Add get_merge_base to ddev git (#21340)

* method

* changelog

* changelog

* test

* test

* changelog

* fix

Author: lucia-sb

ddev/changelog.d/21340.added

@@ -0,0 +1 @@
+Adds a new method `merge_base` in the `GitRepository` class. 

ddev/src/ddev/utils/git.py

@@ -125,6 +125,9 @@ def capture(self, *args):
 
         return process.stdout
 
+    def merge_base(self, ref_a: str, ref_b: str | None = "HEAD") -> str:
+        return self.capture('merge-base', ref_a, ref_b).splitlines()[0]
+
     @staticmethod
     def __is_warning_line(line):
         return line.startswith('warning: ') or 'original line endings' in line

ddev/tests/utils/test_git.py

@@ -103,3 +103,41 @@ def test_fetch_tags(repository, mocker):
             check=True,
         ),
     ]
+
+
+def test_get_merge_base(repository):
+    repo = Repository(repository.path.name, str(repository.path))
+    base_commit = repo.git.latest_commit()
+    repo.git.capture('checkout', '-b', 'test_merge_base')
+
+    (repo.path / 'test1.txt').touch()
+    repo.git.capture('add', '.')
+    repo.git.capture('commit', '-m', 'test1')
+
+    base = repo.git.merge_base('origin/master')
+
+    assert base == base_commit.sha
+
+
+def test_get_merge_base_two_branches(repository):
+    repo = Repository(repository.path.name, str(repository.path))
+    base_commit = repo.git.latest_commit()
+
+    repo.git.capture('checkout', '-b', 'test1_merge_base')
+
+    (repo.path / 'test1.txt').touch()
+    repo.git.capture('add', '.')
+    repo.git.capture('commit', '-m', 'test1')
+
+    repo.git.capture('branch', 'test2_merge_base')
+
+    (repo.path / 'test1_1.txt').touch()
+    repo.git.capture('add', '.')
+    repo.git.capture('commit', '-m', 'test1_1')
+
+    repo.git.capture('checkout', 'test2_merge_base')
+    (repo.path / 'test2_1.txt').touch()
+    repo.git.capture('add', '.')
+    repo.git.capture('commit', '-m', 'test2')
+    base = repo.git.merge_base('origin/master')
+    assert base == base_commit.sha