Change unpack_trees' 'reset' flag into an enum

Traditionally, unpack_trees_options->reset was used to signal that it
was okay to delete any untracked files in the way.  This was used by
`git read-tree --reset`, but then started appearing in other places as
well.  However, many of the other uses should not be deleting untracked
files in the way.  Change this value to an enum so that a value of 1
(i.e. "true") can be split into two:
   UNPACK_RESET_PROTECT_UNTRACKED,
   UNPACK_RESET_OVERWRITE_UNTRACKED
In order to catch accidental misuses (i.e. where folks call it the way
they traditionally used to), define the special enum value of
   UNPACK_RESET_INVALID = 1
which will trigger a BUG().

Modify existing callers so that
   read-tree --reset
   reset --hard
   checkout --force
continue using the UNPACK_RESET_OVERWRITE_UNTRACKED logic, while other
callers, including
   am
   checkout without --force
   stash  (though currently dead code; reset always had a value of 0)
   numerous callers from rebase/sequencer to reset_head()
will use the new UNPACK_RESET_PROTECT_UNTRACKED value.

Also, note that it has been reported that 'git checkout <treeish>
<pathspec>' currently also allows overwriting untracked files[1].  That
case should also be fixed, but it does not use unpack_trees() and thus
is outside the scope of the current changes.

[1] https://lore.kernel.org/git/15dad590-087e-5a48-9238-5d2826950506@gmail.com/

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/unpack-trees.c b/unpack-trees.c
index 9ccb991084..3fff506156 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1694,6 +1694,9 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	int free_pattern_list = 0;
 	struct dir_struct dir = DIR_INIT;
 
+	if (o->reset == UNPACK_RESET_INVALID)
+		BUG("o->reset had a value of 1; should be UNPACK_TREES_*_UNTRACKED");
+
 	if (len > MAX_UNPACK_TREES)
 		die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
 	if (o->dir)
@@ -1708,6 +1711,10 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		ensure_full_index(o->dst_index);
 	}
 
+	if (o->reset == UNPACK_RESET_OVERWRITE_UNTRACKED &&
+	    o->preserve_ignored)
+		BUG("UNPACK_RESET_OVERWRITE_UNTRACKED incompatible with preserved ignored files");
+
 	if (!o->preserve_ignored) {
 		o->dir = &dir;
 		o->dir->flags |= DIR_SHOW_IGNORED;
@@ -2231,7 +2238,8 @@ static int verify_absent_1(const struct cache_entry *ce,
 	int len;
 	struct stat st;
 
-	if (o->index_only || o->reset || !o->update)
+	if (o->index_only || !o->update ||
+	    o->reset == UNPACK_RESET_OVERWRITE_UNTRACKED)
 		return 0;
 
 	len = check_leading_path(ce->name, ce_namelen(ce), 0);