code_size_compare.py: clean up worktree in errors of subprocess

With this change, the program cleans up worktree in errors of
execution of subprocess.checkout. Additionally, the error log is
printed out for users.

Signed-off-by: Aditya Deshpande <aditya.deshpande@arm.com>
Signed-off-by: Yanray Wang <yanray.wang@arm.com>

scripts/code_size_compare.py

@@ -141,16 +141,20 @@ class CodeSizeComparison:
                  git_worktree_path, revision], cwd=self.repo_path,
                 stderr=subprocess.STDOUT
             )
+
         return git_worktree_path
 
     def _build_libraries(self, git_worktree_path):
         """Build libraries in the specified worktree."""
 
         my_environment = os.environ.copy()
-        subprocess.check_output(
-            self.make_command, env=my_environment, shell=True,
-            cwd=git_worktree_path, stderr=subprocess.STDOUT,
-        )
+        try:
+            subprocess.check_output(
+                self.make_command, env=my_environment, shell=True,
+                cwd=git_worktree_path, stderr=subprocess.STDOUT,
+            )
+        except subprocess.CalledProcessError as e:
+            self._handle_called_process_error(e, git_worktree_path)
 
     def _gen_code_size_csv(self, revision, git_worktree_path):
         """Generate code size csv file."""
@@ -241,6 +245,20 @@ class CodeSizeComparison:
         self._get_code_size_for_rev(self.new_rev)
         return self.compare_code_size()
 
+    def _handle_called_process_error(self, e: subprocess.CalledProcessError,
+                                     git_worktree_path):
+        """Handle a CalledProcessError and quit the program gracefully.
+        Remove any extra worktrees so that the script may be called again."""
+
+        # Tell the user what went wrong
+        print("The following command: {} failed and exited with code {}"
+              .format(e.cmd, e.returncode))
+        print("Process output:\n {}".format(str(e.output, "utf-8")))
+
+        # Quit gracefully by removing the existing worktree
+        self._remove_worktree(git_worktree_path)
+        sys.exit(-1)
+
 def main():
     parser = argparse.ArgumentParser(
         description=(