From 512afd8b7a68f8226443a8df378f5208464435ef Mon Sep 17 00:00:00 2001
From: regnat <rg@regnat.ovh>
Date: Thu, 3 Jun 2021 15:29:43 +0200
Subject: [PATCH] Use the cache in the outer shell
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Make sure that we don’t discard it before entering the evaluator proper
---
 src/libcmd/installables.cc | 10 ++++------
 src/libexpr/attr-path.cc   | 11 +++++++----
 src/libexpr/eval.hh        |  2 ++
 3 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index fe52912cf..cdd965b9a 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -428,12 +428,10 @@ Value * InstallableFlake::getFlakeOutputs(EvalState & state, const flake::Locked
 
     callFlake(state, lockedFlake, *vFlake);
 
-    auto aOutputs = vFlake->attrs->get(state.symbols.create("outputs"));
-    assert(aOutputs);
-
-    state.forceValue(*aOutputs->value);
-
-    return aOutputs->value;
+    auto vRes = state.allocValue();
+    auto gotField = state.getAttrField(*vFlake, {state.symbols.create("outputs")}, noPos, *vRes);
+    assert(gotField);
+    return vRes;
 }
 
 ref<eval_cache::EvalCache> openEvalCache(
diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index 9dd557205..9c3c1fc4b 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -73,11 +73,14 @@ std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const string & attr
             if (attr.empty())
                 throw Error("empty attribute name in selection path '%1%'", attrPath);
 
-            Bindings::iterator a = v->attrs->find(state.symbols.create(attr));
-            if (a == v->attrs->end())
+            auto v2 = state.allocValue();
+            auto gotField = state.getAttrField(*v, {state.symbols.create(attr)}, pos, *v2);
+            if (!gotField)
                 throw AttrPathNotFound("attribute '%1%' in selection path '%2%' not found", attr, attrPath);
-            v = &*a->value;
-            pos = *a->pos;
+            v = v2;
+            /* Bindings::iterator a = v->attrs->find(state.symbols.create(attr)); */
+            /* v = &*a->value; */
+            /* pos = *a->pos; */
         }
 
         else {
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 36a3b5b74..a86585035 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -353,6 +353,8 @@ private:
     friend void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v);
     friend void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v);
 
+public:
+
     bool getAttrField(Value & attrs, const std::vector<Symbol> & selector, const Pos & pos, Value & dest);
 };