回复: [BUG] git merge sometimes loses changes from one branch

From

GTGuo Tingsheng <coricraft16@outlook.com>

Date

Oct 28, 2025, 16:12 UTC

Message-ID

<SN6PR03MB4285533B67E31D36172A4C34AEFDA@SN6PR03MB4285.namprd03.prod.outlook.com>

In-Reply-To

<CABPp-BGeZ6no5LdBGKjykQLqUHRjFis7ZtGdEwnzg0gy_CkLqA@mail.gmail.com>

Hello Git developers,

To make it easier to reproduce, I have open-sourced this example in a public repository:
Repository: https://github.com/CoriWork/bug-replay.git

You can clone the repository and follow the README.md to replay the bug!

---

Environment:
- Git version: 2.43.0
- OS: Ubuntu 24.04 LTS

---

Steps to reproduce:
1. On branch B, modify a file at a certain location:

@@ -1068,9 +1026,7 @@ public final class AutoBuilderCompilationTest {
             "  }",
             "}");
     Compilation compilation =
-        javac()
-            .withProcessors(new AutoBuilderProcessor())
-            .compile(javaFileObject);
+        javac().withProcessors(new AutoBuilderProcessor()).compile(javaFileObject);
     assertThat(compilation).failed();
     assertThat(compilation)
         .hadErrorContaining(

2. On branch A, make no changes to this location.

3. Merge branch A and branch B.

---

Expected result:
The merge should retain the change made in branch B:

@@ -1068,9 +1026,7 @@ public final class AutoBuilderCompilationTest {
             "  }",
             "}");
     Compilation compilation =
-        javac()
-            .withProcessors(new AutoBuilderProcessor())
-            .compile(javaFileObject);
+        javac().withProcessors(new AutoBuilderProcessor()).compile(javaFileObject);
     assertThat(compilation).failed();
     assertThat(compilation)
         .hadErrorContaining(

Actual result:
Git sometimes produces a merged result where the modification from branch A
is lost, yielding:

   @@ -1026,7 +1028,9 @@
   public final class AutoBuilderCompilationTest {
                "  }",
                "}");
       Compilation compilation =
           javac()
            .withProcessors(new AutoBuilderProcessor())
            .compile(javaFileObject);

---

Additional information:
- This issue occurs even when branch B does not modify the same location.
- It appears to happen deterministically under a specific construction that
  splits one patch into two disjoint sets of hunks, applies them separately
  to create two branches, and then merges them back.
- The merged result can differ from the expected content of the original commit.

Thank you for your time and your work maintaining Git.

Best regards,  
Guo Tingsheng  
< CoriCraft16@outlook.com >