Because downstream code expects to use `==` on platform attrsets, we
are unfortunately not able to throw a useful error message when the
`sharedLibrary` attribute is accessed.
When users do a comparison like:
stdenv.hostPlatform == pkgsStatic.stdenv.hostPlatform
... in a situation where `stdenv.hostPlatform.hasSharedLibraries`,
they expect this to return `false`. Unfortunately Nix does a deep
equality comparison here, and ends up forcing the
`pkgsStatic.stdenv.hostPlatform.extensions.sharedLibrary` attribute,
which throws the error.
Rather than returning `null`, this commit instead simply omits the
`extensions.sharedLibrary` attribute. This provides the user with a
more-useful error message: instead of waiting until the `null` is
used (and hoping that produces an error), the user will get an error
about the `extensions.sharedLibrary` attribute being missing, at the
position where it was referenced.
Big thanks to @trofi for his PR to add
`NIX_VALIDATE_EVAL_NONDETERMINISM` to Nix, which I am now using. It
made tracking this down really easy!
Fixes#244045
d278fd78af