NixOS · Ericson2314 · Jul 30, 2025 · May 26, 2025
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
@@ -1363,7 +1363,7 @@ static void derivationStrictInternal(EvalState & state, std::string_view drvName
 
     /* Check whether attributes should be passed as a JSON file. */
     using nlohmann::json;
-    std::optional<json> jsonObject;
+    std::optional<StructuredAttrs> jsonObject;
     auto pos = v.determinePos(noPos);
     auto attr = attrs->find(state.sStructuredAttrs);
     if (attr != attrs->end()
@@ -1372,7 +1372,7 @@ static void derivationStrictInternal(EvalState & state, std::string_view drvName
             pos,
             "while evaluating the `__structuredAttrs` "
             "attribute passed to builtins.derivationStrict"))
-        jsonObject = json::object();
+        jsonObject = StructuredAttrs{.structuredAttrs = json::object()};
 
     /* Check whether null attributes should be ignored. */
     bool ignoreNulls = false;
@@ -1484,7 +1484,7 @@ static void derivationStrictInternal(EvalState & state, std::string_view drvName
                     if (i->name == state.sStructuredAttrs)
                         continue;
 
-                    jsonObject->emplace(key, printValueAsJSON(state, true, *i->value, pos, context));
+                    jsonObject->structuredAttrs.emplace(key, printValueAsJSON(state, true, *i->value, pos, context));
 
                     if (i->name == state.sBuilder)
                         drv.builder = state.forceString(*i->value, context, pos, context_below);
@@ -1532,23 +1532,26 @@ static void derivationStrictInternal(EvalState & state, std::string_view drvName
 
                 } else {
                     auto s = state.coerceToString(pos, *i->value, context, context_below, true).toOwned();
-                    drv.env.emplace(key, s);
-                    if (i->name == state.sBuilder)
-                        drv.builder = std::move(s);
-                    else if (i->name == state.sSystem)
-                        drv.platform = std::move(s);
-                    else if (i->name == state.sOutputHash)
-                        outputHash = std::move(s);
-                    else if (i->name == state.sOutputHashAlgo)
-                        outputHashAlgo = parseHashAlgoOpt(s);
-                    else if (i->name == state.sOutputHashMode)
-                        handleHashMode(s);
-                    else if (i->name == state.sOutputs)
-                        handleOutputs(tokenizeString<Strings>(s));
-                    else if (i->name == state.sJson)
+                    if (i->name == state.sJson) {
                         warn(
                             "In derivation '%s': setting structured attributes via '__json' is deprecated, and may be disallowed in future versions of Nix. Set '__structuredAttrs = true' instead.",
                             drvName);
+                        drv.structuredAttrs = StructuredAttrs::parse(s);
+                    } else {
+                        drv.env.emplace(key, s);
+                        if (i->name == state.sBuilder)
+                            drv.builder = std::move(s);
+                        else if (i->name == state.sSystem)
+                            drv.platform = std::move(s);
+                        else if (i->name == state.sOutputHash)
+                            outputHash = std::move(s);
+                        else if (i->name == state.sOutputHashAlgo)
+                            outputHashAlgo = parseHashAlgoOpt(s);
+                        else if (i->name == state.sOutputHashMode)
+                            handleHashMode(s);
+                        else if (i->name == state.sOutputs)
+                            handleOutputs(tokenizeString<Strings>(s));
+                    }
                 }
             }
 
@@ -1560,8 +1563,10 @@ static void derivationStrictInternal(EvalState & state, std::string_view drvName
     }
 
     if (jsonObject) {
-        drv.env.emplace("__json", jsonObject->dump());
-        jsonObject.reset();
+        /* The only other way `drv.structuredAttrs` can be set is when
+           `jsonObject` is not set. */
+        assert(!drv.structuredAttrs);
+        drv.structuredAttrs = std::move(*jsonObject);
     }
 
     /* Everything in the context of the strings in the derivation

@@ -108,10 +108,9 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_defaults)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
-        EXPECT_TRUE(!parsedDrv);
+        EXPECT_TRUE(!got.structuredAttrs);
 
         EXPECT_EQ(options.additionalSandboxProfile, "");
         EXPECT_EQ(options.noChroot, false);
@@ -143,8 +142,7 @@ TEST_F(DerivationAdvancedAttrsTest, advancedAttributes_defaults)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
         EXPECT_EQ(options.getRequiredSystemFeatures(got), StringSet{});
     });
@@ -157,8 +155,7 @@ TEST_F(CaDerivationAdvancedAttrsTest, advancedAttributes_defaults)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
         EXPECT_EQ(options.getRequiredSystemFeatures(got), StringSet{"ca-derivations"});
     });
@@ -171,10 +168,9 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
-        EXPECT_TRUE(!parsedDrv);
+        EXPECT_TRUE(!got.structuredAttrs);
 
