GNU bug report logs - #4845
23.1.50; Uninterned symbols in .elc files

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Message #5 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Helmut Eller <eller.helmut <at> gmail.com>
To: emacs-pretest-bug <at> gnu.org
Subject: 23.1.50; Uninterned symbols in .elc files
Date: Sun, 01 Nov 2009 09:25:32 +0100

In GNU Emacs 23.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.12.11)
loading a file x.el with contents

 (defmacro foo ()
   (let ((sym (make-symbol "bar")))
     `(progn
        (defun ,sym () (message "function %s called" ',sym))
        (,sym))))
 
 (foo)

works as expected:

 shell> emacs -Q -batch -load x.el
 function bar called

However loading the corresponding compiled file signals an error:

 shell> emacs -Q -batch -eval '(byte-compile-file "x.el")' -load x.elc
 Wrote /tmp/x.elc
 Symbol's function definition is void: bar
 [Exit 255]

There is a #1=#:bar in the constant pool of the compiled function but #1
isn't used at the call site.

Helmut

Message #8 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: Marcin Borkowski <mbork <at> amu.edu.pl>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 4845 <at> debbugs.gnu.org
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: Sun, 17 Jan 2016 22:12:57 +0100

Hi,

this message is just to mention that this bug seems to persist in GNU
Emacs 25.1.50.1.

Best,
mb


On 2009-11-01, at 09:25, Helmut Eller <eller.helmut <at> gmail.com> wrote:

> In GNU Emacs 23.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.12.11)
> loading a file x.el with contents
>
>  (defmacro foo ()
>    (let ((sym (make-symbol "bar")))
>      `(progn
>         (defun ,sym () (message "function %s called" ',sym))
>         (,sym))))
>  
>  (foo)
>
> works as expected:
>
>  shell> emacs -Q -batch -load x.el
>  function bar called
>
> However loading the corresponding compiled file signals an error:
>
>  shell> emacs -Q -batch -eval '(byte-compile-file "x.el")' -load x.elc
>  Wrote /tmp/x.elc
>  Symbol's function definition is void: bar
>  [Exit 255]
>
> There is a #1=#:bar in the constant pool of the compiled function but #1
> isn't used at the call site.
>
> Helmut

Message #11 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Marcin Borkowski <mbork <at> amu.edu.pl>
Cc: 4845 <at> debbugs.gnu.org, Helmut Eller <eller.helmut <at> gmail.com>
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: 19 Jan 2016 12:39:56 -0000

Hello, Marcin and Helmut.

In article <mailman.2481.1453074610.843.bug-gnu-emacs <at> gnu.org> you wrote:
> Hi,

> this message is just to mention that this bug seems to persist in GNU
> Emacs 25.1.50.1.

I'm convinced this is not a bug, though I could be wrong.

> Best,
> mb


> On 2009-11-01, at 09:25, Helmut Eller <eller.helmut <at> gmail.com> wrote:

>> In GNU Emacs 23.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.12.11)
>> loading a file x.el with contents

>>  (defmacro foo ()
>>    (let ((sym (make-symbol "bar")))
>>      `(progn
>>         (defun ,sym () (message "function %s called" ',sym))
>>         (,sym))))
>>
>>  (foo)

>> works as expected:

>>  shell> emacs -Q -batch -load x.el
>>  function bar called

>> However loading the corresponding compiled file signals an error:

>>  shell> emacs -Q -batch -eval '(byte-compile-file "x.el")' -load x.elc
>>  Wrote /tmp/x.elc
>>  Symbol's function definition is void: bar
>>  [Exit 255]

For reference, here are the contents of the compiled .elc file:

(defalias 'foo '(macro . #[nil "\301\302!^X\303\304^H\305\306\307\310^HDEF^HCE)\207" [sym make-symbol "bar" progn defun nil message "function %s called" quote] 8]))
(defalias 'bar #[nil "\300\301\302\"\207" [message "function %s called" #1=#:bar] 3])
(#:bar)

Important to note is that "(foo)" is expanded at byte compile time, not
at load time.  The uninterned symbol "bar" is created at compile time
during the expansion of "(foo)", but is not stored in the .elc file
anywhere.  That symbol thus exists only during the compilation of form
"(foo)" - at loading time it no longer exists.

Thus, trying to call "(#:bar)" at load time is doomed to fail.  (Though I
don't fully understand what "#:bar" means.)

There may be a bug in the compiler, in that it compiles a function
definition for the normal symbol 'bar rather than giving an error
message.

To fix the macro `foo', generate code to create the uninterned symbol at
run time rather than at compile time.  Maybe.

>> There is a #1=#:bar in the constant pool of the compiled function but #1
>> isn't used at the call site.

>> Helmut

-- 
Alan Mackenzie (Nuremberg, Germany).

