Introduce AttrPath type

src/libcmd/installable-flake.cc

@@ -171,7 +171,7 @@ std::vector<ref<eval_cache::AttrCursor>> InstallableFlake::getCursors(EvalState
     for (auto & attrPath : attrPaths) {
         debug("trying flake output attribute '%s'", attrPath);
 
-        auto attr = root->findAlongAttrPath(parseAttrPath(state, attrPath));
+        auto attr = root->findAlongAttrPath(AttrPath::parse(state, attrPath));
         if (attr) {
             res.push_back(ref(*attr));
         } else {

src/libcmd/installables.cc

@@ -355,9 +355,9 @@ void completeFlakeRefWithFragment(
             attrPathPrefixes.push_back("");
 
             for (auto & attrPathPrefixS : attrPathPrefixes) {
-                auto attrPathPrefix = parseAttrPath(*evalState, attrPathPrefixS);
+                auto attrPathPrefix = AttrPath::parse(*evalState, attrPathPrefixS);
                 auto attrPathS = attrPathPrefixS + std::string(fragment);
-                auto attrPath = parseAttrPath(*evalState, attrPathS);
+                auto attrPath = AttrPath::parse(*evalState, attrPathS);
 
                 std::string lastAttr;
                 if (!attrPath.empty() && !hasSuffix(attrPathS, ".")) {
@@ -375,9 +375,7 @@ void completeFlakeRefWithFragment(
                         /* Strip the attrpath prefix. */
                         attrPath2.erase(attrPath2.begin(), attrPath2.begin() + attrPathPrefix.size());
                         // FIXME: handle names with dots
-                        completions.add(
-                            flakeRefS + "#" + prefixRoot
-                            + concatStringsSep(".", evalState->symbols.resolve(attrPath2)));
+                        completions.add(flakeRefS + "#" + prefixRoot + attrPath2.to_string(*evalState));
                     }
                 }
             }
@@ -386,7 +384,7 @@ void completeFlakeRefWithFragment(
                attrpaths. */
             if (fragment.empty()) {
                 for (auto & attrPath : defaultFlakeAttrPaths) {
-                    auto attr = root->findAlongAttrPath(parseAttrPath(*evalState, attrPath));
+                    auto attr = root->findAlongAttrPath(AttrPath::parse(*evalState, attrPath));
                     if (!attr)
                         continue;
                     completions.add(flakeRefS + "#" + prefixRoot);

src/libexpr/attr-path.cc

@@ -1,5 +1,6 @@
 #include "nix/expr/attr-path.hh"
 #include "nix/expr/eval-inline.hh"
+#include "nix/util/strings-inline.hh"
 
 namespace nix {
 
@@ -30,14 +31,24 @@ static Strings parseAttrPath(std::string_view s)
     return res;
 }
 
-std::vector<Symbol> parseAttrPath(EvalState & state, std::string_view s)
+AttrPath AttrPath::parse(EvalState & state, std::string_view s)
 {
-    std::vector<Symbol> res;
+    AttrPath res;
     for (auto & a : parseAttrPath(s))
         res.push_back(state.symbols.create(a));
     return res;
 }
 
+std::string AttrPath::to_string(EvalState & state) const
+{
+    return dropEmptyInitThenConcatStringsSep(".", state.symbols.resolve({*this}));
+}
+
+std::vector<SymbolStr> AttrPath::resolve(EvalState & state) const
+{
+    return state.symbols.resolve({*this});
+}
+
 std::pair<Value *, PosIdx>
 findAlongAttrPath(EvalState & state, const std::string & attrPath, Bindings & autoArgs, Value & vIn)
 {

src/libexpr/eval-cache.cc

@@ -364,7 +364,7 @@ void AttrCursor::fetchCachedValue()
         throw CachedEvalError(parent->first, parent->second);
 }
 
-std::vector<Symbol> AttrCursor::getAttrPath() const
+AttrPath AttrCursor::getAttrPath() const
 {
     if (parent) {
         auto attrPath = parent->first->getAttrPath();
@@ -374,7 +374,7 @@ std::vector<Symbol> AttrCursor::getAttrPath() const
         return {};
 }
 
-std::vector<Symbol> AttrCursor::getAttrPath(Symbol name) const
+AttrPath AttrCursor::getAttrPath(Symbol name) const
 {
     auto attrPath = getAttrPath();
     attrPath.push_back(name);
@@ -383,12 +383,12 @@ std::vector<Symbol> AttrCursor::getAttrPath(Symbol name) const
 
 std::string AttrCursor::getAttrPathStr() const
 {
-    return dropEmptyInitThenConcatStringsSep(".", root->state.symbols.resolve(getAttrPath()));
+    return getAttrPath().to_string(root->state);
 }
 
 std::string AttrCursor::getAttrPathStr(Symbol name) const
 {
-    return dropEmptyInitThenConcatStringsSep(".", root->state.symbols.resolve(getAttrPath(name)));
+    return getAttrPath(name).to_string(root->state);
 }
 
