GNU bug report logs - #36079
Source location information missing from identifiers

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Robert Vollmert <rob <at> vllmrt.net>
To: guile-bugs <at> gnu.org
Subject: unhelpful error message
Date: Mon, 3 Jun 2019 22:42:09 +0200

Working on Guix, I encountered the following:

Within a guix checkout, I edited gnu/packages/haskell.scm, accidentally
making a Haskell comment:

    (arguments
     `(#:tests? #f)) -- sporadic failure: https://github.com/fpco/streaming-commons/issues/49

Then I tried to keep working on my in-development package, and was able to trace
the `guix build` error back to the following:

$ ./pre-inst-env guild compile ../modules/postgrest.scm
;;; note: source file /home/rob/guix/gnu/packages/haskell.scm
;;;       newer than compiled /home/rob/guix/gnu/packages/haskell.go
;;; note: source file /home/rob/guix/gnu/packages/haskell.scm
;;;       newer than compiled /run/current-system/profile/lib/guile/2.2/site-ccache/gnu/packages/haskell.go
ice-9/boot-9.scm:752:25: In procedure dispatch-exception:
Syntax error:
unknown location: package: invalid field specifier in form —-

There are number of ways the error output could be improved. Ideally, I’d
like to see the offending line of gnu/packages/haskell.scm pin-pointed,
and/or the start of the enclosing package definition. But if that’s maybe
difficult due to macro expansion issues, at least knowing which file failed
to compile would be great. gnu/packages/haskell.scm does fail to compile
by itself:

$ guild compile gnu/packages/haskell.scm 
ice-9/boot-9.scm:752:25: In procedure dispatch-exception:
Syntax error:
unknown location: package: invalid field specifier in form —-


This is on a pretty up to date Guix install.

$ guild --version
guild (GNU Guile) 2.2.4

Message #8 received at 36079 <at> debbugs.gnu.org (full text, mbox):

From: Ricardo Wurmus <rekado <at> elephly.net>
To: 36079 <at> debbugs.gnu.org
Cc: Robert Vollmert <rob <at> vllmrt.net>
Subject: Re: bug#36079: unhelpful error message
Date: Sun, 09 Jun 2019 22:09:42 +0200

Hi Robert,

> Working on Guix, I encountered the following:
>
> Within a guix checkout, I edited gnu/packages/haskell.scm, accidentally
> making a Haskell comment:
>
>     (arguments
>      `(#:tests? #f)) -- sporadic failure: https://github.com/fpco/streaming-commons/issues/49
>
> Then I tried to keep working on my in-development package, and was able to trace
> the `guix build` error back to the following:
>
> $ ./pre-inst-env guild compile ../modules/postgrest.scm
> ;;; note: source file /home/rob/guix/gnu/packages/haskell.scm
> ;;;       newer than compiled /home/rob/guix/gnu/packages/haskell.go
> ;;; note: source file /home/rob/guix/gnu/packages/haskell.scm
> ;;;       newer than compiled /run/current-system/profile/lib/guile/2.2/site-ccache/gnu/packages/haskell.go
> ice-9/boot-9.scm:752:25: In procedure dispatch-exception:
> Syntax error:
> unknown location: package: invalid field specifier in form —-

This error is produced by the “package” macro, which is of this form:

  (package
   (field value)
   (another-field its-value)
   …)

The macro has a number of valid field names and it tries to do some
simple validation.  That’s where the error comes from.  When “--” is
encountered it is in the position of a field, so the macro tries to be
helpful and reports that “--” is not a valid way to specify a field.

This error message is not produced by Guile.

> There are number of ways the error output could be improved. Ideally, I’d
> like to see the offending line of gnu/packages/haskell.scm pin-pointed,
> and/or the start of the enclosing package definition.

I agree that this would be nice.  Let’s move this to the Guix bug
tracker.

--
Ricardo

Message #11 received at 36079 <at> debbugs.gnu.org (full text, mbox):

From: Mark H Weaver <mhw <at> netris.org>
To: Ricardo Wurmus <rekado <at> elephly.net>
Cc: 36079 <at> debbugs.gnu.org, Robert Vollmert <rob <at> vllmrt.net>
Subject: Re: bug#36079: unhelpful error message
Date: Mon, 10 Jun 2019 20:29:48 -0400

Hi Ricardo and Robert,

Ricardo Wurmus <rekado <at> elephly.net> writes:

>> Working on Guix, I encountered the following:
>>
>> Within a guix checkout, I edited gnu/packages/haskell.scm, accidentally
>> making a Haskell comment:
>>
>>     (arguments
>>      `(#:tests? #f)) -- sporadic failure: https://github.com/fpco/streaming-commons/issues/49
>>
>> Then I tried to keep working on my in-development package, and was able to trace
>> the `guix build` error back to the following:
>>
>> $ ./pre-inst-env guild compile ../modules/postgrest.scm
>> ;;; note: source file /home/rob/guix/gnu/packages/haskell.scm
>> ;;;       newer than compiled /home/rob/guix/gnu/packages/haskell.go
>> ;;; note: source file /home/rob/guix/gnu/packages/haskell.scm
>> ;;;       newer than compiled /run/current-system/profile/lib/guile/2.2/site-ccache/gnu/packages/haskell.go
>> ice-9/boot-9.scm:752:25: In procedure dispatch-exception:
>> Syntax error:
>> unknown location: package: invalid field specifier in form —-
>
> This error is produced by the “package” macro, which is of this form:
>
>   (package
>    (field value)
>    (another-field its-value)
>    …)
>
> The macro has a number of valid field names and it tries to do some
> simple validation.  That’s where the error comes from.  When “--” is
> encountered it is in the position of a field, so the macro tries to be
> helpful and reports that “--” is not a valid way to specify a field.
>
> This error message is not produced by Guile.

Well, yes and no.  It is true that code in Guix is calling
'syntax-violation' to report the error.  However, it is also true that
Guix passes to 'syntax-violation' the syntax object corresponding to
“--”, which ideally should have source location information attached to
it.  If the syntax object in question represented a list or some other
heap-allocated value, it *would* have had source location information
attached, and that would have been included in the error message.

This issue is a longstanding limitation in Guile's source location
tracking.  The problem is that Guile uses Scheme's standard 'read'
procedure to read the source code, which uses plain Scheme symbols to
represent identifiers.  Scheme symbols with the same name are
indistinguishable, i.e. every occurrence of 'x' or '--' is represented
by precisely the same heap object, and therefore there's no way to
attach source information to each occurrence of a symbol.

Fixing this would involve abandoning Scheme's standard 'read' procedure
for reading source code, and instead using a different reader (not yet
written) that uses a different object type to represent identifiers and
immediate values.  Our macro expander would need to be modified to
support this new representation.

I believe this should be done, and I hope to find the energy to do it
some day.

       Mark

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