autom4te partly swallows m4_pattern_forbid multi-line comments

[Hans Ulrich Niedermann]

If you have a command like

m4_pattern_forbid([SOME_PATTERN], [some
multi-line
comment])

in your configure.ac, the error message will only
contain the comment's first line.

My original test case was

dnl configure.ac - process with autoreconf
AC_INIT([autoconf m4_pattern_forbid error message bug], [0], [], [])
m4_pattern_forbid([FOOBAR], [Line 1 of error message
Line 2 of error message
Line 3 of error message])
FOOBAR
AC_OUTPUT

but this can be reduced to

dnl configure.ac - process with autoconf (without "re")
AS_INIT
m4_pattern_forbid([FOOBAR], [Line 1 of error message
Line 2 of error message
Line 3 of error message])
FOOBAR

In both test cases, the output will look like

configure.ac:2: error: line 1 of comment                                                                                               
     If this token and others are legitimate, please use m4_pattern_allow.
     See the Autoconf documentation.

It appears autom4te calls m4 and has m4 store all
m4_pattern_allow and m4_pattern_forbid invocations from
configure.ac into a file $tmp/patterns which consists of
lines like:

forbid:^AS_BLAH$:
forbid:FOOBAR:special comment
allow:AS_MEH

In the case of a multi-line comment, this will end up
looking like

forbid:^AS_BLAH$:
forbid:FOOBAR:Line 1 of error message
Line 2 of error message
Line 3 of error message
allow:AS_MEH

and autom4te's sub handle_output() will ignore all lines
not starting with either 'allow:' or 'forbid:'.

I can see these potential solutions:

 0. NOTABUG. Undocumented behaviour.
 1. Let m4 create the $tmp/patterns file converting
    multi-line comments into an escaped one-line form
    and let autom4te later unescape them.
 2. Let m4 create the $tmp/patterns file as-is, but have
    autom4te re-assemble multi-line comments.

I will reply to this mail with a quick-and-dirty patch
implementing 2.

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