GNU bug report logs - #16314
Macro dependency tracking issue in guile auto compiler

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From: Panicz Maciej Godek <godek.maciek <at> gmail.com>
To: 16314 <at> debbugs.gnu.org
Subject: bug#16314: Macro dependency tracking issue in guile auto compiler
Date: Wed, 1 Jan 2014 14:19:53 +0100

Hi,
I've noticed that if macros are ever used in the process
of auto-compilation, the dependency is forgotten, so
even if a module that contains the definition of a macro
gets recompiled, the module that uses the macro remains
unchanged.

For example, consider the following situation. I have
two modules and a program that uses one of them.
The directory tree looks like this:
.
|-- module
|    |-- master.scm
|    `-- slave.scm
`-- program.scm

The module/master.scm contains the following code:

--8<---------------cut here---------------start------------->8---
(define-module (module master)
  #:export (macro function))

(define-syntax-rule (macro)
  (display "macro expanded"))

(define (function)
  (display "function called"))
--8<---------------cut here---------------end--------------->8---
The module/slave.scm uses the master module:

--8<---------------cut here---------------start------------->8---
(define-module (module slave)
  #:use-module (module master)
  #:export (f))

(define (f)
  (macro))
--8<---------------cut here---------------end--------------->8---

But the program.scm uses only the slave module:

--8<---------------cut here---------------start------------->8---
(use-modules (module slave))

(f)
--8<---------------cut here---------------end--------------->8---

If I run the program, I get the following result:
user cwd $ GUILE_LOAD_PATH=. guile -s program.scm
;;; <auto-compilation of program.scm>
;;; <auto-compilation of module/slave.scm>
;;; <auto-compilation of module/master.scm>
macro expandeduser cwd $

Oops, I forgot to add a trailing newline. But that's no problem!
I edit the body of module/master.scm:
-  (display "macro expanded"))
+  (display "macro expanded!\n"))

and then run the program once again:
user cwd $ GUILE_LOAD_PATH=. guile -s program.scm
;;; <auto-compilation of module/master.scm>
macro expandeduser cwd $

Damn! That didn't work. See the problem? If I modify
a module that exports any syntax definition, it should
force all the modules that use it be recompiled -- otherwise
the auto-compilation feature is only a potential source
of confusion, and forcing recompilation of all user modules
if at least one of them has been modified seems to be
a less confusing default strategy, if a more fine-grained
dependency tracking is too difficult to implement.

I've tested that behaviour under guile 2.0.5, guile-2.0.9,
guile-2.0.9.98-36c40 from hydra and guile-2.1.0.545-61989
from git, and everywhere it worked the same.

Regards,
M.

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