fix: better detect merge-commits (#397)

Apparently a common thing for CIs to do is create a merge-commit for changes
in a branch before running tests and stuff.
This means that - especially for not-directly-supported CIs - we would maybe
return a SHA for a commit that didn't exist in the branch.

These changes fix that by checking to see if the current commit is a merge commit.
If it is we return the second parent, the most recent commit before the current one.

Q: What if the current latest commit in the branch is a merge commit?
Well in this case the parent, which is also part of the branch, will have the coverage.

Users can still provide a commit sha value to override this behavior.

closes #372

codecov_cli/helpers/versioning_systems.py

@@ -42,6 +42,20 @@ def is_available(cls):
 
     def get_fallback_value(self, fallback_field: FallbackFieldEnum):
         if fallback_field == FallbackFieldEnum.commit_sha:
+            # here we will get the commit SHA of the latest commit
+            # that is NOT a merge commit
+            p = subprocess.run(
+                # List current commit parent's SHA
+                ["git", "rev-parse", "HEAD^@"],
+                capture_output=True,
+            )
+            parents_hash = p.stdout.decode().strip().splitlines()
+            if len(parents_hash) == 2:
+                # IFF the current commit is a merge commit it will have 2 parents
+                # We return the 2nd one - The commit that came from the branch merged into ours
+                return parents_hash[1]
+            # At this point we know the current commit is not a merge commit
+            # so we get it's SHA and return that
             p = subprocess.run(["git", "log", "-1", "--format=%H"], capture_output=True)
             if p.stdout:
                 return p.stdout.decode().strip()
@@ -56,7 +70,7 @@ def get_fallback_value(self, fallback_field: FallbackFieldEnum):
                 return branch_name if branch_name != "HEAD" else None
 
         if fallback_field == FallbackFieldEnum.slug:
-            # if there are multiple remotes, we will prioritize using the one called 'origin' if it exsits, else we will use the first one in 'git remote' list
+            # if there are multiple remotes, we will prioritize using the one called 'origin' if it exists, else we will use the first one in 'git remote' list
 
             p = subprocess.run(["git", "remote"], capture_output=True)
 
@@ -78,7 +92,7 @@ def get_fallback_value(self, fallback_field: FallbackFieldEnum):
             return parse_slug(remote_url)
 
         if fallback_field == FallbackFieldEnum.git_service:
-            # if there are multiple remotes, we will prioritize using the one called 'origin' if it exsits, else we will use the first one in 'git remote' list
+            # if there are multiple remotes, we will prioritize using the one called 'origin' if it exists, else we will use the first one in 'git remote' list
 
             p = subprocess.run(["git", "remote"], capture_output=True)
             if not p.stdout:

tests/helpers/test_versioning_systems.py

@@ -8,17 +8,28 @@
 
 class TestGitVersioningSystem(object):
     @pytest.mark.parametrize(
-        "commit_sha,expected", [("", None), (b" random_sha  ", "random_sha")]
+        "runs_output,expected",
+        [
+            # No output for parents nor commit
+            ([b"", b""], None),
+            # No output for parents, commit has SHA
+            ([b"", b" random_sha"], "random_sha"),
+            # Commit is NOT a merge-commit
+            ([b" parent_sha", b" random_sha  "], "random_sha"),
+            # Commit IS a merge-commit
+            ([b" parent_sha0\nparent_sha1", b" random_sha"], "parent_sha1"),
+        ],
     )
-    def test_commit_sha(self, mocker, commit_sha, expected):
-        mocked_subprocess = MagicMock()
+    def test_commit_sha(self, mocker, runs_output, expected):
+        mocked_subprocess = [
+            MagicMock(**{"stdout": runs_output[0]}),
+            MagicMock(**{"stdout": runs_output[1]}),
+        ]
         mocker.patch(
             "codecov_cli.helpers.versioning_systems.subprocess.run",
-            return_value=mocked_subprocess,
+            side_effect=mocked_subprocess,
         )
 
-        mocked_subprocess.stdout = commit_sha
-
         assert (
             GitVersioningSystem().get_fallback_value(FallbackFieldEnum.commit_sha)
             == expected

tests/services/upload/test_coverage_file_finder.py

@@ -295,7 +295,9 @@ def test_find_coverage_files_with_user_specified_files_not_found(self):
         expected_paths = sorted([file.get_filename() for file in expected])
         self.assertEqual(result, expected_paths)
 
-    def test_find_coverage_files_with_user_specified_files_in_default_ignored_folder(self):
+    def test_find_coverage_files_with_user_specified_files_in_default_ignored_folder(
+        self,
+    ):
         # Create some sample coverage files
         coverage_files = [
             self.project_root / "coverage.xml",