Enfore the use of properly built paths in libcmd

Replace `DerivedPathWithHints` by a new `BuiltPath` type that serves as
a proof that the corresponding path has been built.

src/libstore/derived-path.cc

@@ -15,11 +15,26 @@ nlohmann::json BuiltPath::Built::toJSON(ref<Store> store) const {
     nlohmann::json res;
     res["drvPath"] = store->printStorePath(drvPath);
     for (const auto& [output, path] : outputs) {
-        res["outputs"][output] = path ? store->printStorePath(*path) : "";
+        res["outputs"][output] = store->printStorePath(path);
     }
     return res;
 }
 
+StorePathSet BuiltPath::outPaths() const
+{
+    return std::visit(
+        overloaded{
+            [](BuiltPath::Opaque p) { return StorePathSet{p.path}; },
+            [](BuiltPath::Built b) {
+                StorePathSet res;
+                for (auto & [_, path] : b.outputs)
+                    res.insert(path);
+                return res;
+            },
+        }, raw()
+    );
+}
+
 nlohmann::json derivedPathsWithHintsToJSON(const BuiltPaths & buildables, ref<Store> store) {
     auto res = nlohmann::json::array();
     for (const BuiltPath & buildable : buildables) {
@@ -74,4 +89,30 @@ DerivedPath DerivedPath::parse(const Store & store, std::string_view s)
         : (DerivedPath) DerivedPath::Built::parse(store, s);
 }
 
+RealisedPath::Set BuiltPath::toRealisedPaths(Store & store) const
+{
+    RealisedPath::Set res;
+    std::visit(
+        overloaded{
+            [&](BuiltPath::Opaque p) { res.insert(p.path); },
+            [&](BuiltPath::Built p) {
+                auto drvHashes =
+                    staticOutputHashes(store, store.readDerivation(p.drvPath));
+                for (auto& [outputName, outputPath] : p.outputs) {
+                    if (settings.isExperimentalFeatureEnabled(
+                            "ca-derivations")) {
+                        auto thisRealisation = store.queryRealisation(
+                            DrvOutput{drvHashes.at(outputName), outputName});
+                        assert(thisRealisation);  // We’ve built it, so we must h
+                                                  // ve the realisation
+                        res.insert(*thisRealisation);
+                    } else {
+                        res.insert(outputPath);
+                    }
+                }
+            },
+        },
+        raw());
+    return res;
+}
 }

src/libstore/derived-path.hh

@@ -2,6 +2,7 @@
 
 #include "util.hh"
 #include "path.hh"
+#include "realisation.hh"
 
 #include <optional>
 
@@ -83,7 +84,7 @@ struct DerivedPath : _DerivedPathRaw {
  */
 struct BuiltPathBuilt {
     StorePath drvPath;
-    std::map<std::string, std::optional<StorePath>> outputs;
+    std::map<std::string, StorePath> outputs;
 
     nlohmann::json toJSON(ref<Store> store) const;
     static BuiltPathBuilt parse(const Store & store, std::string_view);
@@ -95,20 +96,9 @@ using _BuiltPathRaw = std::variant<
 >;
 
 /**
- * A derived path with hints in the form of optional concrete output paths in the built case.
- *
- * This type is currently just used by the CLI. The paths are filled in
- * during evaluation for derivations that know what paths they will
- * produce in advanced, i.e. input-addressed or fixed-output content
- * addressed derivations.
- *
- * That isn't very good, because it puts floating content-addressed
- * derivations "at a disadvantage". It would be better to never rely on
- * the output path of unbuilt derivations, and exclusively use the
- * realizations types to work with built derivations' concrete output
- * paths.
+ * A built path. Similar to a `DerivedPath`, but enriched with the corresponding
+ * output path(s).
  */
-// FIXME Stop using and delete this, or if that is not possible move out of libstore to libcmd.
 struct BuiltPath : _BuiltPathRaw {
     using Raw = _BuiltPathRaw;
     using Raw::Raw;
@@ -120,8 +110,12 @@ struct BuiltPath : _BuiltPathRaw {
         return static_cast<const Raw &>(*this);
     }
 
+    StorePathSet outPaths() const;
+    RealisedPath::Set toRealisedPaths(Store & store) const;
+
 };
 
+typedef std::vector<DerivedPath> DerivedPaths;
 typedef std::vector<BuiltPath> BuiltPaths;
 
 nlohmann::json derivedPathsWithHintsToJSON(const BuiltPaths & buildables, ref<Store> store);