<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/59151>59151</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Confusing error reporting while parsing a nested pass pipeline
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            bug,
            mlir:core
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          shabalind
      </td>
    </tr>
</table>

<pre>
    I'm currently working on a project that invokes MLIR a pass pipeline using Python bindings:
```python
mypm = pm.PassManager.parse(f"""builtin.module(
    mypass1,
    func.func(mypass2,mypass3)
)""")
```
Somewhat surprisingly this pass pipeline is not valid according to the pipeline parser, it tells me to add `,` at the end after `func.func(...)`. At the same time if you do add that comma, it errors as well since there is no valid pass name after the comma. 

As a workaround I added a dummy pass that does nothing just to make it happy:
```python
mypm = pm.PassManager.parse(f"""builtin.module(
    mypass1,
    func.func(mypass2,mypass3),
    dummy-do-nothing-pass
)""")
```
It would be great if this was not necessary in the first place, and parser accepted the initial snippet right away.

</pre>
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