compiler doesn't know about (@pxref{Compiler Errors}). Sometimes this
indicates a real problem, but usually the functions in question are
defined in other files which would be loaded if that code is run. For
-example, byte-compiling @file{fortran.el} used to warn:
+example, byte-compiling @file{simple.el} used to warn:
@example
-In end of data:
-fortran.el:2152:1:Warning: the function ‘gud-find-c-expr’ is not
- known to be defined.
+simple.el:8727:1:Warning: the function ‘shell-mode’ is not known to be
+ defined.
@end example
-In fact, @code{gud-find-c-expr} is only used in the function that
-Fortran mode uses for the local value of
-@code{gud-find-expr-function}, which is a callback from GUD; if it is
-called, the GUD functions will be loaded. When you know that such a
-warning does not indicate a real problem, it is good to suppress the
-warning. That makes new warnings which might mean real problems more
-visible. You do that with @code{declare-function}.
+In fact, @code{shell-mode} is used only in a function that executes
+@code{(require 'shell)} before calling @code{shell-mode}, so
+@code{shell-mode} will be defined properly at run-time. When you know
+that such a warning does not indicate a real problem, it is good to
+suppress the warning. That makes new warnings which might mean real
+problems more visible. You do that with @code{declare-function}.
All you need to do is add a @code{declare-function} statement before the
first use of the function in question:
@example
-(declare-function gud-find-c-expr "gud.el" nil)
+(declare-function shell-mode "shell" ())
@end example
-This says that @code{gud-find-c-expr} is defined in @file{gud.el} (the
+This says that @code{shell-mode} is defined in @file{shell.el} (the
@samp{.el} can be omitted). The compiler takes for granted that that file
really defines the function, and does not check.
The optional third argument specifies the argument list of
-@code{gud-find-c-expr}. In this case, it takes no arguments
+@code{shell-mode}. In this case, it takes no arguments
(@code{nil} is different from not specifying a value). In other
cases, this might be something like @code{(file &optional overwrite)}.
You don't have to specify the argument list, but if you do the
byte compiler can check that the calls match the declaration.
-@defmac declare-function function file &optional arglist fileonly
-Tell the byte compiler to assume that @var{function} is defined, with
-arguments @var{arglist}, and that the definition should come from the
-file @var{file}. @var{fileonly} non-@code{nil} means only check that
+@defmac declare-function function file &rest args
+Tell the byte compiler to assume that @var{function} is defined in the
+file @var{file}. The trailing arguments @var{args} can contain one or
+two optional arguments. The first optional argument @var{arglist} is
+either @code{t}, meaning the argument list is unspecified, or a list
+of formal parameters in the same style as @code{defun}.@footnote{An
+omitted @var{arglist} defaults to @code{t}, not @code{nil}; this
+atypical behavior is why @code{declare-function} is defined to have
+the formal parameters @code{(function file &rest args)}, not
+@code{(function file &optional arglist fileonly)}.} The second
+optional argument @var{fileonly} non-@code{nil} means only check that
@var{file} exists, not that it actually defines @var{function}.
@end defmac