Info Catalog elisp: Warnings elisp: Warning Variables

elisp: Warning Basics

 
 37.5.1 Warning Basics
 ---------------------
 
 Every warning has a textual message, which explains the problem for the
 user, and a “severity level” which is a symbol.  Here are the possible
 severity levels, in order of decreasing severity, and their meanings:
 
 ‘:emergency’
      A problem that will seriously impair Emacs operation soon if you do
      not attend to it promptly.
 ‘:error’
      A report of data or circumstances that are inherently wrong.
 ‘:warning’
      A report of data or circumstances that are not inherently wrong,
      but raise suspicion of a possible problem.
 ‘:debug’
      A report of information that may be useful if you are debugging.
 
    When your program encounters invalid input data, it can either signal
 a Lisp error by calling ‘error’ or ‘signal’ or report a warning with
 severity ‘:error’.  Signaling a Lisp error is the easiest thing to do,
 but it means the program cannot continue processing.  If you want to
 take the trouble to implement a way to continue processing despite the
 bad data, then reporting a warning of severity ‘:error’ is the right way
 to inform the user of the problem.  For instance, the Emacs Lisp byte
 compiler can report an error that way and continue compiling other
 functions.  (If the program signals a Lisp error and then handles it
 with ‘condition-case’, the user won’t see the error message; it could
 show the message to the user by reporting it as a warning.)
 
    Each warning has a “warning type” to classify it.  The type is a list
 of symbols.  The first symbol should be the custom group that you use
 for the program’s user options.  For example, byte compiler warnings use
 the warning type ‘(bytecomp)’.  You can also subcategorize the warnings,
 if you wish, by using more symbols in the list.
 
  -- Function: display-warning type message &optional level buffer-name
      This function reports a warning, using MESSAGE as the message and
      TYPE as the warning type.  LEVEL should be the severity level, with
      ‘:warning’ being the default.
 
      BUFFER-NAME, if non-‘nil’, specifies the name of the buffer for
      logging the warning.  By default, it is ‘*Warnings*’.
 
  -- Function: lwarn type level message &rest args
      This function reports a warning using the value of ‘(format-message
      MESSAGE ARGS...)’ as the message in the ‘*Warnings*’ buffer.  In
      other respects it is equivalent to ‘display-warning’.
 
  -- Function: warn message &rest args
      This function reports a warning using the value of ‘(format-message
      MESSAGE ARGS...)’ as the message, ‘(emacs)’ as the type, and
      ‘:warning’ as the severity level.  It exists for compatibility
      only; we recommend not using it, because you should specify a
      specific warning type.
 

Info Catalog elisp: Warnings elisp: Warning Variables