<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/139218>139218</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Bazel] `@llvm-project//llvm:Support` fails to build due to incomplete `DelimitedScope`
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          hankhsu1996
      </td>
    </tr>
</table>

<pre>
    When using `@llvm-project//llvm:Support` in a Bazel project, the build fails because `DelimitedScope` is forward-declared in `ScopedPrinter.h` but never defined. This causes `sizeof(DelimitedScope)` to trigger a compilation error when the compiler instantiates `std::unique_ptr<DelimitedScope>`.

Reproduce:

1. Add `@llvm-project//llvm:Support` as a dependency in a `cc_library`.
2. Include `<llvm/Support/Allocator.h>` (which transitively pulls in `ScopedPrinter.h`).
3. Build with Clang or GCC.

Observed error:

```
error: invalid application of 'sizeof' to an incomplete type 'llvm::DelimitedScope'
```

This blocks downstream projects from using `Support` safely.

Suggested fix: either define `DelimitedScope`, or remove it from the public headers until complete.

</pre>
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