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git/git-merge-resolve.sh
Elijah Newren 24ba8b70c9 merge-resolve: abort if index does not match HEAD
As noted in commit 9822175d2b ("Ensure index matches head before
invoking merge machinery, round N", 2019-08-17), we have had a very
long history of problems with failing to enforce the requirement that
index matches HEAD when starting a merge.  One of the commits
referenced in the long tale of issues arising from lax enforcement of
this requirement was commit 55f39cf755 ("merge: fix misleading
pre-merge check documentation", 2018-06-30), which tried to document
the requirement and noted there were some exceptions.  As mentioned in
that commit message, the `resolve` strategy was the one strategy that
did not have an explicit index matching HEAD check, and the reason it
didn't was that I wasn't able to discover any cases where the
implementation would fail to catch the problem and abort, and didn't
want to introduce unnecessary performance overhead of adding another
check.

Well, today I discovered a testcase where the implementation does not
catch the problem and so an explicit check is needed.  Add a testcase
that previously would have failed, and update git-merge-resolve.sh to
have an explicit check.  Note that the code is copied from 3ec62ad9ff
("merge-octopus: abort if index does not match HEAD", 2016-04-09), so
that we reuse the same message and avoid making translators need to
translate some new message.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-07-22 21:45:22 -07:00

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#!/bin/sh
#
# Copyright (c) 2005 Linus Torvalds
# Copyright (c) 2005 Junio C Hamano
#
# Resolve two trees, using enhanced multi-base read-tree.
. git-sh-setup
# Abort if index does not match HEAD
if ! git diff-index --quiet --cached HEAD --
then
gettextln "Error: Your local changes to the following files would be overwritten by merge"
git diff-index --cached --name-only HEAD -- | sed -e 's/^/ /'
exit 2
fi
# The first parameters up to -- are merge bases; the rest are heads.
bases= head= remotes= sep_seen=
for arg
do
case ",$sep_seen,$head,$arg," in
*,--,)
sep_seen=yes
;;
,yes,,*)
head=$arg
;;
,yes,*)
remotes="$remotes$arg "
;;
*)
bases="$bases$arg "
;;
esac
done
# Give up if we are given two or more remotes -- not handling octopus.
case "$remotes" in
?*' '?*)
exit 2 ;;
esac
# Give up if this is a baseless merge.
if test '' = "$bases"
then
exit 2
fi
git update-index -q --refresh
git read-tree -u -m --aggressive $bases $head $remotes || exit 2
echo "Trying simple merge."
if result_tree=$(git write-tree 2>/dev/null)
then
exit 0
else
echo "Simple merge failed, trying Automatic merge."
if git merge-index -o git-merge-one-file -a
then
exit 0
else
exit 1
fi
fi