Captured block parameter not recognised when used inside macro about crystal HOT 2 OPEN

This is not exacty #7975. The variable is not declared within the macro. It's only used there.

But it seems to be a similar issue. The compiler determines whether a block argument is a caputered block depending on whether the variable is referenced in the method body. Apparently it cannot recognise it when inside a macro.
So this relates to #8764.

It's easy to work around by inserting an explicit reference to the block variable outside the macro.

def assert(cond, &err : -> String)
  err
  {% if flag?(:debug) %}
    raise err.call unless cond
  {% end %}
end

from crystal.

You probably want to use a macro here:

macro assert(cond, &)
  {% if flag?(:debug) %}
    raise {{yield}} unless {{cond}}
  {% end %}
end

Related: #4263

Otherwise this is essentially a duplicate of #7975

from crystal.