Science to suppress compiler warnings

[Xavier Maillard]

Hi,

Elisp manual at "Compiler Errors" section (16.6) says we should
conditionalize variable use with a boundp test (same thing for
undefined function) but I find it very unpractical.

I thought (probably was wrong) that:

(eval-when-compile (defvar foo nil))

would do the trick. Is it the correct way to avoid warnings ?

Also while at it, here is what I got when compiling an old
package:

records.el:931:49:Warning: reference to free variable
`records-link-menu-map'

In records-mode:
records.el:1066:23:Warning: assignment to free variable
    `records-link-menu-map'

What is the difference between these two warnings exactly ?
Adding a defvar at the right place fixed that but to feed my
curiosity.

Regards,

Xavier