m4 brackets question

[Bruno Haible]

Hi Eric,

Again, I've stumbled across a behaviour of brackets in autoconf macros that
I don't understand.

If in file m4/include_next.m4 at line 210 I add the following code

-------------------------------------------------------------------------------
               case "$host_os" in
                 mingw*)
                   dnl For the sake of native Windows compilers (excluding 
gcc), treat
                   dnl backslash as a directory separator, like /. Actually, 
these
                   dnl compilers use a double-backslash as directory separator, 
inside the
                   dnl   # line "filename"
                   dnl directives.
                   gl_absolute_header_sed='\#[/\\]]m4_defn([gl_HEADER_NAME])[#{
                     s#.*"\(.*[/\\]]m4_defn([gl_HEADER_NAME])[\)".*#\1#
                     s#^/[^/]#//&#
                     p
                     q
                   }'
                   ;;
                 *)
                   gl_absolute_header_sed='\#/]m4_defn([gl_HEADER_NAME])[#{
                     s#.*"\(.*/]m4_defn([gl_HEADER_NAME])[\)".*#\1#
                     s#^/[^/]#//&#
                     p
                     q
                   }'
                   ;;
               esac
-------------------------------------------------------------------------------

then the generated configure file (in a testdir
  $ ./gnulib-tool --create-testdir --dir=... --with-tests --single-configure 
math
) will contain the lines

-------------------------------------------------------------------------------
               case "$host_os" in
                 mingw*)
                                                                                
                                  gl_absolute_header_sed='\#[/\\]math.h#{
                     s#.*"\(.*[/\\]math.h\)".*#\1#
                     s#^/[^/]#//&#
                     p
                     q
                   }'
                   ;;
                 *)
                   gl_absolute_header_sed='\#/math.h#{
                     s#.*"\(.*/math.h\)".*#\1#
                     s#^/[^/]#//&#
                     p
                     q
                   }'
                   ;;
               esac
-------------------------------------------------------------------------------

which is OK. Note the brackets around /\\ have been preserved.

But when I rearrange the code like this:

-------------------------------------------------------------------------------
               case "$host_os" in
                 mingw*)
                   dnl For the sake of native Windows compilers (excluding gcc),
                   dnl treat backslash as a directory separator, like /.
                   dnl Actually, these compilers use a double-backslash as
                   dnl directory separator, inside the
                   dnl   # line "filename"
                   dnl directives.
                   gl_dirsep_regex='[/\\]'
                   ;;
                 *)
                   gl_dirsep_regex='/'
                   ;;
               esac
               
gl_absolute_header_sed='\#'"${gl_dirsep_regex}"']m4_defn([gl_HEADER_NAME])[#{
                   
s#.*"\(.*'"${gl_dirsep_regex}"']m4_defn([gl_HEADER_NAME])[\)".*#\1#
                   s#^/[^/]#//&#
                   p
                   q
                 }'
-------------------------------------------------------------------------------

then the configure file contains this:

-------------------------------------------------------------------------------
               case "$host_os" in
                 mingw*)
                                                                                
                                                     gl_dirsep_regex='/\\'
                   ;;
                 *)
                   gl_dirsep_regex='/'
                   ;;
               esac
               gl_absolute_header_sed='\#'"${gl_dirsep_regex}"'math.h#{
                   s#.*"\(.*'"${gl_dirsep_regex}"'math.h\)".*#\1#
                   s#^/[^/]#//&#
                   p
                   q
                 }'
-------------------------------------------------------------------------------

Note that the brackets around /\\ have been removed. Why??

And the brackets in the s#^/[^/]#//&# line have not been removed. I don't
see a difference in quotation level between the gl_dirsep_regex definition
and the gl_absolute_header_sed definition.

I'm using autoconf-2.68 and m4-1.4.15.

Bruno
-- 
In memoriam Sergei Tretyakov <http://en.wikipedia.org/wiki/Sergei_Tretyakov>