TEST_CASE("std::optional") was guarded by #if !JSON_USE_IMPLICIT_CONVERSIONS,
so it only ever compiled in the non-default build with implicit conversions
disabled. This traces back to commit 1d7688aef (fixes#3859), which changed a
previously dead #ifndef JSON_USE_IMPLICIT_CONVERSIONS guard (the macro is
always defined by that point, so it never held) to #if !JSON_USE_IMPLICIT_CONVERSIONS
-- making the test compile for the first time, but only in the disabled-conversions
build. As a result, std::optional support had zero test coverage in the default
configuration almost every user builds with.
Verified the entire test case (all sections: null, string, bool, number, array,
object) compiles and passes identically with JSON_USE_IMPLICIT_CONVERSIONS both
on (default) and off -- nothing in it actually depends on the setting. Removing
the guard closes the coverage gap with no behavior change: 285 assertions pass
with implicit conversions on, 232 with them off (the difference comes from
other, unrelated conditionally-compiled tests in this file).
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
ae2182cce1