find-function-source-directory

[Richard Copley <rcopley@gmail.com>]

I want 'find-function' to go to the .el files in my build directory
"c:/projects/emacs/", not the installed .el.gz files
in "c:/msys64/mingw64/share/emacs/27.0.50/". The docstring for
'find-function' suggests it's possible (but doesn't give an example):

    The library where FUNCTION is defined is searched for in
    ‘find-function-source-path’, if non-nil, otherwise in ‘load-path’.

I tried each of these in my init file, with no effect:

(setq find-function-source-path "c:/projects/emacs/")
(setq find-function-source-path "c:/projects/emacs/lisp/")
(setq find-function-source-path
      (mapcar
       (lambda (x)
         (if (string-match "\\`c:/msys64/mingw64/share/emacs/27.0.50/" x)
             (replace-match "c:/projects/emacs/" nil nil x)
           x))
       load-path))

Did I miss something?