bug#18971: 25.0.50; incorrect warning from byte compiler

bug#18971: 25.0.50; incorrect warning from byte compiler

[Tom Tromey]

Byte compile this file:

; -*- lexical-binding:t -*-
(require 'bytecomp)
(defun z ()
  (byte-compile-close-variables
   (message "hi")))

I get:

In toplevel form:
q.el:3:1:Warning: Unused lexical variable `byte-compile-free-assignments'
q.el:3:1:Warning: Unused lexical variable `byte-compile-free-references'
q.el:3:1:Warning: Unused lexical variable `byte-compile--outbuffer'

I think the warning seems wrong.  bytecomp.el has a defvar for each of
these variables, so I expected them not to be considered lexical.




In GNU Emacs 25.0.50.8 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.9)
 of 2014-11-05 on bapiya
Repository revision: 118301 monnier@iro.umontreal.ca-20141106032723-sooywb316jlfcpd9
Windowing system distributor `Fedora Project', version 11.0.11404000
Configured using:
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C-x C-g is undefined
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Saving file /home/tromey/Emacs/ET/q.el...
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bug#18971: 25.0.50; incorrect warning from byte compiler

[Stefan Monnier]

> ; -*- lexical-binding:t -*-
> (require 'bytecomp)
> (defun z ()
>   (byte-compile-close-variables
>    (message "hi")))

If it hurts, don't do that.

`byte-compile-close-variables' is an internal macro in bytecomp.el.
Why do you need to use it elsewhere?


        Stefan

bug#18971: 25.0.50; incorrect warning from byte compiler

[Tom Tromey]

>>>>> "Stefan" == Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> ; -*- lexical-binding:t -*-
>> (require 'bytecomp)
>> (defun z ()
>> (byte-compile-close-variables
>> (message "hi")))

Stefan> If it hurts, don't do that.

Stefan> `byte-compile-close-variables' is an internal macro in bytecomp.el.
Stefan> Why do you need to use it elsewhere?

I want to be able to call byte-optimize-form and was under the
impression that byte-compile-close-variables was needed.  I'm doing this
for a project I'm working on where it is convenient to let the byte
compiler code macroexpand a form and do some simple optimizations on it.

I guess I don't understand why this would not be a bug, though.
Or at least it perplexes me why this happens; my only theory is that
somehow the defvars aren't seen when byte-compiling my file.  I suppose
if I wanted to export a macro like this, I would need it to come with
special declarations for the variables?  Except I didn't see a way to do
that either.

Tom

bug#18971: 25.0.50; incorrect warning from byte compiler

[Stefan Monnier]

> I want to be able to call byte-optimize-form and was under the
> impression that byte-compile-close-variables was needed.  I'm doing this
> for a project I'm working on where it is convenient to let the byte
> compiler code macroexpand a form and do some simple optimizations on it.

Just curious: why do you need those simple optimizations performed by
byte-optimize-form?

> I guess I don't understand why this would not be a bug, though.
> Or at least it perplexes me why this happens; my only theory is that
> somehow the defvars aren't seen when byte-compiling my file.  I suppose
> if I wanted to export a macro like this, I would need it to come with
> special declarations for the variables?  Except I didn't see a way to do
> that either.

Those vars are not globally bound, i.e. they are only declared with
(defvar <var>) and this only affects the file in which they appear (or
even the scope, in case they appear within a defun body).

So the macro would need to expand to something like

   (progn
     (defvar byte-compile-free-assignments)
     ...
     (defvar byte-compile-free-references)
     (let (...) ...))

if it was meant to be used outside of bytecomp.el.


        Stefan

bug#18971: 25.0.50; incorrect warning from byte compiler

[Tom Tromey]

>> I want to be able to call byte-optimize-form and was under the
>> impression that byte-compile-close-variables was needed.  I'm doing this
>> for a project I'm working on where it is convenient to let the byte
>> compiler code macroexpand a form and do some simple optimizations on it.

Stefan> Just curious: why do you need those simple optimizations performed by
Stefan> byte-optimize-form?

I'm writing an elisp compiler and it just seemed handy.
I can probably reimplement the optimizations though.

Tom

bug#18971: 25.0.50; incorrect warning from byte compiler

[Stefan Monnier]

> I'm writing an elisp compiler and it just seemed handy.
> I can probably reimplement the optimizations though.

Or you can add all the corresponding (defvar <foo>), of course.


        Stefan

bug#18971: 25.0.50; incorrect warning from byte compiler

[Lars Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> I'm writing an elisp compiler and it just seemed handy.
>> I can probably reimplement the optimizations though.
>
> Or you can add all the corresponding (defvar <foo>), of course.

So there doesn't seem to be a bug here, and I'm closing this bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no