 Value & AttrCursor::forceValue()
@@ -511,7 +511,7 @@ ref<AttrCursor> AttrCursor::getAttr(std::string_view name)
     return getAttr(root->state.symbols.create(name));
 }
 
-OrSuggestions<ref<AttrCursor>> AttrCursor::findAlongAttrPath(const std::vector<Symbol> & attrPath)
+OrSuggestions<ref<AttrCursor>> AttrCursor::findAlongAttrPath(const AttrPath & attrPath)
 {
     auto res = shared_from_this();
     for (auto & attr : attrPath) {

src/libexpr/eval.cc

@@ -1368,7 +1368,7 @@ void ExprVar::eval(EvalState & state, Env & env, Value & v)
     v = *v2;
 }
 
-static std::string showAttrPath(EvalState & state, Env & env, std::span<const AttrName> attrPath)
+static std::string showAttrSelectionPath(EvalState & state, Env & env, std::span<const AttrName> attrPath)
 {
     std::ostringstream out;
     bool first = true;
@@ -1404,7 +1404,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                                          env,
                                          getPos(),
                                          "while evaluating the attribute '%1%'",
-                                         showAttrPath(state, env, getAttrPath()))
+                                         showAttrSelectionPath(state, env, getAttrPath()))
                                    : nullptr;
 
         for (auto & i : getAttrPath()) {
@@ -1445,7 +1445,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
             auto origin = std::get_if<SourcePath>(&pos2r.origin);
             if (!(origin && *origin == state.derivationInternal))
                 state.addErrorTrace(
-                    e, pos2, "while evaluating the attribute '%1%'", showAttrPath(state, env, getAttrPath()));
+                    e, pos2, "while evaluating the attribute '%1%'", showAttrSelectionPath(state, env, getAttrPath()));
         }
         throw;
     }

src/libexpr/include/nix/expr/attr-path.hh

@@ -19,6 +19,15 @@ findAlongAttrPath(EvalState & state, const std::string & attrPath, Bindings & au
  */
 std::pair<SourcePath, uint32_t> findPackageFilename(EvalState & state, Value & v, std::string what);
 
-std::vector<Symbol> parseAttrPath(EvalState & state, std::string_view s);
+struct AttrPath : std::vector<Symbol>
+{
+    using std::vector<Symbol>::vector;
+
+    static AttrPath parse(EvalState & state, std::string_view s);
+
+    std::string to_string(EvalState & state) const;
+
+    std::vector<SymbolStr> resolve(EvalState & state) const;
+};
 
 } // namespace nix

src/libexpr/include/nix/expr/eval-cache.hh

@@ -4,6 +4,7 @@
 #include "nix/util/sync.hh"
 #include "nix/util/hash.hh"
 #include "nix/expr/eval.hh"
+#include "nix/expr/attr-path.hh"
 
 #include <functional>
 #include <variant>
@@ -124,9 +125,9 @@ public:
         Value * value = nullptr,
         std::optional<std::pair<AttrId, AttrValue>> && cachedValue = {});
 
-    std::vector<Symbol> getAttrPath() const;
+    AttrPath getAttrPath() const;
 
-    std::vector<Symbol> getAttrPath(Symbol name) const;
+    AttrPath getAttrPath(Symbol name) const;
 
     std::string getAttrPathStr() const;
 
@@ -146,7 +147,7 @@ public:
      * 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);
+    OrSuggestions<ref<AttrCursor>> findAlongAttrPath(const AttrPath & attrPath);
 
     std::string getString();
 

src/libexpr/include/nix/expr/nixexpr.hh

@@ -87,9 +87,9 @@ struct AttrName
 
 static_assert(std::is_trivially_copy_constructible_v<AttrName>);
 
-typedef std::vector<AttrName> AttrPath;
+typedef std::vector<AttrName> AttrSelectionPath;
 
-std::string showAttrPath(const SymbolTable & symbols, std::span<const AttrName> attrPath);
+std::string showAttrSelectionPath(const SymbolTable & symbols, std::span<const AttrName> attrPath);
 
 using UpdateQueue = SmallTemporaryValueVector<conservativeStackReservation>;
 

src/libexpr/include/nix/expr/parser-state.hh

@@ -163,20 +163,25 @@ struct ParserState
     static constexpr Expr::AstSymbols s = StaticEvalSymbols::create().exprSymbols;
     const EvalSettings & settings;
 
