Improved compile messages about rebar3 HOT 4 OPEN

What we have in eqwalizer is actually not available in regular Erlang. We not only have line + column, but we actually have full start/end range for every construct in AST (the price is that the AST format is not backwards compatible). This allows the reported ranges to be precise, rather than just the single point information that Erlang compiler has - that said, this is still better than just line information.

from rebar3.

This isn't really hard and I wanted to give it a try for a partial implementation to see the style, it looks like this so far:

-module(rebar_fake).

-export([diagnostic/1]).

diagnostic(A) ->
    X = add(5 / 0),
    {X,X}.

add(X) -> X.

add(X, Y) -> X + Y.

Calling rebar3 escriptize:

...
===> Compiling rebar
===> Compiling apps/rebar/src/rebar_fake.erl failed
apps/rebar/src/rebar_fake.erl:5:12:
  diagnostic(A) ->
             ^-- variable 'A' is unused
apps/rebar/src/rebar_fake.erl:6:15:
      X = add(5 / 0),
                ^-- evaluation of operator '/'/2 will fail with a 'badarith' exception
apps/rebar/src/rebar_fake.erl:11:1:
  add(X, Y) -> X + Y.
  ^-- function add/2 is unused

Seems to be okay-ish.

See #2783

from rebar3.

(this draft PR is likely to look like garbage on errors on long long lines I guess, but it shows a very easy way to get improvements)

from rebar3.

Ah, I thought it did the range based on the error itself. Like if the error says there is an issue at when then you know to highlight the whole when.

from rebar3.