doc: use bold style for man page references

It's more common to use bold style than not,
for references to other man pages.
Ideally each man page renderer would highlight references,
but currently some rely on styles in the page itself.

* man/help2man: Implement a --bold-refs option that
will mark up references like "name(1)" with bold
style around the "name" component.
* man/local.mk: Pass --bold-refs to our help2man unless disabled.
* configure.ac: Add a --disable-bold-man-page-references option.
Addresses https://bugs.gnu.org/53977

3 files changed, 28 insertions, 2 deletions

diff --git a/configure.ac b/configure.ac
index 453baccff..7e4afc96f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -114,6 +114,20 @@ if test "$gl_single_binary" = 'symlinks'; then
 fi
 AM_CONDITIONAL([SINGLE_BINARY], [test "$gl_single_binary" != no])
 
+AC_ARG_ENABLE([bold-man-page-references],
+  [AS_HELP_STRING([--disable-bold-man-page-references],
+     [When generating man pages, do not apply bold style around any
+      references like name(1) etc.])],
+  [gl_bold_manpages=yes ;
+   case $enableval in
+     no|yes) gl_bold_manpages=$enableval ;;
+     *)      AC_MSG_ERROR([bad value $enableval for bold-man-page-references.
+                           Options are: yes, no.]) ;;
+   esac],
+  [gl_bold_manpages=yes]
+)
+AM_CONDITIONAL([BOLD_MAN_REFS], [test "$gl_bold_manpages" != no])
+
 AC_ARG_ENABLE([gcc-warnings],
   [AS_HELP_STRING([--enable-gcc-warnings@<:@=TYPE@:>@],
     [control generation of GCC warnings.  The TYPE 'no' disables
diff --git a/man/help2man b/man/help2man
index 99a1c9263..581f69ddd 100755
--- a/man/help2man
+++ b/man/help2man
@@ -78,6 +78,7 @@ Usage: %s [OPTION]... EXECUTABLE
  -p, --info-page=TEXT    name of Texinfo manual
  -N, --no-info           suppress pointer to Texinfo manual
  -l, --libtool           exclude the `lt-' from the program name
+ -b, --bold-refs         apply bold style to references
      --help              print this help, then exit
      --version           print version number, then exit
 
@@ -99,7 +100,7 @@ my $help_option = '--help';
 my $version_option = '--version';
 my $discard_stderr = 1;
 my ($opt_name, @opt_include, $opt_output, $opt_info, $opt_no_info, $opt_libtool,
-    $version_text);
+    $opt_bold_refs, $version_text);
 
 my %opt_def = (
     'n|name=s'		 => \$opt_name,
@@ -113,6 +114,7 @@ my %opt_def = (
     'p|info-page=s'	 => \$opt_info,
     'N|no-info'		 => \$opt_no_info,
     'l|libtool'		 => \$opt_libtool,
+    'b|bold-refs'	 => \$opt_bold_refs,
     'help'		 => sub { print $help_info; exit },
     'version'		 => sub { print $version_info; exit },
     'h|help-option=s'	 => \$help_option,
@@ -714,6 +716,13 @@ for my $sect (@pre, (grep !$filter{$_}, @sections), @post)
 
 	for ($include{$sect})
 	{
+            # Add bold style around referenced pages.
+            if ($opt_bold_refs)
+            {
+                # This will ignore entries already marked up (with \)
+                s/(^|\s|,)([\[\w\x83]+)\(([1-9][[:lower:]]?)\)/$1\\fB$2\\fP($3)/g;
+            }
+
 	    # Replace leading dot, apostrophe, backslash and hyphen
 	    # tokens.
 	    s/\x80/\\&./g;
diff --git a/man/local.mk b/man/local.mk
index 0822536c8..46ed35a40 100644
--- a/man/local.mk
+++ b/man/local.mk
@@ -24,7 +24,10 @@ run_help2man = $(SHELL) $(srcdir)/man/dummy-man
 else
 ## Graceful degradation for systems lacking perl.
 if HAVE_PERL
-run_help2man = $(PERL) -- $(srcdir)/man/help2man
+if BOLD_MAN_REFS
+help2man_OPTS=--bold-refs
+endif
+run_help2man = $(PERL) -- $(srcdir)/man/help2man $(help2man_OPTS)
 else
 run_help2man = $(SHELL) $(srcdir)/man/dummy-man
 endif