[clang] [clang-format] Add --fail-on-incomplete-format. (PR #84346)

[Roberto Bampi via cfe-commits]

gigaroby wrote:

I think the documentation failure is related to https://github.com/llvm/llvm-project/commit/0c423af59c971ddf1aa12d94529edf8293608157 but I might be wrong.

https://github.com/llvm/llvm-project/pull/84346