jyknight added a comment.

Ah -- I now understand your concern, and managing user expectations 
appropriately does seem like a potential concern.

I did not look too closely before into what exactly GCC categorized as 
"permerror" (errors that can be disabled with -fpermissive) vs what Clang 
categorized as "ExtWarn,DefaultError" diagnostics. Looking into it a little 
more now, I think there may not actually be substantial overlap between the two 
right now.

Many errors we have warning flags for are unconditional in GCC, and many that 
gcc allows disabling with -fpermissive are unconditional errors in clang.

You gave examples of the latter already, and e.g. here's a bunch of bogus code 
which you can currently build with -Wno-everything in clang, but most of which 
cannot be disabled in gcc (and I believe most if not all of these flags are 
ExtWarn, so would be disabled by this proposed -fpermissive):
https://godbolt.org/z/81NkJQ

Given that, yeah, it may not actually make sense to call this behavior 
-fpermissive.

I also can't really tell what the intent is behind classifying some diagnostics 
in Clang as ExtWarn,DefaultError and others Warning,DefaultError -- or if there 
even is any useful purpose there at all. I note with special-puzzlement the 
existence of both `ext_return_missing_expr` and `warn_return_missing_expr`.

I guess my feeling now is that perhaps we should just eliminate that 
categorization as meaningless, and just make -Wno-error=everything work 
properly (for anyone who wants to not abort the compile on broken code, but for 
whatever reason also loves to see build-spam so doesn't want -Wno-everything).


Repository:
  rC Clang

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D58154/new/

https://reviews.llvm.org/D58154



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