[clang] [Clang][Driver] New parameter allow-unrecognized-arguments (PR #162201)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> This is another attempt at fixing #108455. Please see the initial discussion in the following PR: #111453

Thanks for investigating fixes here!

> This parameter is used to suppress the `Unknown argument '...'` error that clang will emit whenever it encounters an unknown argument.

Personally, I'm not a big fan of having a command line option to control diagnostics of command line options. I think command line options are generally processed in a left-to-right order where the last flag "wins", which is kind of awkward with this design. e.g.,
`--allow-unrecognized-arguments --invalid` silencing the diagnostic but `--invalid --allow-unrecognized-arguments` not silencing the diagnostic. Processing the full command line to find `--allow-unrecognized-arguments` and then continuing to process the command line arguments is possible, but it begs the question of why that's not done for all options related to diagnostic output.

I think this probably should remain an error. Passing unknown inputs to the compiler and expecting to get a known output is a pretty big ask IMO. That said, maybe others have a different opinion.

> This is probably an error to make sure the user fixes it's mistake by either removing the argument or renaming it, but there are some cases where it's not possible to fix the issue. For instance, CMake now injects gcc-specific arguments in the clang-tidy command that breaks static-analysis (https://gitlab.kitware.com/cmake/cmake/-/issues/26283)

IMO, that's a CMake bug; adding an option we have to support forever to work around that behavior is not really ideal.

https://github.com/llvm/llvm-project/pull/162201