         EXPECT_EQ(options.additionalSandboxProfile, "sandcastle");
         EXPECT_EQ(options.noChroot, true);
@@ -195,8 +191,7 @@ TEST_F(DerivationAdvancedAttrsTest, advancedAttributes)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
         EXPECT_EQ(
             options.exportReferencesGraph,
@@ -245,8 +240,7 @@ TEST_F(CaDerivationAdvancedAttrsTest, advancedAttributes)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
         EXPECT_EQ(
             options.exportReferencesGraph,
@@ -298,10 +292,9 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_structuredAttrs_d
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
-        EXPECT_TRUE(parsedDrv);
+        EXPECT_TRUE(got.structuredAttrs);
 
         EXPECT_EQ(options.additionalSandboxProfile, "");
         EXPECT_EQ(options.noChroot, false);
@@ -332,8 +325,7 @@ TEST_F(DerivationAdvancedAttrsTest, advancedAttributes_structuredAttrs_defaults)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
         EXPECT_EQ(options.getRequiredSystemFeatures(got), StringSet{});
     });
@@ -346,8 +338,7 @@ TEST_F(CaDerivationAdvancedAttrsTest, advancedAttributes_structuredAttrs_default
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
         EXPECT_EQ(options.getRequiredSystemFeatures(got), StringSet{"ca-derivations"});
     });
@@ -360,10 +351,9 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_structuredAttrs)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
-        EXPECT_TRUE(parsedDrv);
+        EXPECT_TRUE(got.structuredAttrs);
 
         EXPECT_EQ(options.additionalSandboxProfile, "sandcastle");
         EXPECT_EQ(options.noChroot, true);
@@ -394,8 +384,7 @@ TEST_F(DerivationAdvancedAttrsTest, advancedAttributes_structuredAttrs)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
         EXPECT_EQ(
             options.exportReferencesGraph,
@@ -448,8 +437,7 @@ TEST_F(CaDerivationAdvancedAttrsTest, advancedAttributes_structuredAttrs)
 
         auto drvPath = writeDerivation(*this->store, got, NoRepair, true);
 
-        auto parsedDrv = StructuredAttrs::tryParse(got.env);
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, parsedDrv ? &*parsedDrv : nullptr);
+        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
 
         EXPECT_EQ(
             options.exportReferencesGraph,

@@ -222,7 +222,7 @@ Derivation makeSimpleDrv(const Store & store)
         "bar",
         "baz",
     };
-    drv.env = {
+    drv.env = StringPairs{
         {
             "BIG_BAD",
             "WOLF",
@@ -284,7 +284,7 @@ Derivation makeDynDepDerivation(const Store & store)
         "bar",
         "baz",
     };
-    drv.env = {
+    drv.env = StringPairs{
         {
             "BIG_BAD",
             "WOLF",

@@ -32,12 +32,9 @@ DerivationBuildingGoal::DerivationBuildingGoal(
 {
     drv = std::make_unique<Derivation>(drv_);
 
-    if (auto parsedOpt = StructuredAttrs::tryParse(drv->env)) {
-        parsedDrv = std::make_unique<StructuredAttrs>(*parsedOpt);
-    }
     try {
         drvOptions =
-            std::make_unique<DerivationOptions>(DerivationOptions::fromStructuredAttrs(drv->env, parsedDrv.get()));
+            std::make_unique<DerivationOptions>(DerivationOptions::fromStructuredAttrs(drv->env, drv->structuredAttrs));
     } catch (Error & e) {
         e.addTrace({}, "while parsing derivation '%s'", worker.store.printStorePath(drvPath));
         throw;
@@ -661,7 +658,6 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
                     buildMode,
                     buildResult,
                     *drv,
-                    parsedDrv.get(),
                     *drvOptions,
                     inputPaths,
                     initialOutputs,

@@ -63,9 +63,8 @@ Goal::Co DerivationGoal::haveDerivation()
     trace("have derivation");
 
     auto drvOptions = [&]() -> DerivationOptions {
-        auto parsedOpt = StructuredAttrs::tryParse(drv->env);
         try {
-            return DerivationOptions::fromStructuredAttrs(drv->env, parsedOpt ? &*parsedOpt : nullptr);
+            return DerivationOptions::fromStructuredAttrs(drv->env, drv->structuredAttrs);
         } catch (Error & e) {
             e.addTrace({}, "while parsing derivation '%s'", worker.store.printStorePath(drvPath));
             throw;

@@ -92,6 +92,12 @@ using OutputChecks = DerivationOptions::OutputChecks;
 
 using OutputChecksVariant = std::variant<OutputChecks, std::map<std::string, OutputChecks>>;
 
