incomplete patterns and GADT

[nobody]

I would like to compile with 
-fwarn-incomplete-patterns and use GADTs, 
but I have bogus error messages. 
Suppose I define : 
 
data T a where 
    C1 :: T Char 
    C2 :: T Float 
 
then a function : 
 
exhaustive :: T Char -> Char 
exhaustive C1 = ' ' 
 
If I compile with incomplete pattern warnings, 
I get that my function "exhaustive" is not 
exhaustive. 
But if I add a case : 
 
exhaust C2 = ' ' 
 
then the compiler accurately warns me that this 
case is inaccessible. 
Would it be possible to add the accessibility check 
when compiling with incomplete patterns detection ? 

[igloo]

There's another case in 462.

[simonpj]

Dan Licata is planning to work on this.

Simon

[simonmar]

Could be done with #595.

[simonpj]

I have not done the full overhaul envisaged by #595, but it turned out to be rather easy to make GADTs play nicely with overlapping-pattern warnings.

   * Take account of GADTs when reporting patterm-match overlap
   Ignore-this: 7dcbdcb91021e83e6e6208a2e68c50c9
   When matching against a GADT, some of the constructors may be impossible.
    For example
   	data T a where
             T1 :: T Int
             T2 :: T Bool
             T3 :: T a
        f :: T Int ->  Int
        f T1 = 3
        f T3 = 4

   Here, does not have any missing cases, despite omittting T2, because
   T2 :: T Bool.

   This patch teaches the overlap checker about GADTs, which happily
   turned out to be rather easy even though the overlap checker needs
   a serious rewrite.

Simon