Multiline Problem Matcher

[smorimoto]

In #319 there was a discussion about the multiline "problem matcher" which was closed even though it was not actually fixed on the problem matcher side, so I think it's time to have this discussion again.

For example, OCaml has the following error log, which is very difficult to catch with current problem matcher.

File "bin/main.ml", line 0, characters 0-0:
type t =
  | Foo of string [@ocaml.warn_on_literal_pattern]
  | Bar of string

let no_warning = function
  | Bar "specific value" -> 0
  | _ -> 1

let warning = function
  | Foo "specific value" -> 0
  | _ -> 1
Warning 52 [fragile-literal-pattern]: Code should not depend on the actual values of
this constructor's arguments. They are only for information
and may change in future versions. (See manual section 13.5)

In such a case, it would be a fairly complex regular expression, but you can catch properly with code like the following, but the current implementation just works line-by-line.

^File\s"(.+)",\sline\s(\d+),\scharacters\s(\d+)-(\d+):\n((.|\n)+?)(Error|Warning)\s*(.*):\s((.|\n(?!File\s))+)$

https://regex101.com/r/gP6PEM/1

This means that it's impossible to matching such logs with such a regular expression.
In other words, we can't deal with issues like #319 on the user's end. Do you have any improvement plans for this?

[Emilgardis]

In such a case, it would be a fairly complex regular expression, but you can catch properly with code like the following, but the current implementation just works line-by-line.

That is, the current problem matcher regexp field does not allow this complex regular expression, because the expression assumes that ., [\S\s] and \n works across multiple lines, but the regexp only matches per line.

It's possible to use loop to go across multiple lines with different errors, but it's not possible to capture a multi-line error message using that strategy.

[smorimoto]

Yes, that is exactly the problem. It is hard to understand why the GitHub Actions problem matcher is designed this way 🤷‍♂️

[smorimoto]

@joshmgross @dhadka @chrispat @bryanmacfarlane @TingluoHuang Any thoughts on this? Or could you route this topic to the appropriate people?