("path", store->printStorePath(dof.path(*store, drv.name, outputName)));
-                            outputObj.attr("hashAlgo", dof.hash.printMethodAlgo());
-                            outputObj.attr("hash", dof.hash.hash.to_string(Base16, false));
+                            outputObj["path"] = store->printStorePath(dof.path(*store, drv.name, outputName));
+                            outputObj["hashAlgo"] = dof.hash.printMethodAlgo();
+                            outputObj["hash"] = dof.hash.hash.to_string(Base16, false);
                         },
                         [&](const DerivationOutput::CAFloating & dof) {
-                            outputObj.attr("hashAlgo", makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType));
+                            outputObj["hashAlgo"] = makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType);
                         },
                         [&](const DerivationOutput::Deferred &) {},
                         [&](const DerivationOutput::Impure & doi) {
-                            outputObj.attr("hashAlgo", makeFileIngestionPrefix(doi.method) + printHashType(doi.hashType));
-                            outputObj.attr("impure", true);
+                            outputObj["hashAlgo"] = makeFileIngestionPrefix(doi.method) + printHashType(doi.hashType);
+                            outputObj["impure"] = true;
                         },
                     }, output.raw());
                 }
             }
 
             {
-                auto inputsList(drvObj.list("inputSrcs"));
+                auto& inputsList = drvObj["inputSrcs"];
+                inputsList = json::array();
                 for (auto & input : drv.inputSrcs)
-                    inputsList.elem(store->printStorePath(input));
-            }
-
-            {
-                auto inputDrvsObj(drvObj.object("inputDrvs"));
-                for (auto & input : drv.inputDrvs) {
-                    auto inputList(inputDrvsObj.list(store->printStorePath(input.first)));
-                    for (auto & outputId : input.second)
-                        inputList.elem(outputId);
-                }
+                    inputsList.emplace_back(store->printStorePath(input));
             }
 
-            drvObj.attr("system", drv.platform);
-            drvObj.attr("builder", drv.builder);
-
             {
-                auto argsList(drvObj.list("args"));
-                for (auto & arg : drv.args)
-                    argsList.elem(arg);
+                auto& inputDrvsObj = drvObj["inputDrvs"];
+                inputDrvsObj = json::object();
+                for (auto & input : drv.inputDrvs)
+                    inputDrvsObj[store->printStorePath(input.first)] = input.second;
             }
 
-            {
-                auto envObj(drvObj.object("env"));
-                for (auto & var : drv.env)
-                    envObj.attr(var.first, var.second);
-            }
+            drvObj["system"] = drv.platform;
+            drvObj["builder"] = drv.builder;
+            drvObj["args"] = drv.args;
+            drvObj["env"] = drv.env;
         }
-
-        }
-
-        std::cout << "\n";
+        std::cout << jsonRoot.dump(2) << std::endl;
     }
 };