Avi Kivity fb5664a1d5 interval: split interval_bound implementation for const references ...

In f3dccc2215 ("interval: change start()/end() not to return
references to data members"), we introduced interval_bound_const_ref
as a lightweight alternative to interval_bound that does not carry
a T. This was needed because interval no longer contains
interval_bound:s.

This interval_bound_const_ref was just an interval_bound<const T&>,
and converting constructors and operators were added to move between
the interval_bound<T> and interval_bound<const T&>.

However, these happen to be illegal in C++ and just happened to work
in clang 20. Clang 21 tightened its checks and these are now flagged.
The problem is that when instantiating interval_bound<const T&> the
converting constructor looks like a copy constructor; and while it's
behind a constraint (that evaluates to false) the rules don't care
about that.

Fix this by having a separate interval_bound_const_ref template.
The new template is slightly better as it allows assignment (since
the payload is a pointer rather than a reference). Not that it's really
needed.

The C++ rule was reported [1] as too restrictive, but there is no
resolution yet.

[1] https://cplusplus.github.io/CWG/issues/2837.html

Closes scylladb/scylladb#26081

2025-09-24 13:57:21 +02:00

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