Hi Guix! A question came up on IRC asking how to install package foo if and only if foo has a substitute available on any server (in this case, foo may be something like a web browser). This is different from the behavior of --fallback. From [1]:
> Note that when substitutes are disabled or no substitute is available > for the derivation in question, a local build will _always_ be > performed, regardless of whether or not ‘--fallback’ was given. The solution I came up with is "$ guix weather foo && guix install foo". However, this unfortunately does not work with how guix weather reports command success. Guix Weather returns nonzero if /any/ substitute server is missing the substitute, not just one. This hurts the ability to use guix weather in the context I described since false-negatives in substitute availability are detected. In my opinion "returning zero if any substitute server has foo available" is more useful behavior than "returning zero if and only if every substitute server has foo". I propose adding a --strict flag or similar to Guix weather. By default, Guix weather returns zero if any server has a substitute. With --strict, the current behavior is used. Alternatively, a cleaner but potentially more involved solution may be adding a --only-substitutes or similar flag to all commands that can initiate builds. [1]: (info "(guix) Substitution Failure") -- Take it easy, Richard Sent Making my computer weirder one commit at a time.
