I'd suspect it's your boot compiler producing that error, and that what changed might have been the file being compiled, causing a recompile with the wrong compiler? On Wed, Mar 25, 2026 at 8:53 AM Simon Peyton Jones via ghc-devs < ghc-devs@haskell.org> wrote:
Friends
After 10 days of working on !15719 I have suddenly started getting
/home/simonpj/code/HEAD-19/libraries/ghc-boot-th-next/../ghc-internal/src/GHC/Internal/Classes.hs:10:17: error: [GHC-04924] Unknown flag in {-# OPTIONS_GHC #-} pragma: -fdefines-known-key-names | 10 | {-# OPTIONS_GHC -fdefines-known-key-names #-} | ^^^^^^^^^^^^^^^^^^^^^^^^^
I have no idea why this was fine until 10am this morning, and has suddenly started happening now.
*How does GHC decide what runtime flags it allows? * `-fdefines-known-key-names` is in GHC.Driver.Session.fFlagsDeps.
I'm boggled that it worked until 10am and then abruptly stopped.
Any advice?
Simon
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