Is your feature request related to a problem? Please describe.

• I've tried to build my package, but an unrelated cache is failing

  building '/nix/store/8z0aq6pnim0v2rfnl97m5wqq505v3qaj-cabal2nix-.drv'...
  installing
  warning: unable to download 'https://my-self-hosted-unreliable-cache/1p34mip9xdfr5zp12895z7wxj9pgq83m.narinfo': HTTP error 502; retrying in 314 ms
  warning: unable to download 'https://my-self-hosted-unreliable-cache/1p34mip9xdfr5zp12895z7wxj9pgq83m.narinfo': HTTP error 502; retrying in 521 ms
  warning: unable to download 'https://my-self-hosted-unreliable-cache/1p34mip9xdfr5zp12895z7wxj9pgq83m.narinfo': HTTP error 502; retrying in 1390 ms
  warning: unable to download 'https://my-self-hosted-unreliable-cache/1p34mip9xdfr5zp12895z7wxj9pgq83m.narinfo': HTTP error 502; retrying in 2140 ms
  error: unable to download 'https://my-self-hosted-unreliable-cache/1p34mip9xdfr5zp12895z7wxj9pgq83m.narinfo': HTTP error 502
  

• I can realise what's happening and the obvious desired behavior is to disable that cache for this build but I don't know how to do that

• I have to go and hunt down --option substitute false, and then do a build with no caching at all

Describe the solution you'd like

Ideally nix could be configured to always treat cache errors as misses, this is almost always the behavior I want.

Failing that, the least it could do would be to print on stderr Looks like a cache is failing, perhaps you want '--option ignore-cache https://my-self-hosted-unreliable-cache/' (or even just prompt --option substitute false).