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Document some autom4te debugging tips.

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* doc/autoconf.texi (Debugging via autom4te): New node.
Suggested by Bruno Haible.

Signed-off-by: Eric Blake <ebb9@byu.net>
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Eric Blake 2009-07-25 06:51:59 -06:00
parent 3963d3ad3e
commit de8a83c3e9
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@ -1,5 +1,9 @@
2009-07-25 Eric Blake <ebb9@byu.net>
Document some autom4te debugging tips.
* doc/autoconf.texi (Debugging via autom4te): New node.
Suggested by Bruno Haible.
Fix font-lock.
* configure.ac (ac_cv_unsupported_fs_chars): Make editing easier.

62
doc/autoconf.texi
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@ -430,6 +430,7 @@ Programming in M4
* M4 Quotation:: Protecting macros from unwanted expansion
* Using autom4te:: The Autoconf executables backbone
* Programming in M4sugar:: Convenient pure M4 macros
* Debugging via autom4te:: Figuring out what M4 was doing
Programming in M4sh
@ -9414,6 +9415,7 @@ matter of fact, @emph{anything that is not documented must not be used}.
* M4 Quotation:: Protecting macros from unwanted expansion
* Using autom4te:: The Autoconf executables backbone
* Programming in M4sugar:: Convenient pure M4 macros
* Debugging via autom4te:: Figuring out what M4 was doing
@end menu
@node M4 Quotation
@ -12426,6 +12428,66 @@ Any token matching @var{pattern} is allowed, including if it matches an
@code{m4_pattern_forbid} pattern.
@end defmac
@node Debugging via autom4te
@section Debugging via autom4te
@cindex debugging tips
@cindex autom4te debugging tips
@cindex m4sugar debugging tips
At times, it is desirable to see what was happening inside m4, to see
why output was not matching expectations. However, post-processing done
by @command{autom4te} means that directly using the m4 builtin
@code{m4_traceon} is likely to interfere with operation. Also, frequent
diversion changes and the concept of forbidden tokens make it difficult
to use @code{m4_defn} to generate inline comments in the final output.
There are a couple of tools to help with this. One is the use of the
@option{--trace} option provided by @command{autom4te} (as well as each
of the programs that wrap @command{autom4te}, such as
@command{autoconf}), in order to inspect when a macro is called and with
which arguments. For example, when this paragraph was written, the
autoconf version could be found by:
@example
$ @kbd{autoconf --trace=AC_INIT}
configure.ac:23:AC_INIT:GNU Autoconf:2.63b.95-3963:bug-autoconf@@gnu.org
$ @kbd{autoconf --trace='AC_INIT:version is $2'}
version is 2.63b.95-3963
@end example
Another trick is using @code{m4_errprintn} to output debugging messages
to standard error with no further m4 expansion, and without interfering
with the post-processing done to standard output. For example, contrast
these two attempts to learn how @code{m4_dquote} is implemented:
@smallexample
$ @kbd{cat <<\EOF > foo.m4}
m4_init
try one: [m4_dquote is ]m4_defn([m4_dquote])
m4_divert([0])dnl
try two: [m4_dquote is ]m4_defn([m4_dquote])
m4_dquote([hi])
EOF
$ @kbd{autom4te --language=m4sugar -o foo foo.m4}
foo.m4:2: error: possibly undefined macro: m4_dquote
If this token and others are legitimate, please use m4_pattern_allow.
See the Autoconf documentation.
$ @kbd{cat foo}
try two: m4_dquote is [$@@]
[hi]
$ @kbd{cat <<\EOF > foo.m4}
m4_init
m4_errprintn([try one: m4_dquote is ]m4_defn([m4_dquote]))
m4_divert([0])dnl
m4_errprintn([try two: m4_dquote is ]m4_defn([m4_dquote]))dnl
m4_dquote([hi])
EOF
$ @kbd{autom4te --language=m4sugar foo.m4}
try one: m4_dquote is [$@@]
try two: m4_dquote is [$@@]
$ @kbd{cat foo}
[hi]
@end smallexample
@node Programming in M4sh
@chapter Programming in M4sh