Fix text diff for 1st commit and deleted files

jupyterlab_git/git.py

@@ -1085,6 +1085,7 @@ async def show(self, filename, ref, top_repo_path):
                 "fatal: Path '{}' does not exist (neither on disk nor in the index)".format(
                     filename
                 ),
+                "fatal: Path '{}' does not exist in '{}'".format(filename, ref),
             ],
         )
         lower_error = error.lower()
@@ -1104,20 +1105,34 @@ def get_content(self, filename, top_repo_path):
         Get the file content of filename.
         """
         relative_repo = os.path.relpath(top_repo_path, self.root_dir)
-        model = self.contents_manager.get(path=os.path.join(relative_repo, filename))
+        try:
+            model = self.contents_manager.get(
+                path=os.path.join(relative_repo, filename)
+            )
+        except tornado.web.HTTPError as error:
+            # Handle versioned file being deleted case
+            if error.status_code == 404 and error.log_message.startswith(
+                "No such file or directory: "
+            ):
+                return ""
+            raise error
         return model["content"]
 
     async def diff_content(self, filename, prev_ref, curr_ref, top_repo_path):
         """
         Collect get content of prev and curr and return.
         """
-        is_binary = await self._is_binary(filename, prev_ref["git"], top_repo_path)
-        if is_binary:
-            raise tornado.web.HTTPError(
-                log_message="Error occurred while executing command to retrieve plaintext diff as file is not UTF-8."
-            )
+        if prev_ref["git"]:
+            is_binary = await self._is_binary(filename, prev_ref["git"], top_repo_path)
+            if is_binary:
+                raise tornado.web.HTTPError(
+                    log_message="Error occurred while executing command to retrieve plaintext diff as file is not UTF-8."
+                )
+
+            prev_content = await self.show(filename, prev_ref["git"], top_repo_path)
+        else:
+            prev_content = ""
 
-        prev_content = await self.show(filename, prev_ref["git"], top_repo_path)
         if "special" in curr_ref:
             if curr_ref["special"] == "WORKING":
                 curr_content = self.get_content(filename, top_repo_path)

jupyterlab_git/tests/test_handlers.py

@@ -679,7 +679,7 @@ def test_diffcontent_show_unhandled_error(self, mock_execute):
             self.tester.post(["diffcontent"], body=body)
 
     @patch("jupyterlab_git.git.execute")
-    def test_diffcontent_getcontent_error(self, mock_execute):
+    def test_diffcontent_getcontent_deleted_file(self, mock_execute):
         # Given
         top_repo_path = "path/to/repo"
         filename = "my/absent_file"
@@ -688,7 +688,6 @@ def test_diffcontent_getcontent_error(self, mock_execute):
         mock_execute.side_effect = [
             maybe_future((0, "1\t1\t{}".format(filename), "")),
             maybe_future((0, content, "")),
-            maybe_future((0, content, "")),
         ]
 
         # When
@@ -699,5 +698,18 @@ def test_diffcontent_getcontent_error(self, mock_execute):
             "top_repo_path": top_repo_path,
         }
         # Then
-        with assert_http_error(404, msg="No such file or directory"):
-            self.tester.post(["diffcontent"], body=body)
+        response = self.tester.post(["diffcontent"], body=body)
+
+        # Then
+        assert response.status_code == 200
+        payload = response.json()
+        assert payload["prev_content"] == content
+        assert payload["curr_content"] == ""
+        mock_execute.assert_has_calls(
+            [
+                call(
+                    ["git", "show", "{}:{}".format("previous", filename)],
+                    cwd=os.path.join(self.notebook_dir, top_repo_path),
+                )
+            ]
+        )