Merge pull request #9370 from hercules-ci/add-value-types

refactor: Add `Value` types, use `std::span` for list iteration

src/libexpr/value.hh

@@ -3,6 +3,7 @@
 
 #include <cassert>
 #include <climits>
+#include <span>
 
 #include "symbol-table.hh"
 #include "value/context.hh"
@@ -158,18 +159,13 @@ public:
     inline bool isPrimOp() const { return internalType == tPrimOp; };
     inline bool isPrimOpApp() const { return internalType == tPrimOpApp; };
 
-    union
-    {
-        NixInt integer;
-        bool boolean;
-
     /**
      * Strings in the evaluator carry a so-called `context` which
      * is a list of strings representing store paths.  This is to
      * allow users to write things like
-
+     *
      *   "--with-freetype2-library=" + freetype + "/lib"
-
+     *
      * where `freetype` is a derivation (or a source to be copied
      * to the store).  If we just concatenated the strings without
      * keeping track of the referenced store paths, then if the
@@ -185,15 +181,38 @@ public:
 
      * For canonicity, the store paths should be in sorted order.
      */
-        struct {
+    struct StringWithContext {
         const char * c_str;
         const char * * context; // must be in sorted order
-        } string;
+    };
 
-        struct {
+    struct Path {
         InputAccessor * accessor;
         const char * path;
-        } _path;
+    };
+
+    struct ClosureThunk {
+        Env * env;
+        Expr * expr;
+    };
+
+    struct FunctionApplicationThunk {
+        Value * left, * right;
+    };
+
+    struct Lambda {
+        Env * env;
+        ExprLambda * fun;
+    };
+
+    union
+    {
+        NixInt integer;
+        bool boolean;
+
+        StringWithContext string;
+
+        Path _path;
 
         Bindings * attrs;
         struct {
@@ -201,21 +220,11 @@ public:
             Value * * elems;
         } bigList;
         Value * smallList[2];
-        struct {
+        ClosureThunk thunk;
-            Env * env;
+        FunctionApplicationThunk app;
-            Expr * expr;
+        Lambda lambda;
-        } thunk;
-        struct {
-            Value * left, * right;
-        } app;
-        struct {
-            Env * env;
-            ExprLambda * fun;
-        } lambda;
         PrimOp * primOp;
-        struct {
+        FunctionApplicationThunk primOpApp;
-            Value * left, * right;
-        } primOpApp;
         ExternalValueBase * external;
         NixFloat fpoint;
     };
@@ -387,7 +396,13 @@ public:
         return internalType == tList1 || internalType == tList2 ? smallList : bigList.elems;
     }
 
-    const Value * const * listElems() const
+    std::span<Value * const> listItems() const
+    {
+        assert(isList());
+        return std::span<Value * const>(listElems(), listSize());
+    }
+
+    Value * const * listElems() const
     {
         return internalType == tList1 || internalType == tList2 ? smallList : bigList.elems;
     }
@@ -406,34 +421,6 @@ public:
      */
     bool isTrivial() const;
 
-    auto listItems()
-    {
-        struct ListIterable
-        {
-            typedef Value * const * iterator;
-            iterator _begin, _end;
-            iterator begin() const { return _begin; }
-            iterator end() const { return _end; }
-        };
-        assert(isList());
-        auto begin = listElems();
-        return ListIterable { begin, begin + listSize() };
-    }
-
-    auto listItems() const
-    {
-        struct ConstListIterable
-        {
-            typedef const Value * const * iterator;
-            iterator _begin, _end;
-            iterator begin() const { return _begin; }
-            iterator end() const { return _end; }
-        };
-        assert(isList());
-        auto begin = listElems();
-        return ConstListIterable { begin, begin + listSize() };
-    }
-
     SourcePath path() const
     {
         assert(internalType == tPath);

src/nix-env/nix-env.cc

@@ -172,7 +172,7 @@ static void loadSourceExpr(EvalState & state, const SourcePath & path, Value & v
        directory). */
     else if (st.type == InputAccessor::tDirectory) {
         auto attrs = state.buildBindings(maxAttrs);
-        attrs.alloc("_combineChannels").mkList(0);
+        state.mkList(attrs.alloc("_combineChannels"), 0);
         StringSet seen;
         getAllExprs(state, path, seen, attrs);
         v.mkAttrs(attrs);