in 30e82a81, we add a contraint to the template parameter of
boost_test_print_type() to prevent it from being matched with
types which can be formatted with operator<<. but it failed to
work. we still have test failure reports like:
```
[Exception] - critical check ['s', 's', 't', '_', 'm', 'r', '.', 'i', 's', '_', 'e', 'n', 'd', '_', 'o', 'f', '_', 's', 't', 'r', 'e', 'a', 'm', '(', ')'] has failed
```
this is not what we expect. the reason is that we passed the template
parameters to the `has_left_shift` trait in the wrong order, see
https://live.boost.org/doc/libs/1_83_0/libs/type_traits/doc/html/boost_typetraits/reference/has_left_shift.html.
we should have passed the lhs of operator<< expression as first
parameter, and rhs the second.
so, in this change, we correct the type constraint by passing the
template parameter in the right order, now the error message looks
better, like:
```
test/boost/mutation_query_test.cc(110): error: in "test_partition_query_is_full": check !partition_slice_builder(*s) .with_range({}) .build() .is_full() has failed
```
it turns out boost::transformed_range<> is formattable with operator<<,
as it fulfills the constraints of `boost::has_left_shift<ostream, R>`,
but when printing it, the compiler fails when it tries to insert the
elements in the range to the output stream.
so, in order to workaround this issue, we add a specialization for
`boost::transformed_range<F, R`.
also, to improve the readability, we reimplement the `has_left_shift<>`
as a concept, so that it's obvious that we need to put both the output
stream as the first parameter.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#20233
ee19bbed05