-(declare-function etags-search-path "etags" ())
-
-(defvar project-search-path-function #'etags-search-path
- "Function that returns a list of source root directories.
+;; FIXME: Using the current approach, we don't have access to the
+;; "library roots" of language A from buffers of language B, which
+;; seems desirable in multi-language projects, at least for some
+;; potential uses, like "jump to a file in project or library".
+;;
+;; We can add a second argument to this function: a file extension, or
+;; a language name. Some projects will know the set of languages used
+;; in them; for others, like VC-based projects, we'll need
+;; auto-detection. I see two options:
+;;
+;; - That could be implemented as a separate second hook, with a
+;; list of functions that return file extensions.
+;;
+;; - This variable will be turned into a hook with "append" semantics,
+;; and each function in it will perform auto-detection when passed
+;; nil instead of an actual file extension. Then this hook will, in
+;; general, be modified globally, and not from major mode functions.
+(defvar project-library-roots-function 'etags-library-roots
+ "Function that returns a list of library roots.