Improve error traceback

[cderv]

This PR follows up on evaluate 1.0.3 work.

• knitr does entrace all error with rlang when available. This is done now in the calling handler of evaluate, closest to the error being thrown

• evaluate does handle already trimming the backtrace for error thrown in the code evaluated. knitr need also to do it for error happening in its value handler passed to evaluate, and calling knit_print()

  • This is done at the knit_print() level directly; But it could be done also at the value handler
    

    knitr/R/utils.R

    Lines 882 to 887 in 8a37857

    	merge_list(default_handlers, list(
    	value = function(x, visible) {
    	if (visible) fun(x, options = options)
    	},
    	calling_handlers = c(options$calling.handlers, rlang_entrace_handler)
    	))

  • Or evaluate could also do it so that it happens for any value handler, including knitr's one.