Make InstallableFlake::toValue() and toDerivation() behave consistently

In particular, this means that 'nix eval` (which uses toValue()) no
longer auto-calls functions or functors (because
AttrCursor::findAlongAttrPath() doesn't).

Fixes #6152.

Also use ref<> in a few places, and don't return attrpaths from
getCursor() because cursors already have a getAttrPath() method.

2 files changed, 5 insertions, 3 deletions

diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index 54fa9b741..7d3fd01a4 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -306,9 +306,9 @@ Value * EvalCache::getRootValue()
     return *value;
 }
 
-std::shared_ptr<AttrCursor> EvalCache::getRoot()
+ref<AttrCursor> EvalCache::getRoot()
 {
-    return std::make_shared<AttrCursor>(ref(shared_from_this()), std::nullopt);
+    return make_ref<AttrCursor>(ref(shared_from_this()), std::nullopt);
 }
 
 AttrCursor::AttrCursor(
diff --git a/src/libexpr/eval-cache.hh b/src/libexpr/eval-cache.hh
index c9a9bf471..b0709ebc2 100644
--- a/src/libexpr/eval-cache.hh
+++ b/src/libexpr/eval-cache.hh
@@ -33,7 +33,7 @@ public:
         EvalState & state,
         RootLoader rootLoader);
 
-    std::shared_ptr<AttrCursor> getRoot();
+    ref<AttrCursor> getRoot();
 };
 
 enum AttrType {
@@ -104,6 +104,8 @@ public:
 
     ref<AttrCursor> getAttr(std::string_view name);
 
+    /* Get an attribute along a chain of attrsets. Note that this does
+       not auto-call functors or functions. */
     OrSuggestions<ref<AttrCursor>> findAlongAttrPath(const std::vector<Symbol> & attrPath, bool force = false);
 
     std::string getString();