+DerivationOptions DerivationOptions::fromStructuredAttrs(
+    const StringMap & env, const std::optional<StructuredAttrs> & parsed, bool shouldWarn)
+{
+    return fromStructuredAttrs(env, parsed ? &*parsed : nullptr);
+}
+
 DerivationOptions
 DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAttrs * parsed, bool shouldWarn)
 {

@@ -452,6 +452,7 @@ Derivation parseDerivation(
         expect(str, ")");
         drv.env.insert_or_assign(std::move(name), std::move(value));
     }
+    drv.structuredAttrs = StructuredAttrs::tryExtract(drv.env);
 
     expect(str, ")");
     return drv;
@@ -685,16 +686,28 @@ std::string Derivation::unparse(
 
     s += ",[";
     first = true;
-    for (auto & i : env) {
-        if (first)
-            first = false;
-        else
+
+    auto unparseEnv = [&](const StringPairs atermEnv) {
+        for (auto & i : atermEnv) {
+            if (first)
+                first = false;
+            else
+                s += ',';
+            s += '(';
+            printString(s, i.first);
             s += ',';
-        s += '(';
-        printString(s, i.first);
-        s += ',';
-        printString(s, maskOutputs && outputs.count(i.first) ? "" : i.second);
-        s += ')';
+            printString(s, maskOutputs && outputs.count(i.first) ? "" : i.second);
+            s += ')';
+        }
+    };
+
+    StructuredAttrs::checkKeyNotInUse(env);
+    if (structuredAttrs) {
+        StringPairs scratch = env;
+        scratch.insert(structuredAttrs->unparse());
+        unparseEnv(scratch);
+    } else {
+        unparseEnv(env);
     }
 
     s += "])";
@@ -948,6 +961,7 @@ Source & readDerivation(Source & in, const StoreDirConfig & store, BasicDerivati
         auto value = readString(in);
         drv.env[key] = value;
     }
+    drv.structuredAttrs = StructuredAttrs::tryExtract(drv.env);
 
     return in;
 }
@@ -983,9 +997,21 @@ void writeDerivation(Sink & out, const StoreDirConfig & store, const BasicDeriva
     }
     CommonProto::write(store, CommonProto::WriteConn{.to = out}, drv.inputSrcs);
     out << drv.platform << drv.builder << drv.args;
-    out << drv.env.size();
-    for (auto & i : drv.env)
-        out << i.first << i.second;
+
+    auto writeEnv = [&](const StringPairs atermEnv) {
+        out << atermEnv.size();
+        for (auto & [k, v] : atermEnv)
+            out << k << v;
+    };
+
+    StructuredAttrs::checkKeyNotInUse(drv.env);
+    if (drv.structuredAttrs) {
+        StringPairs scratch = drv.env;
+        scratch.insert(drv.structuredAttrs->unparse());
+        writeEnv(scratch);
+    } else {
+        writeEnv(drv.env);
+    }
 }
 
 std::string hashPlaceholder(const OutputNameView outputName)
@@ -1017,6 +1043,17 @@ void BasicDerivation::applyRewrites(const StringMap & rewrites)
         newEnv.emplace(envName, envValue);
     }
     env = std::move(newEnv);
+
+    if (structuredAttrs) {
+        // TODO rewrite the JSON AST properly, rather than dump parse round trip.
+        auto [k, jsonS] = structuredAttrs->unparse();
+        jsonS = rewriteStrings(jsonS, rewrites);
+        StringPairs newEnv;
+        newEnv.insert(std::pair{k, std::move(jsonS)});
+        auto newStructuredAttrs = StructuredAttrs::tryExtract(newEnv);
+        assert(newStructuredAttrs);
+        structuredAttrs = std::move(*newStructuredAttrs);
+    }
 }
 
 static void rewriteDerivation(Store & store, BasicDerivation & drv, const StringMap & rewrites)
@@ -1338,10 +1375,8 @@ nlohmann::json Derivation::toJSON(const StoreDirConfig & store) const
     res["args"] = args;
     res["env"] = env;
 
-    if (auto it = env.find("__json"); it != env.end()) {
-        res["env"].erase("__json");
-        res["structuredAttrs"] = nlohmann::json::parse(it->second);
-    }
+    if (structuredAttrs)
+        res["structuredAttrs"] = structuredAttrs->structuredAttrs;
 
     return res;
 }
@@ -1411,7 +1446,7 @@ Derivation Derivation::fromJSON(
     }
 
     if (auto structuredAttrs = get(json, "structuredAttrs"))
-        res.env.insert_or_assign("__json", structuredAttrs->dump());
+        res.structuredAttrs = StructuredAttrs{*structuredAttrs};
 
     return res;
 }