ensures that surf can build as much as possible without an enabled client. This is important in use cases where someone is providing their own HttpClient backend, as supported by surf features.
simplifies the logic for checking if there's a client by adding a "default-client" feature that's enabled by all of the other clients. This will simplify addition of future client backends.
introduces the use of cfg_if, in order to make the mutually-exclusive conditional logic more clear.
Not covered by this PR: Considering what happens if someone enables multiple backends.
There are exactly two places that panic in this PR that would not have panicked otherwise. We could return a custom error if that's preferred, although it seems like "trying to send a request without a default client backend and without an explicitly configured http_client" is exactly the sort of developer-caused error scenario that panics are ideal for. This also should be a fairly rare condition, because anyone using surf without default features likely understands that they can't rely on a default client.
This PR:
Not covered by this PR: Considering what happens if someone enables multiple backends.
There are exactly two places that panic in this PR that would not have panicked otherwise. We could return a custom error if that's preferred, although it seems like "trying to send a request without a default client backend and without an explicitly configured http_client" is exactly the sort of developer-caused error scenario that panics are ideal for. This also should be a fairly rare condition, because anyone using surf without default features likely understands that they can't rely on a default client.