[GHC] #10021: Add "Error:" prefix for error-messages

[GHC]

#10021: Add "Error:" prefix for error-messages
-------------------------------------+-------------------------------------
        Reporter:  k-bx              |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
Description changed by k-bx:

Old description:

> Similar to what we have for "Warning:".
>
> E.g., we have:
>
> {{{
> ➜ cat test.hs
> main = putStrLn "Hello!"
> ➜ ghc --make -fforce-recomp -Wall ./test.hs
> [1 of 1] Compiling Main             ( test.hs, test.o )
>
> test.hs:1:1: Warning:
>     Top-level binding with no type signature: main :: IO ()
> Linking test ...
> ➜ cat test2.hs
> main = foo
> ➜ ghc --make -fforce-recomp -Wall ./test2.hs
> [1 of 1] Compiling Main             ( test2.hs, test2.o )
>
> test2.hs:1:8: Not in scope: ‘foo’
> }}}
>
> And I propose having:
>
> {{{
> ➜ cat test2.hs
> main = foo
> ➜ ghc --make -fforce-recomp -Wall ./test2.hs
> [1 of 1] Compiling Main             ( test2.hs, test2.o )
>
> test2.hs:1:8: Error: Not in scope: ‘foo’
> }}}

New description:

 Similar to what we have for "Warning:".

 E.g., we have:

 {{{
 ➜ cat test.hs
 main = putStrLn "Hello!"
 ➜ ghc --make -fforce-recomp -Wall ./test.hs
 [1 of 1] Compiling Main             ( test.hs, test.o )

 test.hs:1:1: Warning:
     Top-level binding with no type signature: main :: IO ()
 Linking test ...
 ➜ cat test2.hs
 main = foo
 ➜ ghc --make -fforce-recomp -Wall ./test2.hs
 [1 of 1] Compiling Main             ( test2.hs, test2.o )

 test2.hs:1:8: Not in scope: ‘foo’
 }}}

 And I propose having:

 {{{
 ➜ cat test2.hs
 main = foo
 ➜ ghc --make -fforce-recomp -Wall ./test2.hs
 [1 of 1] Compiling Main             ( test2.hs, test2.o )

 test2.hs:1:8: Error: Not in scope: ‘foo’
 }}}


 == Motivation ==

 Main motivation point right now is that there's a ticket #9219 (parallel
 build's output of errors doesn't occur at the end of output), due to
 which, error-reporting of your program might get lost somewhere in the
 middle of a build-log. As another example, if your program has a lot of
 warnings, and you build it with multiple cores, you almost always get an
 error lost somewhere in the middle of warnings and it's almost impossible
 to find.

 So, this feature's main purpose is to ease navigation in textual output of
 ghc in order to find errors quickly, not being tied to output ordering.

 == Disadvantages ==

 Many regression tests might need a fix.

--

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10021#comment:2>
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