[PATCH 1/2] builtin/checkout: fix `git checkout -p HEAD...` bug

[Denton Liu <liu.denton@gmail.com>]

Running `git checkout -p` with a merge-base rev results in an error:

	$ git checkout -p HEAD...
	usage: git diff-index [-m] [--cached] [<common-diff-options>] <tree-ish> [<path>...]
	common diff options:
	  -z            output diff-raw with lines terminated with NUL.
	  -p            output patch format.
	  -u            synonym for -p.
	  --patch-with-raw
			output both a patch and the diff-raw format.
	  --stat        show diffstat instead of patch.
	  --numstat     show numeric diffstat instead of patch.
	  --patch-with-stat
			output a patch and prepend its diffstat.
	  --name-only   show only names of changed files.
	  --name-status show names and status of changed files.
	  --full-index  show full object name on index lines.
	  --abbrev=<n>  abbreviate object names in diff-tree header and diff-raw.
	  -R            swap input file pairs.
	  -B            detect complete rewrites.
	  -M            detect renames.
	  -C            detect copies.
	  --find-copies-harder
			try unchanged files as candidate for copy detection.
	  -l<n>         limit rename attempts up to <n> paths.
	  -O<file>      reorder diffs according to the <file>.
	  -S<string>    find filepair whose only one side contains the string.
	  --pickaxe-all
			show all files diff when -S is used and hit is found.
	  -a  --text    treat all files as text.

	Cannot close git diff-index --cached --numstat --summary HEAD... -- () at <redacted>/libexec/git-core/git-add--interactive line 183.

This happens because checkout passes the literal argument (in the
example, `HEAD...`) to diff-index which does not recognise merge-base
revs.

Fix this by using the hex of the found commit instead of the given name.
Note that "HEAD" is handled specially in run_add_interactive() so it's
explicitly not changed.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
---
 builtin/checkout.c        | 14 +++++++++++++-
 t/t2016-checkout-patch.sh |  7 +++++++
 t/t2071-restore-patch.sh  |  8 ++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 0951f8fee5..95122e16ed 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -471,6 +471,18 @@ static int checkout_paths(const struct checkout_opts *opts,
 
 	if (opts->patch_mode) {
 		const char *patch_mode;
+		const char *rev = new_branch_info->name;
+		char rev_oid[GIT_MAX_HEXSZ + 1];
+
+		/*
+		 * Since rev can be in the form of `<a>...<b>`, we must replace
+		 * the name with the hex of the commit for the
+		 * run_add_interactive() machinery to work properly. However,
+		 * there is special logic for the HEAD case so we mustn't
+		 * replace that.
+		 */
+		if (rev && strcmp(rev, "HEAD"))
+			rev = oid_to_hex_r(rev_oid, &new_branch_info->commit->object.oid);
 
 		if (opts->checkout_index && opts->checkout_worktree)
 			patch_mode = "--patch=checkout";
@@ -481,7 +493,7 @@ static int checkout_paths(const struct checkout_opts *opts,
 		else
 			BUG("either flag must have been set, worktree=%d, index=%d",
 			    opts->checkout_worktree, opts->checkout_index);
-		return run_add_interactive(new_branch_info->name, patch_mode, &opts->pathspec);
+		return run_add_interactive(rev, patch_mode, &opts->pathspec);
 	}
 
 	repo_hold_locked_index(the_repository, &lock_file, LOCK_DIE_ON_ERROR);
diff --git a/t/t2016-checkout-patch.sh b/t/t2016-checkout-patch.sh
index 47aeb0b167..999620e507 100755
--- a/t/t2016-checkout-patch.sh
+++ b/t/t2016-checkout-patch.sh
@@ -59,6 +59,13 @@ test_expect_success PERL 'git checkout -p HEAD with change already staged' '
 	verify_state dir/foo head head
 '
 
+test_expect_success PERL 'git checkout -p HEAD^...' '
+	# the third n is to get out in case it mistakenly does not apply
+	test_write_lines n y n | git checkout -p HEAD^... &&
+	verify_saved_state bar &&
+	verify_state dir/foo parent parent
+'
+
 test_expect_success PERL 'git checkout -p HEAD^' '
 	# the third n is to get out in case it mistakenly does not apply
 	test_write_lines n y n | git checkout -p HEAD^ &&
diff --git a/t/t2071-restore-patch.sh b/t/t2071-restore-patch.sh
index 98b2476e7c..b5c5c0ff7e 100755
--- a/t/t2071-restore-patch.sh
+++ b/t/t2071-restore-patch.sh
@@ -60,6 +60,14 @@ test_expect_success PERL 'git restore -p --source=HEAD^' '
 	verify_state dir/foo parent index
 '
 
+test_expect_success PERL 'git restore -p --source=HEAD^...' '
+	set_state dir/foo work index &&
+	# the third n is to get out in case it mistakenly does not apply
+	test_write_lines n y n | git restore -p --source=HEAD^... &&
+	verify_saved_state bar &&
+	verify_state dir/foo parent index
+'
+
 test_expect_success PERL 'git restore -p handles deletion' '
 	set_state dir/foo work index &&
 	rm dir/foo &&
-- 
2.28.0.942.g77c4c6094c