`library` also knows its base dir

src/dds/library.cpp

 library library::from_directory(path_ref lib_dir, std::string_view name) {
     auto [sources, inc_dir, src_dir] = collect_pf_sources(lib_dir);
 
-    auto lib = library(name, std::move(sources));;
+    auto lib = library(lib_dir, name, std::move(sources));
 
     if (fs::exists(inc_dir)) {
         lib._pub_inc_dir = inc_dir;
             lib._priv_inc_dir = src_dir;
         }
     } else {
-        lib._pub_inc_dir = src_dir;
+        lib._pub_inc_dir  = src_dir;
         lib._priv_inc_dir = src_dir;
     }
 

src/dds/library.hpp

 };
 
 class library {
+    fs::path    _base_dir;
     std::string _name;
     source_list _sources;
     fs::path    _pub_inc_dir;
     fs::path    _priv_inc_dir;
 
-    library(std::string_view name, source_list&& src)
-        : _name(name)
+    library(path_ref dir, std::string_view name, source_list&& src)
+        : _base_dir(dir)
+        , _name(name)
         , _sources(std::move(src)) {}
 
 public:
         return from_directory(path, path.filename().string());
     }
 
+    path_ref base_dir() const noexcept { return _base_dir; }
     path_ref public_include_dir() const noexcept { return _pub_inc_dir; }
     path_ref private_include_dir() const noexcept { return _priv_inc_dir; }