fs/scoped: add scoped_dir convenience function

fs/scoped.cpp

@@ -7,6 +7,7 @@
  */
 
 #include "./scoped.hpp"
+#include "./tmp.hpp"
 
 #include <cruft/util/debug/assert.hpp>
 
@@ -90,3 +91,11 @@ scoped_dir::scoped_dir (std::filesystem::path &&_path)
 {
     CHECK (std::filesystem::is_directory (get ()));
 }
+
+
+///////////////////////////////////////////////////////////////////////////////
+cruft::fs::scoped_dir
+cruft::fs::scoped_tmpdir ()
+{
+    return scoped_dir (cruft::fs::mktmpdir ());
+}

fs/scoped.hpp

@@ -50,4 +50,8 @@ namespace cruft::fs {
 
         using scoped_path::scoped_path;
     };
+
+
+    /// A convenience function equivalent to `scoped_dir(maketmpdir())`
+    scoped_dir scoped_tmpdir (void);
 }