Message #14 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: John Wiegley <jwiegley <at> gmail.com>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Marcin Borkowski <mbork <at> amu.edu.pl>, 4845 <at> debbugs.gnu.org,
 Helmut Eller <eller.helmut <at> gmail.com>
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: Tue, 19 Jan 2016 09:26:14 -0800

[Message part 1 (text/plain, inline)]

>>>>> Alan Mackenzie <acm <at> muc.de> writes:

>>> (defmacro foo ()
>>> (let ((sym (make-symbol "bar")))
>>> `(progn
>>> (defun ,sym () (message "function %s called" ',sym))
>>> (,sym))))
>>> 
>>> (foo)

>>> However loading the corresponding compiled file signals an error:

shell> emacs -Q -batch -eval '(byte-compile-file "x.el")' -load x.elc
>>> Wrote /tmp/x.elc
>>> Symbol's function definition is void: bar

This example becomes clearer if we use `gensym' instead of `make-symbol
"bar"`.  Here is a macro expansion:

Byte-compiled:

  (progn
    (defun bar68503 nil
      (message "function %s called" '#:bar68503))
    (#:bar68503))

Interpreted:

  (progn
    (defun bar68503 nil
      (message "function %s called" 'bar68503))
    (bar68503))

What's happening here is this:

  1. At compile-time, we're creating a new, uninterned symbol, and we are
     both passing that symbol to defun, and calling it.

  2. `defun', at compilation time, is using the _name_ of that symbol to
     define a function definition for an interned symbol of the same name.

  3. We then try to print and call the uninterned symbol directly. So what we
     are calling, and what defun defined, are not the same symbol.

This works when non-byte-compiled because we don't inline the symbol
reference, making it a reference by name instead of by value. You can trigger
the same error behavior at interpretation time with:

  (defmacro foo ()
    (let ((sym (gensym)))
      `(progn
         (defun ,sym () (message "function %s called" ',sym))
         (funcall (symbol-function (quote ,sym))))))
  
  (foo)

I don't think this is a bug, rather macro expansion doing exactly what it was
told to do. If anything, it's odd that when interpreting, we expand to a
reference by name; but I suppose that makes sense too, given the more dynamic
nature of interpreted code.

The general rule to follow is: Don't leak internal symbols. If you use
`gensym' or `make-symbol', ensure that all dependencies on that symbol occur
entirely within the macro body. `defun' is used to establish global
definitions, so it effectively "exports" the internal symbol, breaking the
abstraction. That it has inconsistent behavior here is due to differences in
the way that byte-compilation inlines references.

I recommend closure of this bug as expected behavior, unless there are further
concerns.

-- 
John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2

[signature.asc (application/pgp-signature, inline)]

Message #17 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: John Wiegley <jwiegley <at> gmail.com>
Cc: Alan Mackenzie <acm <at> muc.de>, Marcin Borkowski <mbork <at> amu.edu.pl>,
 John Wiegley <johnw <at> gnu.org>, Helmut Eller <eller.helmut <at> gmail.com>,
 4845 <at> debbugs.gnu.org
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: Tue, 19 Jan 2016 20:15:25 +0100

John Wiegley <jwiegley <at> gmail.com> writes:

>   3. We then try to print and call the uninterned symbol directly. So what we
>      are calling, and what defun defined, are not the same symbol.

But theoretically, the byte compiler could do it correctly.

This is how the compiled code looks like currently:

(defalias '#1=#:bar #[0 "[bytes...]" [message "function %s called" #1#] 3])
(#:bar)

If the second line would be

(#1#)

(as the compiler already correctly prints in the function body)

the thing would work AFAIU.  I guess it doesn't because it is a
different expression printed separately.

> I recommend closure of this bug as expected behavior,

I think it's quite unexpected, unless you know about how byte
compilation to files works, and even then...

> unless there are further concerns.

I think this is quite a limitation worth to be fixed, if it is possible
with little effort.

If not, we should at least make the compiler raise an error when it
generates function calls like

    (#:bar)

something like that is not very useful, in no situation.


Michael.

Message #20 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: Helmut Eller <eller.helmut <at> gmail.com>
To: John Wiegley <jwiegley <at> gmail.com>
Cc: Alan Mackenzie <acm <at> muc.de>, Marcin Borkowski <mbork <at> amu.edu.pl>,
 John Wiegley <johnw <at> gnu.org>, 4845 <at> debbugs.gnu.org
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: Tue, 19 Jan 2016 20:44:29 +0100

On Tue, Jan 19 2016, John Wiegley wrote:

> I don't think this is a bug, rather macro expansion doing exactly what it was
> told to do.
 
Interpreted and compiled code behave differently.  That's always a
problem.  Obviously not a big problem.

> The general rule to follow is: Don't leak internal symbols.

