Move value-only methods to `InstallableValue`

These methods would previously fail on the other `Installable`s, so
moving them to this class is more correct as to where they actually
work.

Additionally, a `InstallableValueCommand` is created to make it easier
(or rather no worse than before) to write commands that just work on
`InstallableValue`s.

Besides being a cleanup to avoid failing default methods, this gets us
closer to https://github.com/NixOS/rfcs/pull/134.

1 files changed, 30 insertions, 0 deletions

diff --git a/src/libcmd/installable-value.hh b/src/libcmd/installable-value.hh
index c6cdc4797..682c8d942 100644
--- a/src/libcmd/installable-value.hh
+++ b/src/libcmd/installable-value.hh
@@ -4,11 +4,41 @@
 
 namespace nix {
 
+struct App
+{
+    std::vector<DerivedPath> context;
+    Path program;
+    // FIXME: add args, sandbox settings, metadata, ...
+};
+
+struct UnresolvedApp
+{
+    App unresolved;
+    App resolve(ref<Store> evalStore, ref<Store> store);
+};
+
 struct InstallableValue : Installable
 {
     ref<EvalState> state;
 
     InstallableValue(ref<EvalState> state) : state(state) {}
+
+    virtual std::pair<Value *, PosIdx> toValue(EvalState & state) = 0;
+
+    /* Get a cursor to each value this Installable could refer to. However
+       if none exists, throw exception instead of returning empty vector. */
+    virtual std::vector<ref<eval_cache::AttrCursor>>
+    getCursors(EvalState & state);
+
+    /* Get the first and most preferred cursor this Installable could refer
+       to, or throw an exception if none exists. */
+    virtual ref<eval_cache::AttrCursor>
+    getCursor(EvalState & state);
+
+    UnresolvedApp toApp(EvalState & state);
+
+    static InstallableValue & require(Installable & installable);
+    static ref<InstallableValue> require(ref<Installable> installable);
 };
 
 }