[Support] Modernize YAML traits with is_detected (NFC) (#156598)

This patch modernizes has_* YAML traits with is_detected.

The resulting code should be a lot more readable because all the
SFINAE logic is hidden behind is_detected.

One note about has_FlowTraits.  The original code uses a complex trick
to detect a member variable named "flow", intentionally triggering
ambiguity with "flow" in the two base classes.  I've simplified the
check down to:

  template <class U> using check = decltype(&U::flow);

without using SameType.  The use of SameType here would make the trait
unnecessarily complicated.

While I am at it, this patch switches to "static constexpr bool".

0 files changed, 0 insertions, 0 deletions