Mention which -Werror promoted a warning to an error

Previously -Werror or -Werror=flag printed warnings as usual and then
printed
these two lines:

    <no location info>: error:
    Failing due to -Werror.

This is not ideal: first, it's not clear which flag made one of the
warnings an
error. Second, warning messages are not modified in any way, so there's
no way
to know which warnings caused this error.

With this patch we (1) promote warning messages to error messages if a
relevant
-Werror is enabled (2) mention which -Werror is used during this
promotion.

Previously:

    [1 of 1] Compiling Main             ( test.hs, test.o )

    test.hs:9:10: warning: [-Wincomplete-patterns]
        Pattern match(es) are non-exhaustive
        In a case alternative: Patterns not matched: (C2 _)
      |
    9 | sInt s = case s of
      |          ^^^^^^^^^...

    test.hs:12:14: warning: [-Wmissing-fields]
        • Fields of ‘Rec’ not initialised: f2
        • In the first argument of ‘print’, namely ‘Rec {f1 =
1}’
          In the expression: print Rec {f1 = 1}
          In an equation for ‘main’: main = print Rec {f1 = 1}
       |
    12 | main = print Rec{ f1 = 1 }
       |              ^^^^^^^^^^^^^

    <no location info>: error:
    Failing due to -Werror.

Now:

    [1 of 1] Compiling Main             ( test.hs, test.o )

    test.hs:9:10: error: [-Wincomplete-patterns,
-Werror=incomplete-patterns]
        Pattern match(es) are non-exhaustive
        In a case alternative: Patterns not matched: (C2 _)
      |
    9 | sInt s = case s of
      |          ^^^^^^^^^...

    test.hs:12:14: error: [-Wmissing-fields, -Werror=missing-fields]
        • Fields of ‘Rec’ not initialised: f2
        • In the first argument of ‘print’, namely ‘Rec {f1 =
1}’
          In the expression: print Rec {f1 = 1}
          In an equation for ‘main’: main = print Rec {f1 = 1}
       |
    12 | main = print Rec{ f1 = 1 }
       |              ^^^^^^^^^^^^^

Test Plan: - Update old tests, add new tests if there aren't any
relevant tests

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3709

1 files changed, 8 insertions, 11 deletions

diff --git a/testsuite/tests/driver/werror.stderr b/testsuite/tests/driver/werror.stderr
index ccbeb393cd..2d9fd5324c 100644
--- a/testsuite/tests/driver/werror.stderr
+++ b/testsuite/tests/driver/werror.stderr
@@ -1,31 +1,28 @@
 
-werror.hs:6:1: warning: [-Wmissing-signatures (in -Wall)]
+werror.hs:6:1: error: [-Wmissing-signatures (in -Wall), -Werror=missing-signatures]
     Top-level binding with no type signature: main :: IO ()
 
-werror.hs:7:13: warning: [-Wname-shadowing (in -Wall)]
+werror.hs:7:13: error: [-Wname-shadowing (in -Wall), -Werror=name-shadowing]
     This binding for ‘main’ shadows the existing binding
       defined at werror.hs:6:1
 
-werror.hs:7:13: warning: [-Wunused-local-binds (in -Wextra, -Wunused-binds)]
+werror.hs:7:13: error: [-Wunused-local-binds (in -Wextra, -Wunused-binds), -Werror=unused-local-binds]
     Defined but not used: ‘main’
 
-werror.hs:8:1: warning: [-Wtabs (in -Wdefault)]
+werror.hs:8:1: error: [-Wtabs (in -Wdefault), -Werror=tabs]
     Tab character found here.
     Please use spaces instead.
 
-werror.hs:10:1: warning: [-Wunused-top-binds (in -Wextra, -Wunused-binds)]
+werror.hs:10:1: error: [-Wunused-top-binds (in -Wextra, -Wunused-binds), -Werror=unused-top-binds]
     Defined but not used: ‘f’
 
-werror.hs:10:1: warning: [-Wmissing-signatures (in -Wall)]
+werror.hs:10:1: error: [-Wmissing-signatures (in -Wall), -Werror=missing-signatures]
     Top-level binding with no type signature: f :: [a1] -> [a2]
 
-werror.hs:10:1: warning: [-Wincomplete-patterns (in -Wextra)]
+werror.hs:10:1: error: [-Wincomplete-patterns (in -Wextra), -Werror=incomplete-patterns]
     Pattern match(es) are non-exhaustive
     In an equation for ‘f’: Patterns not matched: (_:_)
 
-werror.hs:11:1: warning: [-Woverlapping-patterns (in -Wdefault)]
+werror.hs:11:1: error: [-Woverlapping-patterns (in -Wdefault), -Werror=overlapping-patterns]
     Pattern match is redundant
     In an equation for ‘f’: f [] = ...
-
-<no location info>: error: 
-Failing due to -Werror.