Re: Bug in emacs

[era@iki.fi]

On Mon, 13 Oct 2003 10:28:06 -0600, Kevin Rodgers <ihs_4664@yahoo.com>
posted to gmane.emacs.bugs:
 > era@iki.fi wrote:
 >> I'm not sure what the bug really is. Perhaps it would be useful to
 >> get a warning when compiling / evaling something when a macro +is+
 >> in effect and the file you are compiling is not pulling it in
 >> properly? Then at least you get a hint to fix it while you still
 >> can, while those who do it right will not experience any adverse
 >> effects.
 > When the compiler comes across a (function arg ...) form, either the
 > function is defined or it isn't.  If it's defined, either as a function
 > or a macro, all is well.  If it's not defined, the compiler can't know
 > whether it is a function or a macro and assumes it's a function.  A
 > macro can't be "in effect" if it's file was not loaded "properly".

What I'm saying is that macro expansion during compilation could
trigger a warning if the macro is not loaded properly by the code
which is being compiled. This is a fuzzy idea at best, but I was
thinking of something like:

  0. Maintain a buffer of per-byte-compilation macros

  1. When a new byte compilation starts, flush the buffer of macros.
     Set a flag to indicate that byte compilation is in progress. (I
     would kind of assume that this already happens but I haven't
     checked.)

  2. When byte compilation is taking place and a macro is defined, add
     the macro to the buffer of per-byte-compilation macros with the
     property "defined during compilation".

  3. When byte compilation is taking place and a macro is expanded,
     check in the buffer, and if the macro is not listed as having
     been defined during this compilation, throw a warning.

  4. When byte compilation finishes, the flag to indicate that byte
     compilation is taking place will need to be taken down, of
     course.

This obviously requires already-loaded requires etc to be performed
anew during byte compilation, or some cunning caching of the buffer
which keeps track of when and where a macro was defined (maybe make it
global and permanent per session instead of per-compilation?)

 > The compiler does issue warnings when it encounters an undefined
 > macro/function:
 > While compiling the end of the data in file /home/kevinr/emacs/foo.el:
 >    ** the function bar is not known to be defined.

So now you'd also get something like

  While compiling toplevel forms:
    ** reference to macro `foo' which was not defined during compilation

as a warning that the code may not execute correctly on a system where
the macro is not somehow automatically loaded before the compiled code
will be executed. (As a bonus maybe the `foo' could be clickable so
you could look at the macro's documentation and maybe find out where
it is defined.)

/* era */

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