-    void dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos);
+    void dupAttr(const AttrSelectionPath & attrPath, const PosIdx pos, const PosIdx prevPos);
     void dupAttr(Symbol attr, const PosIdx pos, const PosIdx prevPos);
     void addAttr(
-        ExprAttrs * attrs, AttrPath && attrPath, const ParserLocation & loc, Expr * e, const ParserLocation & exprLoc);
-    void addAttr(ExprAttrs * attrs, AttrPath & attrPath, const Symbol & symbol, ExprAttrs::AttrDef && def);
+        ExprAttrs * attrs,
+        AttrSelectionPath && attrPath,
+        const ParserLocation & loc,
+        Expr * e,
+        const ParserLocation & exprLoc);
+    void addAttr(ExprAttrs * attrs, AttrSelectionPath & attrPath, const Symbol & symbol, ExprAttrs::AttrDef && def);
     void validateFormals(FormalsBuilder & formals, PosIdx pos = noPos, Symbol arg = {});
     Expr * stripIndentation(const PosIdx pos, std::span<std::pair<PosIdx, std::variant<Expr *, StringToken>>> es);
     PosIdx at(const ParserLocation & loc);
 };
 
-inline void ParserState::dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos)
+inline void ParserState::dupAttr(const AttrSelectionPath & attrPath, const PosIdx pos, const PosIdx prevPos)
 {
     throw ParseError(
-        {.msg = HintFmt("attribute '%1%' already defined at %2%", showAttrPath(symbols, attrPath), positions[prevPos]),
+        {.msg = HintFmt(
+             "attribute '%1%' already defined at %2%", showAttrSelectionPath(symbols, attrPath), positions[prevPos]),
          .pos = positions[pos]});
 }
 
@@ -188,9 +193,13 @@ inline void ParserState::dupAttr(Symbol attr, const PosIdx pos, const PosIdx pre
 }
 
 inline void ParserState::addAttr(
-    ExprAttrs * attrs, AttrPath && attrPath, const ParserLocation & loc, Expr * e, const ParserLocation & exprLoc)
+    ExprAttrs * attrs,
+    AttrSelectionPath && attrPath,
+    const ParserLocation & loc,
+    Expr * e,
+    const ParserLocation & exprLoc)
 {
-    AttrPath::iterator i;
+    AttrSelectionPath::iterator i;
     // All attrpaths have at least one attr
     assert(!attrPath.empty());
     auto pos = at(loc);
@@ -236,7 +245,7 @@ inline void ParserState::addAttr(
  * symbol as its last element.
  */
 inline void
-ParserState::addAttr(ExprAttrs * attrs, AttrPath & attrPath, const Symbol & symbol, ExprAttrs::AttrDef && def)
+ParserState::addAttr(ExprAttrs * attrs, AttrSelectionPath & attrPath, const Symbol & symbol, ExprAttrs::AttrDef && def)
 {
     ExprAttrs::AttrDefs::iterator j = attrs->attrs->find(symbol);
     if (j != attrs->attrs->end()) {

src/libexpr/include/nix/expr/symbol-table.hh

@@ -290,7 +290,7 @@ public:
         return Symbol(*symbols.insert(SymbolStr::Key{store, s, buffer}).first);
     }
 
-    std::vector<SymbolStr> resolve(const std::vector<Symbol> & symbols) const
+    std::vector<SymbolStr> resolve(const std::span<const Symbol> & symbols) const
     {
         std::vector<SymbolStr> result;
         result.reserve(symbols.size());

src/libexpr/nixexpr.cc

@@ -57,7 +57,7 @@ void ExprSelect::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "(";
     e->show(symbols, str);
-    str << ")." << showAttrPath(symbols, getAttrPath());
+    str << ")." << showAttrSelectionPath(symbols, getAttrPath());
     if (def) {
         str << " or (";
         def->show(symbols, str);
@@ -69,7 +69,7 @@ void ExprOpHasAttr::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "((";
     e->show(symbols, str);
-    str << ") ? " << showAttrPath(symbols, attrPath) << ")";
+    str << ") ? " << showAttrSelectionPath(symbols, attrPath) << ")";
 }
 
 void ExprAttrs::showBindings(const SymbolTable & symbols, std::ostream & str) const
@@ -261,7 +261,7 @@ void ExprPos::show(const SymbolTable & symbols, std::ostream & str) const
     str << "__curPos";
 }
 
-std::string showAttrPath(const SymbolTable & symbols, std::span<const AttrName> attrPath)
+std::string showAttrSelectionPath(const SymbolTable & symbols, std::span<const AttrName> attrPath)
 {
     std::ostringstream out;
     bool first = true;