Add new git-backport.py script.

contrib/ChangeLog:

	* gcc-git-customization.sh: Use git-backport.py to drop
	all changes for ChangeLog files.
	* git-backport.py: New file.

contrib/gcc-git-customization.sh

@@ -26,7 +26,7 @@ git config alias.gcc-descr \!"f() { if test \${1:-no} = --full; then c=\${2:-mas
 git config alias.gcc-undescr \!"f() { o=\$(git config --get gcc-config.upstream); r=\$(echo \$1 | sed -n 's,^r\\([0-9]\\+\\)-[0-9]\\+\$,\\1,p'); n=\$(echo \$1 | sed -n 's,^r[0-9]\\+-\\([0-9]\\+\\)\$,\\1,p'); test -z \$r && echo Invalid id \$1 && exit 1; h=\$(git rev-parse --verify --quiet \${o:-origin}/releases/gcc-\$r); test -z \$h && h=\$(git rev-parse --verify --quiet \${o:-origin}/master); p=\$(git describe --all --match 'basepoints/gcc-'\$r \$h | sed -n 's,^\\(tags/\\)\\?basepoints/gcc-[0-9]\\+-\\([0-9]\\+\\)-g[0-9a-f]*\$,\\2,p;s,^\\(tags/\\)\\?basepoints/gcc-[0-9]\\+\$,0,p'); git rev-parse --verify \$h~\$(expr \$p - \$n); }; f"
 
 git config alias.gcc-verify '!f() { "`git rev-parse --show-toplevel`/contrib/gcc-changelog/git_check_commit.py" $@; } ; f'
-git config alias.gcc-backport '!f() { rev=$1; git cherry-pick -x $@; } ; f'
+git config alias.gcc-backport '!f() { "`git rev-parse --show-toplevel`/contrib/git-backport.py" $@; } ; f'
 git config alias.gcc-mklog '!f() { "`git rev-parse --show-toplevel`/contrib/mklog.py" $@; } ; f'
 git config alias.gcc-commit-mklog '!f() { GCC_FORCE_MKLOG=1 git commit "$@"; }; f'
 

contrib/git-backport.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2020 Free Software Foundation, Inc.
+#
+# This file is part of GCC.
+#
+# GCC 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 3, or (at your option)
+# any later version.
+#
+# GCC 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 GCC; see the file COPYING.  If not, write to
+# the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+# Boston, MA 02110-1301, USA.
+
+import argparse
+import subprocess
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(description='Backport a git revision and '
+                                     'stash all ChangeLog files.')
+    parser.add_argument('revision', help='Revision')
+    args = parser.parse_args()
+
+    r = subprocess.run('git cherry-pick -x %s' % args.revision, shell=True)
+    if r.returncode == 0:
+        cmd = 'git show --name-only --pretty="" -- "*ChangeLog" |' \
+              'xargs git checkout HEAD~'
+        subprocess.check_output(cmd, shell=True)
+        subprocess.check_output('git commit --amend --no-edit', shell=True)
+    else:
+        # 1) remove all ChangeLog files from conflicts
+        out = subprocess.check_output('git diff --name-only --diff-filter=U',
+                                      shell=True,
+                                      encoding='utf8')
+        conflicts = out.strip().split('\n')
+        changelogs = [c for c in conflicts if c.endswith('ChangeLog')]
+        if changelogs:
+            cmd = 'git checkout --theirs %s' % '\n'.join(changelogs)
+            subprocess.check_output(cmd, shell=True)
+        # 2) remove all ChangeLog files from index
+        cmd = 'git diff --name-only --diff-filter=M HEAD'
+        out = subprocess.check_output(cmd, shell=True, encoding='utf8')
+        out = out.strip().split('\n')
+        modified = [c for c in out if c.endswith('ChangeLog')]
+        for m in modified:
+            subprocess.check_output('git reset %s' % m, shell=True)
+            subprocess.check_output('git checkout %s' % m, shell=True)
+
+        # try to continue
+        if len(conflicts) == len(changelogs):
+            subprocess.check_output('git cherry-pick --continue', shell=True)
+        else:
+            print('Please resolve all remaining file conflicts.')