Safe logging macros don't work in generated functions due to with_logger closure

[danielwe]

This is my fault, ref #622

MWE:

julia> using GPUCompiler

julia> @generated function trywarn()
           return :(GPUCompiler.@safe_warn "watch out!")
       end
trywarn (generic function with 1 method)

julia> trywarn()
ERROR: The function body AST defined by this @generated function is not pure. This likely means it contains a closure, a comprehension or a generator.
Stacktrace:
 [1] top-level scope
   @ REPL[5]:1

The problem is there's no public closure-free API to change the current logger. The non-public way is to reassign current_task().logstate, which is what with_logger does under the hood.

So I guess the choices are

• Copy the internals of with_logger, i.e., reassign the non-public current_task().logstate
• Revert to mutating the global logger and hope that @safe_* is never used in a task that's attached to a non-global logger