Rearrange error msgs and add section markers (Trac #11014).

This puts the "Relevant bindings" section at the end.

It uses a TcErrors.Report Monoid to divide messages by importance and
then mappends them together.  This is not the most efficient way since
there are various intermediate Reports and list appends, but it probably
doesn't matter since error messages shouldn't get that large, and are
usually prepended.  In practice, everything is `important` except
`relevantBindings`, which is `supplementary`.

ErrMsg's errMsgShortDoc and errMsgExtraInfo were extracted into ErrDoc,
which has important, context, and suppelementary fields.  Each of those
three sections is marked with a bullet character, '•' on unicode
terminals and '*' on ascii terminals.  Since this breaks tons of tests,
I also modified testlib.normalise_errmsg to strip out '•'s.

--- Additional notes:

To avoid prepending * to an empty doc, I needed to filter empty docs.
This seemed less error-prone than trying to modify everyone who produces
SDoc to instead produce Maybe SDoc.  So I added `Outputable.isEmpty`.
Unfortunately it needs a DynFlags, which is kind of bogus, but otherwise
I think I'd need another Empty case for SDoc, and then it couldn't be a
newtype any more.

ErrMsg's errMsgShortString is only used by the Show instance, which is
in turn only used by Show HscTypes.SourceError, which is in turn only
needed for the Exception instance.  So it's probably possible to get rid
of errMsgShortString, but that would a be an unrelated cleanup.

Fixes #11014.

Test Plan: see above

Reviewers: austin, simonpj, thomie, bgamari

Reviewed By: thomie, bgamari

Subscribers: simonpj, nomeata, thomie

Differential Revision: https://phabricator.haskell.org/D1427

GHC Trac Issues: #11014

1 files changed, 4 insertions, 4 deletions

diff --git a/testsuite/tests/arrows/should_fail/T5380.stderr b/testsuite/tests/arrows/should_fail/T5380.stderr
index bff48f5233..177183225c 100644
--- a/testsuite/tests/arrows/should_fail/T5380.stderr
+++ b/testsuite/tests/arrows/should_fail/T5380.stderr
@@ -5,12 +5,12 @@ T5380.hs:7:27:
                  the type signature for:
                  testB :: not_bool -> (() -> ()) -> () -> not_unit
                  at T5380.hs:6:10
+    In the expression: b
+    In the expression: proc () -> if b then f -< () else f -< ()
     Relevant bindings include
       b :: not_bool (bound at T5380.hs:7:7)
       testB :: not_bool -> (() -> ()) -> () -> not_unit
         (bound at T5380.hs:7:1)
-    In the expression: b
-    In the expression: proc () -> if b then f -< () else f -< ()
 
 T5380.hs:7:34:
     Couldn't match type ‘not_unit’ with ‘()’
@@ -20,8 +20,8 @@ T5380.hs:7:34:
                  at T5380.hs:6:10
     Expected type: () -> not_unit
       Actual type: () -> ()
+    In the expression: f
+    In the command: f -< ()
     Relevant bindings include
       testB :: not_bool -> (() -> ()) -> () -> not_unit
         (bound at T5380.hs:7:1)
-    In the expression: f
-    In the command: f -< ()