[PATCH 2/2] restore: default to HEAD when combining --worktree and --staged

[Eric Sunshine <sunshine@sunshineco.com>]

The default restore source for --worktree is the index, and the default
source for --staged is HEAD. However, when combining --worktree and
--staged in the same invocation, git-restore requires the source to be
specified explicitly via --source since it would otherwise be ambiguous
("should it restore from the index or from HEAD?"). This requirement
makes it cumbersome to restore a file in both the worktree and the
index.

However, HEAD is also a reasonably intuitive default restore source when
--worktree and --staged are combined. After all, if a user is asking to
throw away all local changes to a file (on disk and in the index)
without specifying a restore source explicitly -- and the user expects
the file to be restored from _somewhere_ -- then it is likely that the
user expects them to be restored from HEAD, which is an intuitive and
logical place to find a recent unadulterated copy of the file.

Therefore, make HEAD the default restore source when --worktree and
--staged are combined.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
---
 Documentation/git-restore.txt | 14 +++++++-------
 builtin/checkout.c            |  9 +++------
 t/t2070-restore.sh            | 12 +++++++++---
 3 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/Documentation/git-restore.txt b/Documentation/git-restore.txt
index 8906499637..5b61812e17 100644
--- a/Documentation/git-restore.txt
+++ b/Documentation/git-restore.txt
@@ -22,10 +22,10 @@ The command can also be used to restore the content in the index with
 `--staged`, or restore both the working tree and the index with
 `--staged --worktree`.
 
-By default, the restore sources for working tree and the index are the
-index and `HEAD` respectively. `--source` could be used to specify a
-commit as the restore source; it is required when combining `--staged`
-and `--worktree`.
+By default, the restore source for `--worktree` is the index, and the
+restore source for `--staged` is `HEAD`. When combining `--worktree` and
+`--staged`, the restore source is `HEAD`. `--source` can be used to specify
+a different commit as the restore source.
 
 See "Reset, restore and revert" in linkgit:git[1] for the differences
 between the three commands.
@@ -40,10 +40,10 @@ OPTIONS
 	tree. It is common to specify the source tree by naming a
 	commit, branch or tag associated with it.
 +
-If not specified, the default restore source for the working tree is
-the index, and the default restore source for the index is
+If not specified, the default restore source for `--worktree` is
+the index, and the default restore source for `--staged` is
 `HEAD`. When both `--staged` and `--worktree` are specified,
-`--source` must also be specified.
+the default restore source is `HEAD`.
 
 -p::
 --patch::
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 7a01d00f53..500c3e23ff 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1604,14 +1604,11 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 	}
 	if (opts->checkout_index < 0 || opts->checkout_worktree < 0)
 		BUG("these flags should be non-negative by now");
-	if (opts->checkout_index > 0 && opts->checkout_worktree > 0 &&
-	    !opts->from_treeish)
-		die(_("--source required when using --worktree and --staged"));
 	/*
-	 * convenient shortcut: "git restore --staged" equals
-	 * "git restore --staged --source HEAD"
+	 * convenient shortcut: "git restore --staged [--worktree]" equals
+	 * "git restore --staged [--worktree] --source HEAD"
 	 */
-	if (!opts->from_treeish && opts->checkout_index && !opts->checkout_worktree)
+	if (!opts->from_treeish && opts->checkout_index)
 		opts->from_treeish = "HEAD";
 
 	/*
diff --git a/t/t2070-restore.sh b/t/t2070-restore.sh
index 19efa21fdb..89e5a142c9 100755
--- a/t/t2070-restore.sh
+++ b/t/t2070-restore.sh
@@ -69,9 +69,15 @@ test_expect_success 'restore --staged uses HEAD as source' '
 	test_cmp expected actual
 '
 
-test_expect_success 'restore --worktree --staged requires --source' '
-	test_must_fail git restore --worktree --staged first.t 2>err &&
-	test_i18ngrep "source required when using --worktree and --staged" err
+test_expect_success 'restore --worktree --staged uses HEAD as source' '
+	test_when_finished git reset --hard &&
+	git show HEAD:./first.t >expected &&
+	echo dirty >>first.t &&
+	git add first.t &&
+	git restore --worktree --staged first.t &&
+	git show :./first.t >actual &&
+	test_cmp expected actual &&
+	test_cmp expected first.t
 '
 
 test_expect_success 'restore --ignore-unmerged ignores unmerged entries' '
-- 
2.26.2.526.g744177e7f7