Merge pull request #9617 from 9999years/stack-overflow-segfault

Fix segfault on infinite recursion in some cases

(cherry picked from commit bf1b294bd81ca76c5ec9fe3ecd52196bf52a8300)
Change-Id: Id137541426ec8536567835953fccf986a3aebf16

src/libexpr/eval.hh

@@ -629,6 +629,11 @@ private:
         const SourcePath & basePath,
         std::shared_ptr<StaticEnv> & staticEnv);
 
+    /**
+     * Current Nix call stack depth, used with `max-call-depth` setting to throw stack overflow hopefully before we run out of system stack.
+     */
+    size_t callDepth = 0;
+
 public:
 
     /**