aider: Modify run_cmd method to capture both stdout and stderr together using subprocess.Popen.

# Aider chat conversation:

USER: can `check_output` intermingle stdout and stdin like they would be in a terminal?

ASSISTANT: The `subprocess.check_output` function captures the output of the command and returns it as a string. It does not intermingle stdout and stderr like they would be in a terminal. If you need to capture both stdout and stderr together, you can use `subprocess.Popen` with `stdout=subprocess.PIPE` and `stderr=subprocess.STDOUT`.

Would you like me to modify the `run_cmd` method to use `subprocess.Popen` to capture both stdout and stderr together?

USER: yes

ASSISTANT: Here are the changes to modify the `run_cmd` method to use `subprocess.Popen` to capture both stdout and stderr together:

aider/linter.py
```python
<<<<<<< SEARCH
        try:
            subprocess.check_output(cmd, cwd=self.root).decode()
            return  # zero exit status
        except subprocess.CalledProcessError as err:
            errors = err.output.decode()  # non-zero exit status
=======
        process = subprocess.Popen(cmd, cwd=self.root, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
        stdout, _ = process.communicate()
        errors = stdout.decode()
        if process.returncode == 0:
            return  # zero exit status
>>>>>>> REPLACE
```

This change ensures that both stdout and stderr are captured together, similar to how they would be intermingled in a terminal.

aider/linter.py

@@ -38,11 +38,13 @@ class Linter:
         cmd += " " + rel_fname
         cmd = cmd.split()
 
-        try:
-            subprocess.check_output(cmd, cwd=self.root).decode()
+        process = subprocess.Popen(
+            cmd, cwd=self.root, stdout=subprocess.PIPE, stderr=subprocess.STDOUT
+        )
+        stdout, _ = process.communicate()
+        errors = stdout.decode()
+        if process.returncode == 0:
             return  # zero exit status
-        except subprocess.CalledProcessError as err:
-            errors = err.output.decode()  # non-zero exit status
 
         cmd = " ".join(cmd)
         res = f"# Running: {cmd}\n\n"