bug#55025: [PATCH] New "posix" automake option.

[Vincent Lefevre]

This patch is from https://bugs.gnu.org/55025.

* lib/Automake/Options.pm: declare "posix" option.
* bin/automake.in: if the "posix" option is present, add
a .POSIX special target as the first non-comment line in
the Makefile.in files.
* NEWS: mention this.
* doc/automake.texi: likewise.
---
 NEWS                    | 2 ++
 bin/automake.in         | 7 +++++++
 doc/automake.texi       | 6 ++++++
 lib/Automake/Options.pm | 1 +
 4 files changed, 16 insertions(+)

diff --git a/NEWS b/NEWS
index ced0fd640..821ae0cf1 100644
--- a/NEWS
+++ b/NEWS
@@ -30,6 +30,8 @@ New in 1.17:
     as given in the Makefile.am will be used.  If @setfilename is present,
     it should be the basename of the Texinfo file, extended with .info.
 
+  - New option "posix" to generate a .POSIX special target.
+
 * Bugs fixed
 
   - Generated file timestamp checks now handle filesystems with sub-second
diff --git a/bin/automake.in b/bin/automake.in
index 369a47fa2..edc0488b8 100644
--- a/bin/automake.in
+++ b/bin/automake.in
@@ -8126,6 +8126,13 @@ sub generate_makefile
   my $output =
     "$output_vars$output_all$output_header$output_rules$output_trailer";
 
+  # The .POSIX special target must be the first non-comment line;
+  # otherwise, the behavior of "make" is unspecified by POSIX.
+  if (option 'posix')
+    {
+      $output =~ s/^((#.*)?\n)*\K/.POSIX:\n\n/;
+    }
+
   # Decide whether we must update the output file or not.
   # We have to update in the following situations.
   #  * $force_generation is set.
diff --git a/doc/automake.texi b/doc/automake.texi
index d14b769fd..97e3e3475 100644
--- a/doc/automake.texi
+++ b/doc/automake.texi
@@ -10679,6 +10679,12 @@ are ordinarily automatically provided by Automake.
 Don't require @file{texinfo.tex}, even if there are texinfo files in
 this directory.
 
+@item @option{posix}
+@cindex Option, @option{posix}
+@opindex posix
+Generate a @code{.POSIX} special target as the first non-comment line in
+the @file{Makefile.in} files.
+
 @item @option{serial-tests}
 @cindex Option, @option{serial-tests}
 @opindex serial-tests
diff --git a/lib/Automake/Options.pm b/lib/Automake/Options.pm
index 69fc2ecb5..22d527fac 100644
--- a/lib/Automake/Options.pm
+++ b/lib/Automake/Options.pm
@@ -290,6 +290,7 @@ sub _is_valid_easy_option ($)
     no-installman
     no-texinfo.tex
     nostdinc
+    posix
     readme-alpha
     serial-tests
     parallel-tests
-- 
2.42.0