Add a new Cmd type working on RealisedPaths

Where a `RealisedPath` is a store path with its history, meaning either
an opaque path for stuff that has been directly added to the store, or a
`Realisation` for stuff that has been built by a derivation

This is a low-level refactoring that doesn't bring anything by itself
(except a few dozen extra lines of code :/ ), but raising the
abstraction level a bit is important on a number of levels:

- Commands like `nix build` have to query for the realisations after the
  build is finished which is fragile (see
  27905f12e4a7207450abe37c9ed78e31603b67e1 for example). Having them
  oprate directly at the realisation level would avoid that
- Others like `nix copy` currently operate directly on (built) store
  paths, but need a bit more information as they will need to register
  the realisations on the remote side

1 files changed, 20 insertions, 3 deletions

diff --git a/src/libcmd/command.hh b/src/libcmd/command.hh
index ed6980075..8c0b3a94a 100644
--- a/src/libcmd/command.hh
+++ b/src/libcmd/command.hh
@@ -141,7 +141,7 @@ private:
 };
 
 /* A command that operates on zero or more store paths. */
-struct StorePathsCommand : public InstallablesCommand
+struct RealisedPathsCommand : public InstallablesCommand
 {
 private:
 
@@ -154,17 +154,28 @@ protected:
 
 public:
 
-    StorePathsCommand(bool recursive = false);
+    RealisedPathsCommand(bool recursive = false);
 
     using StoreCommand::run;
 
-    virtual void run(ref<Store> store, std::vector<StorePath> storePaths) = 0;
+    virtual void run(ref<Store> store, std::vector<RealisedPath> paths) = 0;
 
     void run(ref<Store> store) override;
 
     bool useDefaultInstallables() override { return !all; }
 };
 
+struct StorePathsCommand : public RealisedPathsCommand
+{
+    StorePathsCommand(bool recursive = false);
+
+    using RealisedPathsCommand::run;
+
+    virtual void run(ref<Store> store, std::vector<StorePath> storePaths) = 0;
+
+    void run(ref<Store> store, std::vector<RealisedPath> paths) override;
+};
+
 /* A command that operates on exactly one store path. */
 struct StorePathCommand : public InstallablesCommand
 {
@@ -218,6 +229,12 @@ std::set<StorePath> toDerivations(ref<Store> store,
     std::vector<std::shared_ptr<Installable>> installables,
     bool useDeriver = false);
 
+std::set<RealisedPath> toRealisedPaths(
+    ref<Store> store,
+    Realise mode,
+    OperateOn operateOn,
+    std::vector<std::shared_ptr<Installable>> installables);
+
 /* Helper function to generate args that invoke $EDITOR on
    filename:lineno. */
 Strings editorFor(const Pos & pos);