Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

This patch adds the AsyncSource trait, the interface for providing async
source functionality for this crate.

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
Reviewed-by: Matthias Beyer <mail@beyermatthias.de>

This patch rewrites the Config building mechanism using special objects
for tracking the config building state.

Transitions between states are done on the fly as required.

This is required so that the async sources can be stored inside the
configuration building objects, while keeping out the expenses in the
non-async case, so a user of the crate has only to pay for what they are
using (no async means no overhead for that).

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
Reviewed-by: Matthias Beyer <mail@beyermatthias.de>

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
Reviewed-by: Matthias Beyer <mail@beyermatthias.de>

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
Reviewed-by: Matthias Beyer <mail@beyermatthias.de>

This is required because the examples pull in the "reqwest" crate, which
depends on "socket2" and this crate fails to build if the "const fn"
feature is not present (which wasn't on 1.44.0).

Hence, we only run the tests in the 1.44.0 job, but do not compile the
examples.

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

Because one of our dependencies (namingly `socket2`) uses match in a
const fn, which is stabilized in rust 1.46.0, we bump to this version as
MSRV for this crate.

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
Tested-by: Matthias Beyer <mail@beyermatthias.de>

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

With this simplification, we save a bit of code on one side, but also
showcase that errors from custom AsyncSource implementations are
possible because the ConfigError type provides a variant for it.

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
Tested-by: Matthias Beyer <mail@beyermatthias.de>