Export a make_linter_from_xpath() helper?

[MichaelChirico]

We have an unexported make_linter_from_regex() helper:

lintr/R/make_linter_from_regex.R

Line 1 in f8bb91e

make_linter_from_regex <- function(regex,

But that's only good for regex-based logic, which has a lot of pitfalls as we've learned.

Today I found myself trying to do some quick ad-hoc linting of a codebase and it was made more painful by the need to remember all the boilerplate for constructing a linter:

linter <- Linter(function(source_expression) {
   if (!is_lint_level(source_expression, $<LEVEL>)) return(list)
   xml <- source_expression$full_xml_parsed_content
   expr <- xml_find_all(xml, $<XPATH>)
   xml_nodes_to_lints(expr, source_expression, $<MESSAGE>, $<TYPE>)
 })

We could offer a helper to quickly generate a compliant linter function given an XPath. Proposed workflow:

new_linter <- make_linter_from_xpath($<XPATH>) # reasonable defaults for everything, including $<MESSAGE>
lint_dir(linters = new_linter)

In fact we could probably use that helper to generate many of our own linters.