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/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);
-}
-
-
-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>() };
-    }
+    }, t);
 }
 
 }

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) {