Remove default constructor from OutputsSpec

This forces us to be explicit.

It also requires to rework how `from_json` works. A `JSON_IMPL` is added
to assist with this.

src/libcmd/installables.cc

@@ -827,7 +827,7 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
                             return storePath.isDerivation()
                                 ? (DerivedPath) DerivedPath::Built {
                                     .drvPath = std::move(storePath),
-                                    .outputs = {},
+                                    .outputs = OutputsSpec::All {},
                                 }
                                 : (DerivedPath) DerivedPath::Opaque {
                                     .path = std::move(storePath),

src/libcmd/repl.cc

@@ -641,7 +641,12 @@ bool NixRepl::processLine(std::string line)
         Path drvPathRaw = state->store->printStorePath(drvPath);
 
         if (command == ":b" || command == ":bl") {
-            state->store->buildPaths({DerivedPath::Built{drvPath}});
+            state->store->buildPaths({
+                DerivedPath::Built {
+                    .drvPath = drvPath,
+                    .outputs = OutputsSpec::All { },
+                },
+            });
             auto drv = state->store->readDerivation(drvPath);
             logger->cout("\nThis derivation produced the following outputs:");
             for (auto & [outputName, outputPath] : state->store->queryDerivationOutputMap(drvPath)) {

src/libstore/build/entry-points.cc

@@ -80,7 +80,7 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
     BuildMode buildMode)
 {
     Worker worker(*this, *this);
-    auto goal = worker.makeBasicDerivationGoal(drvPath, drv, {}, buildMode);
+    auto goal = worker.makeBasicDerivationGoal(drvPath, drv, OutputsSpec::All {}, buildMode);
 
     try {
         worker.run(Goals{goal});
@@ -89,7 +89,10 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
         return BuildResult {
             .status = BuildResult::MiscFailure,
             .errorMsg = e.msg(),
-            .path = DerivedPath::Built { .drvPath = drvPath },
+            .path = DerivedPath::Built {
+                .drvPath = drvPath,
+                .outputs = OutputsSpec::All { },
+            },
         };
     };
 }

src/libstore/legacy-ssh-store.cc

@@ -279,7 +279,12 @@ public:
 
         conn->to.flush();
 
-        BuildResult status { .path = DerivedPath::Built { .drvPath = drvPath } };
+        BuildResult status {
+            .path = DerivedPath::Built {
+                .drvPath = drvPath,
+                .outputs = OutputsSpec::All { },
+            },
+        };
         status.status = (BuildResult::Status) readInt(conn->from);
         conn->from >> status.errorMsg;
 

src/libstore/outputs-spec.cc

@@ -110,9 +110,21 @@ bool OutputsSpec::merge(const OutputsSpec & that)
     }, raw());
 }
 
+}
 
-void to_json(nlohmann::json & json, const OutputsSpec & outputsSpec)
+namespace nlohmann {
-{
+
+using namespace nix;
+
+OutputsSpec adl_serializer<OutputsSpec>::from_json(const json & json) {
+    auto names = json.get<StringSet>();
+    if (names == StringSet({"*"}))
+        return OutputsSpec::All {};
+    else
+        return OutputsSpec::Names { std::move(names) };
+}
+
+void adl_serializer<OutputsSpec>::to_json(json & json, OutputsSpec t) {
     std::visit(overloaded {
         [&](const OutputsSpec::All &) {
             json = std::vector<std::string>({"*"});
@@ -120,40 +132,27 @@ void to_json(nlohmann::json & json, const OutputsSpec & outputsSpec)
         [&](const OutputsSpec::Names & names) {
             json = names;
         },
-    }, outputsSpec);
+    }, t);
 }
 
 
-void to_json(nlohmann::json & json, const ExtendedOutputsSpec & extendedOutputsSpec)
+ExtendedOutputsSpec adl_serializer<ExtendedOutputsSpec>::from_json(const json & json) {
-{
+    if (json.is_null())
+        return ExtendedOutputsSpec::Default {};
+    else {
+        return ExtendedOutputsSpec::Explicit { json.get<OutputsSpec>() };
+    }
+}
+
+void adl_serializer<ExtendedOutputsSpec>::to_json(json & json, ExtendedOutputsSpec t) {
     std::visit(overloaded {
         [&](const ExtendedOutputsSpec::Default &) {
             json = nullptr;
         },
         [&](const ExtendedOutputsSpec::Explicit & e) {
-            to_json(json, e);
+            adl_serializer<OutputsSpec>::to_json(json, e);
         },
-    }, extendedOutputsSpec);
+    }, t);
-}
-
-
-void from_json(const nlohmann::json & json, OutputsSpec & outputsSpec)
-{
-    auto names = json.get<StringSet>();
-    if (names == StringSet({"*"}))
-        outputsSpec = OutputsSpec::All {};
-    else
-        outputsSpec = OutputsSpec::Names { std::move(names) };
-}
-
-
-void from_json(const nlohmann::json & json, ExtendedOutputsSpec & extendedOutputsSpec)
-{
-    if (json.is_null())
-        extendedOutputsSpec = ExtendedOutputsSpec::Default {};
-    else {
-        extendedOutputsSpec = ExtendedOutputsSpec::Explicit { json.get<OutputsSpec>() };
-    }
 }
 
 }

src/libstore/outputs-spec.hh

@@ -4,7 +4,7 @@
 #include <set>
 #include <variant>
 
-#include "nlohmann/json_fwd.hpp"
+#include "json-impls.hh"
 
 namespace nix {
 
@@ -35,6 +35,9 @@ struct OutputsSpec : _OutputsSpecRaw {
     using Raw = _OutputsSpecRaw;
     using Raw::Raw;
 