I would say "Don't leak non-interned symbols", except that "leaking" is
not a well defined term.

Or alternatively "Keep in mind that uninterned symbols are freshly
created when loading compiled code from files and shared only in certain
situations e.g. for two occurrences inside the same lambda."

The best solution would be to have one constant pool per
compilation-unit instead of a constant pool per function.  But I doubt
that anybody cares enough to implement that.

Helmut

Message #23 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: John Wiegley <jwiegley <at> gmail.com>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: Alan Mackenzie <acm <at> muc.de>, Marcin Borkowski <mbork <at> amu.edu.pl>,
 4845 <at> debbugs.gnu.org
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: Tue, 19 Jan 2016 12:16:57 -0800

[Message part 1 (text/plain, inline)]

>>>>> Helmut Eller <eller.helmut <at> gmail.com> writes:

> Interpreted and compiled code behave differently. That's always a problem.
> Obviously not a big problem.

The number of ways to coax varying behavior from the two execution modes is
legion. I had to bend over backwards to achieve consistency for use-package
when byte-compiling an init.el file versus loading it un-byte-compiled. So I
don't feel this bug is very urgent.

>>>>> Michael Heerdegen <michael_heerdegen <at> web.de> writes:

> I think this is quite a limitation worth to be fixed, if it is possible with
> little effort.

Honestly, we have better things to do. If you still think this is a bug, I'm
fine leaving it open until the day when someone wants to champion the cause of
interpreted/compiled equivalence, but until then, I'd rather focus on other
things.

-- 
John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2

[signature.asc (application/pgp-signature, inline)]

Message #26 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: John Wiegley <jwiegley <at> gmail.com>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: Alan Mackenzie <acm <at> muc.de>, Marcin Borkowski <mbork <at> amu.edu.pl>,
 4845 <at> debbugs.gnu.org, Helmut Eller <eller.helmut <at> gmail.com>
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: Fri, 19 Feb 2016 22:23:41 -0800

>>>>> Michael Heerdegen <michael_heerdegen <at> web.de> writes:

> I think this is quite a limitation worth to be fixed, if it is possible with
> little effort.

If it's possible with little effort, and someone wants to do it, I agree; but
there is no hurry for this one.

-- 
John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2

Message #29 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: John Wiegley <jwiegley <at> gmail.com>, John Wiegley <johnw <at> gnu.org>,
 Helmut Eller <eller.helmut <at> gmail.com>, Marcin Borkowski <mbork <at> amu.edu.pl>,
 Alan Mackenzie <acm <at> muc.de>, 4845 <at> debbugs.gnu.org
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: Sat, 20 Feb 2016 11:01:19 +0100

Michael Heerdegen <michael_heerdegen <at> web.de> writes:

> This is how the compiled code looks like currently:
>
> (defalias '#1=#:bar #[0 "[bytes...]" [message "function %s called" #1#] 3])
> (#:bar)
>
> If the second line would be
>
> (#1#)
>
> (as the compiler already correctly prints in the function body)
>
> the thing would work AFAIU.

It only works inside the same sexp.

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Message #32 received at 4845 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefan <at> marxist.se>
To: John Wiegley <jwiegley <at> gmail.com>
Cc: Alan Mackenzie <acm <at> muc.de>, Marcin Borkowski <mbork <at> amu.edu.pl>,
 John Wiegley <johnw <at> gnu.org>, Helmut Eller <eller.helmut <at> gmail.com>,
 4845 <at> debbugs.gnu.org
Subject: Re: bug#4845: 23.1.50; Uninterned symbols in .elc files
Date: Wed, 18 Nov 2020 18:41:38 -0800

tags wontfix
close 4845
thanks

John Wiegley <jwiegley <at> gmail.com> writes:

>>>>>> Helmut Eller <eller.helmut <at> gmail.com> writes:
>
>> Interpreted and compiled code behave differently. That's always a problem.
>> Obviously not a big problem.
>
> The number of ways to coax varying behavior from the two execution modes is
> legion. I had to bend over backwards to achieve consistency for use-package
> when byte-compiling an init.el file versus loading it un-byte-compiled. So I
> don't feel this bug is very urgent.
>
>>>>>> Michael Heerdegen <michael_heerdegen <at> web.de> writes:
>
>> I think this is quite a limitation worth to be fixed, if it is possible with
>> little effort.
>
> Honestly, we have better things to do. If you still think this is a bug, I'm
> fine leaving it open until the day when someone wants to champion the cause of
> interpreted/compiled equivalence, but until then, I'd rather focus on other
> things.

I tend to agree with John here; it doesn't seem worth spending time on
this.  There also have been no further interest in this bug report
within 4 years.

I'm therefore closing this bug report as wontfix.  If anyone disagrees
with that, feel free to reopen.

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