[PATCH 1/1] Merge with untracked file that are the same without failure and test

[Jonathan <git.jonathan.bressat@gmail.com>]

When doing a merge while there is untracked files with the same name
as merged files, git refuses to proceed. This commit change this
behavior and make git overwrite files if their contents are the same.
This new behaviour is more pleasant for a user and will never be a
frustrating moment.

Add a if statement that check if the file has the same content as the
merged file thanks to the function ie_modified() (read-cache.c).
ie_modified () checks the status of both files, if they are different,
it verifies their contents.

Add new tests that need to pass to confirm that the new feature works.

Co-authored-by: COGONI Guillaume <cogoni.guillaume@gmail.com>
---
 t/t7615-merge-untracked.sh | 79 ++++++++++++++++++++++++++++++++++++++
 unpack-trees.c             |  4 ++
 2 files changed, 83 insertions(+)
 create mode 100755 t/t7615-merge-untracked.sh

diff --git a/t/t7615-merge-untracked.sh b/t/t7615-merge-untracked.sh
new file mode 100755
index 0000000000..71a34041d2
--- /dev/null
+++ b/t/t7615-merge-untracked.sh
@@ -0,0 +1,79 @@
+#!/bin/sh
+
+test_description='test when merge with untracked file'
+
+. ./test-lib.sh
+
+
+test_expect_success 'overwrite the file when fastforward and the same content' '
+    echo content >README.md &&
+    test_commit "init" README.md &&
+    git branch A &&
+    git checkout -b B &&
+    echo content >file &&
+    git add file &&
+    git commit -m "tracked" &&
+    git switch A &&
+    echo content >file &&
+    git merge B
+'
+
+test_expect_success 'merge fail with fastforward and different content' '
+    rm * &&
+    rm -r .git &&
+    git init &&
+    echo content >README.md &&
+    test_commit "init" README.md &&
+    git branch A &&
+    git checkout -b B &&
+    echo content >file &&
+    git add file &&
+    git commit -m "tracked" &&
+    git switch A &&
+    echo dif >file &&
+    test_must_fail git merge B
+'
+
+test_expect_success 'normal merge with untracked with the same content' '
+    rm * &&
+    rm -r .git &&
+    git init &&
+    echo content >README.md &&
+    test_commit "init" README.md &&
+    git branch A &&
+    git checkout -b B &&
+    echo content >fileB &&
+    echo content >file &&
+    git add fileB &&
+    git add file &&
+    git commit -m "tracked" &&
+    git switch A &&
+    echo content >fileA &&
+    git add fileA &&
+    git commit -m "exA" &&
+    echo content >file &&
+    git merge B -m "merge"
+'
+
+test_expect_success 'normal merge fail when untracked with different content' '
+    rm * &&
+    rm -r .git &&
+    git init &&
+    echo content >README.md &&
+    test_commit "init" README.md &&
+    git branch A &&
+    git checkout -b B &&
+    echo content >fileB &&
+    echo content >file &&
+    git add fileB &&
+    git add file &&
+    git commit -m "tracked" &&
+    git switch A &&
+    echo content >fileA &&
+    git add fileA &&
+    git commit -m "exA" &&
+    echo dif >file &&
+    test_must_fail git merge B -m "merge"
+'
+
+test_done
\ No newline at end of file
diff --git a/unpack-trees.c b/unpack-trees.c
index 360844bda3..834aca0da9 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -2259,6 +2259,10 @@ static int check_ok_to_remove(const char *name, int len, int dtype,
 			return 0;
 	}
 
+	if (!ie_modified(&o->result, ce, st, 0))
+		return 0;
+
+
 	return add_rejected_path(o, error_type, name);
 }
 
-- 
2.35.1.7.gc8609858e0.dirty