+    /* Force choosing a variant */
+    OutputsSpec() = delete;
+
     using Names = OutputNames;
     using All = AllOutputs;
 
@@ -85,11 +88,7 @@ struct ExtendedOutputsSpec : _ExtendedOutputsSpecRaw {
     std::string to_string() const;
 };
 
-
-void to_json(nlohmann::json &, const OutputsSpec &);
-void from_json(const nlohmann::json &, OutputsSpec &);
-
-void to_json(nlohmann::json &, const ExtendedOutputsSpec &);
-void from_json(const nlohmann::json &, ExtendedOutputsSpec &);
-
 }
+
+JSON_IMPL(OutputsSpec)
+JSON_IMPL(ExtendedOutputsSpec)

src/libstore/remote-store.cc

@@ -910,7 +910,12 @@ BuildResult RemoteStore::buildDerivation(const StorePath & drvPath, const BasicD
     writeDerivation(conn->to, *this, drv);
     conn->to << buildMode;
     conn.processStderr();
-    BuildResult res { .path = DerivedPath::Built { .drvPath = drvPath } };
+    BuildResult res {
+        .path = DerivedPath::Built {
+            .drvPath = drvPath,
+            .outputs = OutputsSpec::All { },
+        },
+    };
     res.status = (BuildResult::Status) readInt(conn->from);
     conn->from >> res.errorMsg;
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 29) {

src/libutil/json-impls.hh

@@ -0,0 +1,14 @@
+#pragma once
+
+#include "nlohmann/json_fwd.hpp"
+
+// Following https://github.com/nlohmann/json#how-can-i-use-get-for-non-default-constructiblenon-copyable-types
+#define JSON_IMPL(TYPE)                                                \
+    namespace nlohmann {                                               \
+        using namespace nix;                                           \
+        template <>                                                    \
+        struct adl_serializer<TYPE> {                                  \
+            static TYPE from_json(const json & json);                  \
+            static void to_json(json & json, TYPE t);                  \
+        };                                                             \
+    }

src/nix-env/nix-env.cc

@@ -478,9 +478,14 @@ static void printMissing(EvalState & state, DrvInfos & elems)
     std::vector<DerivedPath> targets;
     for (auto & i : elems)
         if (auto drvPath = i.queryDrvPath())
-            targets.push_back(DerivedPath::Built{*drvPath});
+            targets.push_back(DerivedPath::Built{
+                .drvPath = *drvPath,
+                .outputs = OutputsSpec::All { },
+            });
         else
-            targets.push_back(DerivedPath::Opaque{i.queryOutPath()});
+            targets.push_back(DerivedPath::Opaque{
+                .path = i.queryOutPath(),
+            });
 
     printMissing(state.store, targets);
 }
@@ -751,8 +756,13 @@ static void opSet(Globals & globals, Strings opFlags, Strings opArgs)
     auto drvPath = drv.queryDrvPath();
     std::vector<DerivedPath> paths {
         drvPath
-        ? (DerivedPath) (DerivedPath::Built { *drvPath })
+        ? (DerivedPath) (DerivedPath::Built {
-        : (DerivedPath) (DerivedPath::Opaque { drv.queryOutPath() }),
+            .drvPath = *drvPath,
+            .outputs = OutputsSpec::All { },
+        })
+        : (DerivedPath) (DerivedPath::Opaque {
+            .path = drv.queryOutPath(),
+        }),
     };
     printMissing(globals.state->store, paths);
     if (globals.dryRun) return;

src/nix/bundle.cc

@@ -105,7 +105,12 @@ struct CmdBundle : InstallableCommand
 
         auto outPath = evalState->coerceToStorePath(attr2->pos, *attr2->value, context2, "");
 
-        store->buildPaths({ DerivedPath::Built { drvPath } });
+        store->buildPaths({
+            DerivedPath::Built {
+                .drvPath = drvPath,
+                .outputs = OutputsSpec::All { },
+            },
+        });
 
         auto outPathS = store->printStorePath(outPath);
 

src/nix/develop.cc

@@ -232,7 +232,12 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
     auto shellDrvPath = writeDerivation(*evalStore, drv);
 
     /* Build the derivation. */
-    store->buildPaths({DerivedPath::Built{shellDrvPath}}, bmNormal, evalStore);
+    store->buildPaths(
+        { DerivedPath::Built {
+            .drvPath = shellDrvPath,
+            .outputs = OutputsSpec::All { },
+        }},
+        bmNormal, evalStore);
 
     for (auto & [_0, optPath] : evalStore->queryPartialDerivationOutputMap(shellDrvPath)) {
         assert(optPath);

src/nix/flake.cc

@@ -513,8 +513,12 @@ struct CmdFlakeCheck : FlakeCommand
                                     auto drvPath = checkDerivation(
                                         fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
                                         *attr2.value, attr2.pos);
-                                    if (drvPath && attr_name == settings.thisSystem.get())
+                                    if (drvPath && attr_name == settings.thisSystem.get()) {
-                                        drvPaths.push_back(DerivedPath::Built{*drvPath});
+                                        drvPaths.push_back(DerivedPath::Built {
+                                            .drvPath = *drvPath,
+                                            .outputs = OutputsSpec::All { },
+                                        });
+                                    }
                                 }
                             }
                         }