byte-compile-warnings is a variable defined in `bytecomp.el'.
Its value is

  • This variable is safe as a file local variable if its value
    satisfies the predicate which is a byte-compiled expression.

List of warnings that the byte-compiler should issue (t for all).

Elements of the list may be:

free-vars references to variables not in the current lexical scope.
unresolved calls to unknown functions.
callargs function calls with args that don't match the definition.
redefine function name redefined from a macro to ordinary function or vice
versa, or redefined to take a different number of arguments.
obsolete obsolete variables and functions.
noruntime functions that may not be defined at runtime (typically
defined only under `eval-when-compile').
cl-functions calls to runtime functions (as distinguished from macros and
aliases) from the old CL package (not the newer cl-lib).
commands that normally shouldn't be called from Lisp code.
lexical global/dynamic variables lacking a prefix.
make-local calls to make-variable-buffer-local that may be incorrect.
mapcar mapcar called for effect.
constants let-binding of, or assignment to, constants/nonvariables.
suspicious constructs that usually don't do what the coder wanted.

If the list begins with `not', then the remaining elements specify warnings to
suppress. For example, (not mapcar) will suppress warnings about mapcar.

You can customize this variable.