Merge pull request #4750 from NinjaTrappeur/nin-build-dry-run-json

nix build: make dry-run to print a json output if --json is enabled

src/nix/build.cc

@@ -54,6 +54,8 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
     {
         auto buildables = build(store, dryRun ? Realise::Nothing : Realise::Outputs, installables, buildMode);
 
+        if (json) logger->cout("%s", derivedPathsWithHintsToJSON(buildables, store).dump());
+
         if (dryRun) return;
 
         if (outLink != "")
@@ -79,8 +81,6 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
                 }
 
         updateProfile(buildables);
-
-        if (json) logger->cout("%s", derivedPathsWithHintsToJSON(buildables, store).dump());
     }
 };