automake: support embedded \# in variable appends

Fixes automake bug https://bugs.gnu.org/7610.

Use of \# is not portable.  POSIX does not provide any way of retaining
the # marker in variables.  There is wide spread support for \# though
in GNU & BSD Make implementations.

Today, with plain variable assignments, Automake leaves the line alone:
  foo = blah\#blah
This will leave it to the implementation to decide what to do.  But if
you try to append to it, Automake follows POSIX and strips it:
  foo = blah\#blah
  foo += what
  -> foo = blah\ what

Instead, let's issue a portability warning whenever \# is used, even if
it isn't being appended, and do not strip the \# when appending.  Now:
  foo = blah\#blah
  foo += what
  -> warning: escaping \# comment markers is not portable
  -> foo = blah\#blah what

* NEWS: Mention change in \# handling.
* lib/Automake/VarDef.pm: Do not strip # if escaped.
* lib/Automake/Variable.pm: Warn if \# is used.
* t/comment12.sh: New test.
* t/comments-escaped-in-var.sh: New test.
* t/list-of-tests.mk: Add comment12.sh & comments-escaped-in-var.sh.

6 files changed, 100 insertions, 1 deletions

diff --git a/NEWS b/NEWS
index 512cdecd0..665d8329d 100644
--- a/NEWS
+++ b/NEWS
@@ -26,6 +26,9 @@ New in 1.17:
     drop support for them has been reversed.  The ACCEPT_INFERIOR_RM_PROGRAM
     setting no longer exists.
 
+  - Variables using escaped \# will trigger portability warnings, but be
+    retained when appended.  GNU Make & BSD Makes are known to support it.
+
 * Obsolescent features:
 
   - py-compile no longer supports Python 0.x or 1.x versions.  Python 2.0,
diff --git a/lib/Automake/VarDef.pm b/lib/Automake/VarDef.pm
index 59af4036b..00d694a6f 100644
--- a/lib/Automake/VarDef.pm
+++ b/lib/Automake/VarDef.pm
@@ -188,7 +188,7 @@ sub append ($$$)
   #   VAR = foo # com bar
   # Furthermore keeping '#' would not be portable if the variable is
   # output on multiple lines.
-  $val =~ s/ ?#.*//;
+  $val =~ s/ ?(^|[^\\])#.*/$1/;
   # Insert a separator, if required.
   $val .= ' ' if $val;
   $self->{'value'} = $val . $value;
diff --git a/lib/Automake/Variable.pm b/lib/Automake/Variable.pm
index 4f6a88d61..1269d5d9f 100644
--- a/lib/Automake/Variable.pm
+++ b/lib/Automake/Variable.pm
@@ -857,6 +857,9 @@ sub define ($$$$$$$$)
   msg ('portability', $where, "':='-style assignments are not portable")
     if $type eq ':';
 
+  msg ('portability', $where, "escaping \\# comment markers is not portable")
+    if index ($value, '\#') != -1;
+
   check_variable_expansions ($value, $where);
 
   # If there's a comment, make sure it is \n-terminated.
diff --git a/t/comment12.sh b/t/comment12.sh
new file mode 100644
index 000000000..e98159e40
--- /dev/null
+++ b/t/comment12.sh
@@ -0,0 +1,44 @@
+#! /bin/sh
+# Copyright (C) 2022 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+# Make sure that earlier comments are consumed when appending to it.
+
+. test-init.sh
+
+cat > Makefile.am << 'END'
+VAR1=# eat this comment
+VAR2 =# eat this comment
+VAR3 = # eat this comment
+VAR4 =	# eat this comment
+VAR5 = val# eat this comment
+VAR6 = val # eat this comment
+
+VAR1 += val
+VAR2 += val
+VAR3 += val
+VAR4 += val
+VAR5 +=
+VAR6 +=
+END
+
+$ACLOCAL
+$AUTOMAKE
+
+# For debugging.
+grep '^VAR' Makefile.in
+
+count=`grep '^VAR. = val$' Makefile.in | wc -l`
+[ $count -eq 6 ]
diff --git a/t/comments-escaped-in-var.sh b/t/comments-escaped-in-var.sh
new file mode 100644
index 000000000..e06c3f359
--- /dev/null
+++ b/t/comments-escaped-in-var.sh
@@ -0,0 +1,47 @@
+#! /bin/sh
+# Copyright (C) 2022 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+# Make sure Automake preserves escaped comments in the output.
+
+. test-init.sh
+
+cat >> configure.ac <<'END'
+AC_OUTPUT
+END
+
+cat > Makefile.am << 'END'
+# This value should be preserved.
+var = -DVAL='"\#xxx\#"'   # this should be stripped
+var += -DX=1  # this should be kept
+END
+
+$ACLOCAL
+
+# This should fail due to -Werror.
+$AUTOMAKE && exit 1
+
+# This should pass though.
+$AUTOMAKE -Wno-portability
+
+# For debugging.
+grep ^var Makefile.in
+
+# The full flag should be retained.
+grep '^var.*\\#xxx\\#.*DX=1' Makefile.in
+
+# Only the 2nd comment should be retained.
+grep '^var.*stripped' Makefile.in && exit 1 || :
+grep '^var.*should be kept' Makefile.in
diff --git a/t/list-of-tests.mk b/t/list-of-tests.mk
index 1601154e0..6bb6bef95 100644
--- a/t/list-of-tests.mk
+++ b/t/list-of-tests.mk
@@ -265,7 +265,9 @@ t/comment8.sh \
 t/comment9.sh \
 t/commen10.sh \
 t/commen11.sh \
+t/comment12.sh \
 t/comment-block.sh \
+t/comments-escaped-in-var.sh \
 t/comments-in-var-def.sh \
 t/compile.sh \
 t/compile2.sh \