Use line pragmas for better error locations

[Toxaris]

The Haskell pretty printer should generate {-# LINE ... #-} pragmas so that GHC error messages can point to locations in the source files (instead of locations in the generated files).

Example:

I have a file src/Foo/Bar/Test.shs:

module Foo.Bar.Test where

// main :: IO ()
main = "foo" + 13

SugarJ generates the following in bin/Foo/Bar/Test.hs:

module Foo.Bar.Test where
main = ( "foo" + 13 )  where {  }

This program does not typecheck, because the use of + in line 3 of Test.shs is not correct. GHC reports the problem, but points to line 2 of Test.hs:

    C:\eclipse\sugarj\workspace\test-project\bin\Foo\Bar\Test.hs:2:16:
        No instance for (Num [Char])
          arising from a use of `+'
        Possible fix: add an instance declaration for (Num [Char])
        In the expression: ("foo" + 13)
        In an equation for `main': main = ("foo" + 13)

It would be better if SugarJ could generate the following bin/Foo/Bar/Test.hs instead:

{-# LINE 1 "C:/eclipse/sugarj/workspace/test-project/src/Foo/Bar/Test.shs" #-}
module Foo.Bar.Test where
{-# LINE 3 "C:/eclipse/sugarj/workspace/test-project/src/Foo/Bar/Test.shs" #-}
main = ( "foo" + 13 )  where {  }

GHC would use the information in the LINE-pragmas to generate the following error message, which points to the correct line in the correct file:

C:\eclipse\sugarj\workspace\test-project\src\Foo\Bar\Test.shs:3:16:
    No instance for (Num [Char])
      arising from a use of `+'
    Possible fix: add an instance declaration for (Num [Char])
    In the expression: ("foo" + 13)
    In an equation for `main': main = ("foo" + 13)

Even better would be if SugarJ would parse this error messages and display it as an error marker on the line.