Commits on Sep 15, 2024

1. llvmPackages.*: Add devExtraCmakeFlags parameter …

   cmake flags have a 'last flag wins' logic, so by appending to the end of
   the flags it is possible to override any cmake flag.
   
   It also ignores (and warns) if a flag is unused, so passing flags across
   all packages should be safe if you want to target one package.
   
   In combination with NixOS#320261, this PR allows consistently overriding all
   packages within LLVM with additional cmake arguments. Consistency here
   means for example 'if you override LLVM, then all dependencies on it are
   also see the overridden LLVM in their input'. Consistency is hard to
   achieve with the other obvious way of implementing this as a user: if
   you use overrideAttrs then you have to write a big mess of override code
   in order to override all dependents, and this can be very difficult in a
   cross-compilation scenario using crossSystem and useLLVM, for example.
   
   With this PR it is possible to write an overlay which overlays
   `llvmPackages` with `llvmPackage.override { devExtraCmakeFlags = [ ... ]; }`,
   and then the toolchain used with useLLVM in effect should respect
   these flags.
   
   This is useful in development for experimenting with the effect of
   various flags, hence the chosen name `devCmakeFlags`.
   
   This won't work out of the box without NixOS#341855 applied, which fixes
   override passthrough.
   
   See-Also: NixOS#320261, NixOS#341855
   Signed-off-by: Peter Waller <[email protected]>

   

   pwaller committed Sep 15, 2024
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