Include the name in the JSON for derivations

This is non-breaking change in the to-JSON direction. This *is* a
breaking change in the from-JSON direction, but we don't care, as that
is brand new in this PR.

`nix show-derivation --help` currently has the sole public documentation
of this format, it is updated accordingly.

src/libstore/derivations.cc

@@ -988,6 +988,8 @@ nlohmann::json Derivation::toJSON(const Store & store) const
 {
     nlohmann::json res = nlohmann::json::object();
 
+    res["name"] = name;
+
     {
         nlohmann::json & outputsObj = res["outputs"];
         outputsObj = nlohmann::json::object();
@@ -1020,17 +1022,19 @@ nlohmann::json Derivation::toJSON(const Store & store) const
 
 
 Derivation Derivation::fromJSON(
-    const Store & store, std::string_view drvName,
+    const Store & store,
     const nlohmann::json & json)
 {
     Derivation res;
 
+    res.name = json["name"];
+
     {
         auto & outputsObj = json["outputs"];
         for (auto & [outputName, output] : outputsObj.items()) {
             res.outputs.insert_or_assign(
                 outputName,
-                DerivationOutput::fromJSON(store, drvName, outputName, output));
+                DerivationOutput::fromJSON(store, res.name, outputName, output));
         }
     }
 

src/libstore/derivations.hh

@@ -340,7 +340,6 @@ struct Derivation : BasicDerivation
     nlohmann::json toJSON(const Store & store) const;
     static Derivation fromJSON(
         const Store & store,
-        std::string_view drvName,
         const nlohmann::json & json);
 
     GENERATE_CMP(Derivation,

src/libstore/tests/derivation.cc

@@ -98,12 +98,12 @@ TEST_JSON(impure,
             Derivation { VAL },                                 \
             Derivation::fromJSON(                               \
                 *store,                                         \
-                DRV_NAME,                                       \
                 STR ## _json));                                 \
     }
 
 TEST_JSON(simple,
     R"({
+      "name": "my-derivation",
       "inputSrcs": [
         "/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"
       ],
@@ -126,6 +126,7 @@ TEST_JSON(simple,
     })",
     ({
         Derivation drv;
+        drv.name = "my-derivation";
         drv.inputSrcs = {
             store->parseStorePath("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"),
         };

src/nix/show-derivation.md

@@ -51,6 +51,9 @@ The JSON output is a JSON object whose keys are the store paths of the
 derivations, and whose values are a JSON object with the following
 fields:
 
+* `name`: The name of the derivation. This is used when calculating the
+  store paths of the derivation's outputs.
+
 * `outputs`: Information about the output paths of the
   derivation. This is a JSON object with one member per output, where
   the key is the output name and the value is a JSON object with these