libexpr: store inherit source exprs in a list, not vec

it's a surprise tool that will help us later!

Change-Id: Ieac785b00b3d14e5937c03fb2c97c918f4646e56

lix/libexpr/nixexpr.cc

@@ -130,12 +130,19 @@ void ExprAttrs::addBindingsToJSON(JSON & out, const SymbolTable & symbols) const
         }
     }
 
+    std::vector<Expr *> inheritFromExprs;
+    if (this->inheritFromExprs) {
+        for (auto & e : *this->inheritFromExprs) {
+            inheritFromExprs.push_back(e.get());
+        }
+    }
+
     for (const auto & [from, syms] : inheritsFrom) {
         JSON attrs = JSON::array();
         for (auto sym : syms)
             attrs.push_back(symbols[sym]);
         out["inheritFrom"].push_back({
-            {"from", (*inheritFromExprs)[from]->toJSON(symbols)},
+            {"from", inheritFromExprs[from]->toJSON(symbols)},
             {"attrs", attrs}
         });
     }

lix/libexpr/nixexpr.hh

@@ -151,10 +151,10 @@ struct ExprVar : Expr
  */
 struct ExprInheritFrom : Expr
 {
-    ref<Expr> fromExpr;
+    Expr & fromExpr;
     Displacement displ;
 
-    ExprInheritFrom(PosIdx pos, Displacement displ, ref<Expr> fromExpr)
+    ExprInheritFrom(PosIdx pos, Displacement displ, Expr & fromExpr)
           : Expr(pos), fromExpr(fromExpr), displ(displ)
     {
     }
@@ -238,7 +238,7 @@ struct ExprAttrs
     };
     typedef std::map<Symbol, AttrDef> AttrDefs;
     AttrDefs attrs;
-    std::unique_ptr<std::vector<ref<Expr>>> inheritFromExprs;
+    std::unique_ptr<std::list<std::unique_ptr<Expr>>> inheritFromExprs;
     struct DynamicAttrDef {
         std::unique_ptr<Expr> nameExpr, valueExpr;
         PosIdx pos;

lix/libexpr/parser/parser-impl1.inc.cc

@@ -398,16 +398,16 @@ template<> struct BuildAST<grammar::v1::inherit> : change_head<InheritState> {
         }
         if (s.from != nullptr) {
             if (!b.attrs.inheritFromExprs)
-                b.attrs.inheritFromExprs = std::make_unique<std::vector<ref<Expr>>>();
-            auto fromExpr = ref<Expr>::unsafeFromPtr(std::move(s.from));
-            b.attrs.inheritFromExprs->push_back(fromExpr);
+                b.attrs.inheritFromExprs = std::make_unique<std::list<std::unique_ptr<Expr>>>();
+            b.attrs.inheritFromExprs->push_back(std::move(s.from));
+            auto & fromExpr = b.attrs.inheritFromExprs->back();
             for (auto & i : s.attrs) {
                 if (attrs.find(i.symbol) != attrs.end())
                     ps.dupAttr(i.symbol, i.pos, attrs[i.symbol].pos);
                 auto inheritFrom = std::make_unique<ExprInheritFrom>(
                     s.fromPos,
                     b.attrs.inheritFromExprs->size() - 1,
-                    fromExpr
+                    *fromExpr
                 );
                 attrs.emplace(
                     i.symbol,

lix/libexpr/parser/state.hh

@@ -173,7 +173,7 @@ inline void State::addAttr(ExprAttrs * attrs, AttrPath && attrPath, std::unique_
             auto * jAttrs = dynamic_cast<ExprSet *>(j->second.e.get());
             if (jAttrs && ae) {
                 if (ae->inheritFromExprs && !jAttrs->inheritFromExprs)
-                    jAttrs->inheritFromExprs = std::make_unique<std::vector<ref<Expr>>>();
+                    jAttrs->inheritFromExprs = std::make_unique<std::list<std::unique_ptr<Expr>>>();
                 for (auto & ad : ae->attrs) {
                     auto j2 = jAttrs->attrs.find(ad.first);
                     if (j2 != jAttrs->attrs.end()) // Attr already defined in iAttrs, error.