Introduce AttrPath type

This is basically an alias for std::vector<Symbol>.

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/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/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());