refactor(tvix): add explicit copy/move constructors for Value

This is in preparation for making some of Value's members into refcounted ('smart') pointers.

Change-Id: Ibc54e23ac35766a2fd4e14871c9a7c936a603778
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1743
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

third_party/nix/src/libexpr/CMakeLists.txt

@@ -62,6 +62,7 @@ target_sources(nixexpr
     parser.cc
     primops.cc
     symbol-table.cc
+    value.cc
     value-to-json.cc
     value-to-xml.cc
 )

third_party/nix/src/libexpr/value.cc

@@ -0,0 +1,121 @@
+#include "libexpr/value.hh"
+
+#include <glog/logging.h>
+
+namespace nix {
+
+Value::Value(const Value& copy) { *this = copy; }
+
+Value::Value(Value&& move) { *this = move; }
+
+Value& Value::operator=(const Value& copy) {
+  if (type != copy.type) {
+    memset(this, 0, sizeof(*this));
+  }
+  type = copy.type;
+  switch (type) {
+    case tInt:
+      integer = copy.integer;
+      break;
+    case tBool:
+      boolean = copy.boolean;
+      break;
+    case tString:
+      string = copy.string;
+      break;
+    case tPath:
+      path = copy.path;
+      break;
+    case tNull:
+      /* no fields */
+      break;
+    case tAttrs:
+      attrs = copy.attrs;
+      break;
+    case tList:
+      list = copy.list;
+      break;
+    case tThunk:
+      thunk = copy.thunk;
+      break;
+    case tApp:
+      app = copy.app;
+      break;
+    case tLambda:
+      lambda = copy.lambda;
+      break;
+    case tBlackhole:
+      /* no fields */
+      break;
+    case tPrimOp:
+      primOp = copy.primOp;
+      break;
+    case tPrimOpApp:
+      primOpApp = copy.primOpApp;
+      break;
+    case _reserved1:
+      LOG(FATAL) << "attempted to assign a tExternal value";
+      break;
+    case tFloat:
+      fpoint = copy.fpoint;
+      break;
+  }
+  return *this;
+}
+
+Value& Value::operator=(Value&& move) {
+  if (type != move.type) {
+    memset(this, 0, sizeof(*this));
+  }
+  type = move.type;
+  switch (type) {
+    case tInt:
+      integer = move.integer;
+      break;
+    case tBool:
+      boolean = move.boolean;
+      break;
+    case tString:
+      string = move.string;
+      break;
+    case tPath:
+      path = move.path;
+      break;
+    case tNull:
+      /* no fields */
+      break;
+    case tAttrs:
+      attrs = move.attrs;
+      break;
+    case tList:
+      list = move.list;
+      break;
+    case tThunk:
+      thunk = move.thunk;
+      break;
+    case tApp:
+      app = move.app;
+      break;
+    case tLambda:
+      lambda = move.lambda;
+      break;
+    case tBlackhole:
+      /* no fields */
+      break;
+    case tPrimOp:
+      primOp = move.primOp;
+      break;
+    case tPrimOpApp:
+      primOpApp = move.primOpApp;
+      break;
+    case _reserved1:
+      LOG(FATAL) << "attempted to assign a tExternal value";
+      break;
+    case tFloat:
+      fpoint = move.fpoint;
+      break;
+  }
+  return *this;
+}
+
+}  // namespace nix

third_party/nix/src/libexpr/value.hh

@@ -105,6 +105,13 @@ struct Value {
     NixFloat fpoint;
   };
 
+  Value() : type(tInt), integer(0) {}
+  Value(const Value& copy);
+  Value(Value&& move);
+  ~Value() {}
+  Value& operator=(const Value& copy);
+  Value& operator=(Value&& move);
+
   bool isList() const { return type == tList; }
 
   size_t listSize() const { return list->size(); }