give ExprInheritFrom a handle to what its standing in for

Change-Id: I12088e0b618407e5432523bbc97be63c8d6fce62

3 files changed, 16 insertions, 8 deletions

diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 418f888b3..703a32e8f 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -144,7 +144,10 @@ struct ExprVar : Expr
  */
 struct ExprInheritFrom : ExprVar
 {
-    ExprInheritFrom(PosIdx pos, Displacement displ): ExprVar(pos, {})
+    ref<Expr> fromExpr;
+
+    ExprInheritFrom(PosIdx pos, Displacement displ, ref<Expr> fromExpr)
+          : ExprVar(pos, {}), fromExpr(fromExpr)
     {
         this->level = 0;
         this->displ = displ;
@@ -222,7 +225,7 @@ struct ExprAttrs : Expr
     };
     typedef std::map<Symbol, AttrDef> AttrDefs;
     AttrDefs attrs;
-    std::unique_ptr<std::vector<std::unique_ptr<Expr>>> inheritFromExprs;
+    std::unique_ptr<std::vector<ref<Expr>>> inheritFromExprs;
     struct DynamicAttrDef {
         std::unique_ptr<Expr> nameExpr, valueExpr;
         PosIdx pos;
diff --git a/src/libexpr/parser/parser.cc b/src/libexpr/parser/parser.cc
index 850f1276e..e60cf967f 100644
--- a/src/libexpr/parser/parser.cc
+++ b/src/libexpr/parser/parser.cc
@@ -317,18 +317,23 @@ template<> struct BuildAST<grammar::inherit> : change_head<InheritState> {
                 });
             }
         }
-        if (auto fromE = std::move(s.from)) {
+        if (s.from != nullptr) {
             if (!b.attrs.inheritFromExprs)
-                b.attrs.inheritFromExprs = std::make_unique<std::vector<std::unique_ptr<Expr>>>();
-            b.attrs.inheritFromExprs->push_back(std::move(fromE));
+                b.attrs.inheritFromExprs = std::make_unique<std::vector<ref<Expr>>>();
+            auto fromExpr = ref<Expr>(std::move(s.from));
+            b.attrs.inheritFromExprs->push_back(fromExpr);
             for (auto & [i, iPos] : s.attrs) {
                 if (attrs.find(i.symbol) != attrs.end())
                     ps.dupAttr(i.symbol, iPos, attrs[i.symbol].pos);
-                auto from = std::make_unique<ExprInheritFrom>(s.fromPos, b.attrs.inheritFromExprs->size() - 1);
+                auto inheritFrom = std::make_unique<ExprInheritFrom>(
+                    s.fromPos,
+                    b.attrs.inheritFromExprs->size() - 1,
+                    fromExpr
+                );
                 attrs.emplace(
                     i.symbol,
                     ExprAttrs::AttrDef(
-                        std::make_unique<ExprSelect>(iPos, std::move(from), i.symbol),
+                        std::make_unique<ExprSelect>(iPos, std::move(inheritFrom), i.symbol),
                         iPos,
                         ExprAttrs::AttrDef::Kind::InheritedFrom));
             }
diff --git a/src/libexpr/parser/state.hh b/src/libexpr/parser/state.hh
index f5a0428d7..29889152e 100644
--- a/src/libexpr/parser/state.hh
+++ b/src/libexpr/parser/state.hh
@@ -103,7 +103,7 @@ inline void State::addAttr(ExprAttrs * attrs, AttrPath && attrPath, std::unique_
             auto * jAttrs = dynamic_cast<ExprAttrs *>(j->second.e.get());
             if (jAttrs && ae) {
                 if (ae->inheritFromExprs && !jAttrs->inheritFromExprs)
-                    jAttrs->inheritFromExprs = std::make_unique<std::vector<std::unique_ptr<Expr>>>();
+                    jAttrs->inheritFromExprs = std::make_unique<std::vector<ref<Expr>>>();
                 for (auto & ad : ae->attrs) {
                     auto j2 = jAttrs->attrs.find(ad.first);
                     if (j2 != jAttrs->attrs.end()) // Attr already defined in iAttrs, error.