preserve information about whether/how an attribute was inherited

(cherry picked from commit c66ee57edc6cac3571bfbf77d0c0ea4d25b4e805)
Change-Id: Ie8606a8b2f5946c87dd4d16b7b46203e199a4cc1

5 files changed, 31 insertions, 13 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index bb3e6f3bd..bf4c917c6 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1238,11 +1238,11 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         Displacement displ = 0;
         for (auto & i : attrs) {
             Value * vAttr;
-            if (hasOverrides && !i.second.inherited) {
+            if (hasOverrides && !i.second.inherited()) {
                 vAttr = state.allocValue();
                 mkThunk(*vAttr, env2, i.second.e);
             } else
-                vAttr = i.second.e->maybeThunk(state, i.second.inherited ? env : env2);
+                vAttr = i.second.e->maybeThunk(state, i.second.inherited() ? env : env2);
             env2.values[displ++] = vAttr;
             v.attrs->push_back(Attr(i.first, vAttr, i.second.pos));
         }
@@ -1313,7 +1313,7 @@ void ExprLet::eval(EvalState & state, Env & env, Value & v)
        environment. */
     Displacement displ = 0;
     for (auto & i : attrs->attrs)
-        env2.values[displ++] = i.second.e->maybeThunk(state, i.second.inherited ? env : env2);
+        env2.values[displ++] = i.second.e->maybeThunk(state, i.second.inherited() ? env : env2);
 
     auto dts = state.debugRepl
         ? makeDebugTraceStacker(
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 3525ea1a3..a12fd62c0 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -80,7 +80,7 @@ void ExprAttrs::show(const SymbolTable & symbols, std::ostream & str) const
         return sa < sb;
     });
     for (auto & i : sorted) {
-        if (i->second.inherited)
+        if (i->second.inherited())
             str << "inherit " << symbols[i->first] << " " << "; ";
         else {
             str << symbols[i->first] << " = ";
@@ -151,7 +151,7 @@ void ExprLet::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "(let ";
     for (auto & i : attrs->attrs)
-        if (i.second.inherited) {
+        if (i.second.inherited()) {
             str << "inherit " << symbols[i.first] << "; ";
         }
         else {
@@ -341,7 +341,7 @@ void ExprAttrs::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv>
         // No need to sort newEnv since attrs is in sorted order.
 
         for (auto & i : attrs)
-            i.second.e->bindVars(es, i.second.inherited ? env : newEnv);
+            i.second.e->bindVars(es, i.second.inherited() ? env : newEnv);
 
         for (auto & i : dynamicAttrs) {
             i.nameExpr->bindVars(es, newEnv);
@@ -416,7 +416,7 @@ void ExprLet::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
     // No need to sort newEnv since attrs->attrs is in sorted order.
 
     for (auto & i : attrs->attrs)
-        i.second.e->bindVars(es, i.second.inherited ? env : newEnv);
+        i.second.e->bindVars(es, i.second.inherited() ? env : newEnv);
 
     if (es.debugRepl)
         es.exprEnvs.insert(std::make_pair(this, newEnv));
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 6f34afaa7..fe75592f0 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -154,13 +154,24 @@ struct ExprAttrs : Expr
     bool recursive;
     PosIdx pos;
     struct AttrDef {
-        bool inherited;
+        enum class Kind {
+            /** `attr = expr;` */
+            Plain,
+            /** `inherit attr1 attrn;` */
+            Inherited,
+            /** `inherit (expr) attr1 attrn;` */
+            InheritedFrom,
+        };
+
+        Kind kind;
         Expr * e;
         PosIdx pos;
         Displacement displ; // displacement
-        AttrDef(Expr * e, const PosIdx & pos, bool inherited=false)
-            : inherited(inherited), e(e), pos(pos) { };
+        AttrDef(Expr * e, const PosIdx & pos, Kind kind = Kind::Plain)
+            : kind(kind), e(e), pos(pos) { };
         AttrDef() { };
+
+        bool inherited() const { return kind == Kind::Inherited; }
     };
     typedef std::map<Symbol, AttrDef> AttrDefs;
     AttrDefs attrs;
diff --git a/src/libexpr/parser-state.hh b/src/libexpr/parser-state.hh
index acadb676d..fa417b0be 100644
--- a/src/libexpr/parser-state.hh
+++ b/src/libexpr/parser-state.hh
@@ -88,7 +88,7 @@ inline void ParserState::addAttr(ExprAttrs * attrs, AttrPath && attrPath, Expr *
         if (i->symbol) {
             ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
             if (j != attrs->attrs.end()) {
-                if (!j->second.inherited) {
+                if (!j->second.inherited()) {
                     ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.e);
                     if (!attrs2) dupAttr(attrPath, pos, j->second.pos);
                     attrs = attrs2;
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 447e4d61a..ae5723a6f 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -311,7 +311,9 @@ binds
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
               state->dupAttr(i.symbol, state->at(@3), $$->attrs[i.symbol].pos);
           auto pos = state->at(@3);
-          $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprVar(CUR_POS, i.symbol), pos, true));
+          $$->attrs.emplace(
+              i.symbol,
+              ExprAttrs::AttrDef(new ExprVar(CUR_POS, i.symbol), pos, ExprAttrs::AttrDef::Kind::Inherited));
       }
       delete $3;
     }
@@ -321,7 +323,12 @@ binds
       for (auto & i : *$6) {
           if ($$->attrs.find(i.symbol) != $$->attrs.end())
               state->dupAttr(i.symbol, state->at(@6), $$->attrs[i.symbol].pos);
-          $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprSelect(CUR_POS, $4, i.symbol), state->at(@6)));
+          $$->attrs.emplace(
+              i.symbol,
+              ExprAttrs::AttrDef(
+                  new ExprSelect(CUR_POS, $4, i.symbol),
+                  state->at(@6),
+                  ExprAttrs::AttrDef::Kind::InheritedFrom));
       }
       delete $6;
     }