use safe repo.get_head methods

aider/coders/base_coder.py

@@ -713,7 +713,7 @@ class Coder:
         self.shell_commands = []
 
         if self.repo:
-            self.commit_before_message.append(self.repo.get_head())
+            self.commit_before_message.append(self.repo.get_head_sha())
 
     def run(self, with_message=None, preproc=True):
         try:
@@ -1867,7 +1867,7 @@ class Coder:
     def show_undo_hint(self):
         if not self.commit_before_message:
             return
-        if self.commit_before_message[-1] != self.repo.get_head():
+        if self.commit_before_message[-1] != self.repo.get_head_sha():
             self.io.tool_output("You can use /undo to undo and discard each aider commit.")
 
     def dirty_commit(self):

aider/commands.py

@@ -420,8 +420,8 @@ class Commands:
             self.io.tool_error("No git repository found.")
             return
 
-        last_commit = self.coder.repo.repo.head.commit
-        if not last_commit.parents:
+        last_commit = self.coder.repo.get_head()
+        if last_commit and not last_commit.parents:
             self.io.tool_error("This is the first commit in the repository. Cannot undo.")
             return
 
@@ -461,8 +461,9 @@ class Commands:
                 )
                 return
 
-        last_commit_hash = self.coder.repo.repo.head.commit.hexsha[:7]
-        last_commit_message = self.coder.repo.repo.head.commit.message.strip()
+        last_commit_hash = self.coder.repo.get_head_sha(short=True)
+        last_commit_message = self.coder.repo.get_head_message("(unknown)")
+
         if last_commit_hash not in self.coder.aider_commit_hashes:
             self.io.tool_error("The last commit was not made by aider in this chat session.")
             self.io.tool_error(
@@ -481,8 +482,8 @@ class Commands:
         self.io.tool_output(f"Removed: {last_commit_hash} {last_commit_message}")
 
         # Get the current HEAD after undo
-        current_head_hash = self.coder.repo.repo.head.commit.hexsha[:7]
-        current_head_message = self.coder.repo.repo.head.commit.message.strip()
+        current_head_hash = self.coder.repo.get_head_sha(short=True)
+        current_head_message = self.coder.repo.get_head_message("(unknown)")
         self.io.tool_output(f"Now at:  {current_head_hash} {current_head_message}")
 
         if self.coder.main_model.send_undo_reply:
@@ -494,7 +495,7 @@ class Commands:
             self.io.tool_error("No git repository found.")
             return
 
-        current_head = self.coder.repo.get_head()
+        current_head = self.coder.repo.get_head_sha()
         if current_head is None:
             self.io.tool_error("Unable to get current commit. The repository might be empty.")
             return

aider/repo.py

@@ -3,6 +3,7 @@ import time
 from pathlib import Path, PurePosixPath
 
 import git
+import gitdb
 import pathspec
 
 from aider import prompts, utils
@@ -137,7 +138,7 @@ class GitRepo:
             os.environ["GIT_AUTHOR_NAME"] = committer_name
 
         self.repo.git.commit(cmd)
-        commit_hash = self.repo.head.commit.hexsha[:7]
+        commit_hash = self.get_head_sha(short=True)
         self.io.tool_output(f"Commit {commit_hash} {commit_message}", bold=True)
 
         # Restore the env
@@ -374,6 +375,20 @@ class GitRepo:
 
     def get_head(self):
         try:
-            return self.repo.head.commit.hexsha
-        except ValueError:
+            return self.repo.head.commit
+        except (ValueError, gitdb.exc.ODBError):
             return None
+
+    def get_head_sha(self, short=False):
+        commit = self.get_head()
+        if not commit:
+            return
+        if short:
+            return commit.hexsha[:7]
+        return commit.hexsha
+
+    def get_head_message(self, default=None):
+        commit = self.get_head()
+        if not commit:
+            return default
+        return commit.message