[PATCH 1/2] restore: require --source 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. When combining --worktree and --staged in
the same invocation, the restore source is ambiguous ("should it restore
from the index or from HEAD?"). To avoid such ambiguity, the git-restore
documentation has always stated that --source must be used when
combining --worktree and --staged. However, this restriction is not
actually enforced. Address this deficiency by making the implementation
match the documented behavior (to wit, error out if --source is not
specified when combining --worktree and --staged).

While at it, enhance the documentation to mention the --source
requirement prominently in the "Description" section (rather than only
in the description of the --source option itself).

Reported-by: Harri Mehtälä <harri.mehtala@finago.com>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
---
 Documentation/git-restore.txt | 3 ++-
 builtin/checkout.c            | 3 +++
 t/t2070-restore.sh            | 5 +++++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-restore.txt b/Documentation/git-restore.txt
index 8e3b339802..8906499637 100644
--- a/Documentation/git-restore.txt
+++ b/Documentation/git-restore.txt
@@ -24,7 +24,8 @@ The command can also be used to restore the content in the index with
 
 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.
+commit as the restore source; it is required when combining `--staged`
+and `--worktree`.
 
 See "Reset, restore and revert" in linkgit:git[1] for the differences
 between the three commands.
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 8bc94d392b..7a01d00f53 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1604,6 +1604,9 @@ 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"
diff --git a/t/t2070-restore.sh b/t/t2070-restore.sh
index 076d0df7fc..19efa21fdb 100755
--- a/t/t2070-restore.sh
+++ b/t/t2070-restore.sh
@@ -69,6 +69,11 @@ 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 --ignore-unmerged ignores unmerged entries' '
 	git init unmerged &&
 	(
-- 
2.26.2.526.g744177e7f7