[RFC PATCH v4 07/10] unpack-trees: avoid nuking untracked dir in way of unmerged file

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

From: Elijah Newren <newren@gmail.com>

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 t/t2500-untracked-overwriting.sh |  2 +-
 unpack-trees.c                   | 35 ++++++++++++++++++++++++++++----
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/t/t2500-untracked-overwriting.sh b/t/t2500-untracked-overwriting.sh
index 18604360df8..5ec66058cfc 100755
--- a/t/t2500-untracked-overwriting.sh
+++ b/t/t2500-untracked-overwriting.sh
@@ -197,7 +197,7 @@ test_expect_failure 'git stash and untracked files' '
 	)
 '
 
-test_expect_failure 'git am --abort and untracked dir vs. unmerged file' '
+test_expect_success 'git am --abort and untracked dir vs. unmerged file' '
 	test_setup_sequencing am_abort_and_untracked &&
 	(
 		cd sequencing_am_abort_and_untracked &&
diff --git a/unpack-trees.c b/unpack-trees.c
index 37f769030ab..8408a8fcfff 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -2173,9 +2173,15 @@ static int icase_exists(struct unpack_trees_options *o, const char *name, int le
 	return src && !ie_match_stat(o->src_index, src, st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
 }
 
+enum absent_checking_type {
+	COMPLETELY_ABSENT,
+	ABSENT_ANY_DIRECTORY
+};
+
 static int check_ok_to_remove(const char *name, int len, int dtype,
 			      const struct cache_entry *ce, struct stat *st,
 			      enum unpack_trees_error_types error_type,
+			      enum absent_checking_type absent_type,
 			      struct unpack_trees_options *o)
 {
 	const struct cache_entry *result;
@@ -2209,6 +2215,10 @@ static int check_ok_to_remove(const char *name, int len, int dtype,
 		return 0;
 	}
 
+	/* If we only care about directories, then we can remove */
+	if (absent_type == ABSENT_ANY_DIRECTORY)
+		return 0;
+
 	/*
 	 * The previous round may already have decided to
 	 * delete this path, which is in a subdirectory that
@@ -2229,6 +2239,7 @@ static int check_ok_to_remove(const char *name, int len, int dtype,
  */
 static int verify_absent_1(const struct cache_entry *ce,
 			   enum unpack_trees_error_types error_type,
+			   enum absent_checking_type absent_type,
 			   struct unpack_trees_options *o)
 {
 	int len;
@@ -2255,7 +2266,8 @@ static int verify_absent_1(const struct cache_entry *ce,
 								NULL, o);
 			else
 				ret = check_ok_to_remove(path, len, DT_UNKNOWN, NULL,
-							 &st, error_type, o);
+							 &st, error_type,
+							 absent_type, o);
 		}
 		free(path);
 		return ret;
@@ -2270,7 +2282,7 @@ static int verify_absent_1(const struct cache_entry *ce,
 
 		return check_ok_to_remove(ce->name, ce_namelen(ce),
 					  ce_to_dtype(ce), ce, &st,
-					  error_type, o);
+					  error_type, absent_type, o);
 	}
 }
 
@@ -2280,14 +2292,23 @@ static int verify_absent(const struct cache_entry *ce,
 {
 	if (!o->skip_sparse_checkout && (ce->ce_flags & CE_NEW_SKIP_WORKTREE))
 		return 0;
-	return verify_absent_1(ce, error_type, o);
+	return verify_absent_1(ce, error_type, COMPLETELY_ABSENT, o);
+}
+
+static int verify_absent_if_directory(const struct cache_entry *ce,
+				      enum unpack_trees_error_types error_type,
+				      struct unpack_trees_options *o)
+{
+	if (!o->skip_sparse_checkout && (ce->ce_flags & CE_NEW_SKIP_WORKTREE))
+		return 0;
+	return verify_absent_1(ce, error_type, ABSENT_ANY_DIRECTORY, o);
 }
 
 static int verify_absent_sparse(const struct cache_entry *ce,
 				enum unpack_trees_error_types error_type,
 				struct unpack_trees_options *o)
 {
-	return verify_absent_1(ce, error_type, o);
+	return verify_absent_1(ce, error_type, COMPLETELY_ABSENT, o);
 }
 
 static int merged_entry(const struct cache_entry *ce,
@@ -2361,6 +2382,12 @@ static int merged_entry(const struct cache_entry *ce,
 		 * Previously unmerged entry left as an existence
 		 * marker by read_index_unmerged();
 		 */
+		if (verify_absent_if_directory(merge,
+				  ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o)) {
+			discard_cache_entry(merge);
+			return -1;
+		}
+
 		invalidate_ce_path(old, o);
 	}
 
-- 
2.33.0.1404.g83021034c5d