[commit: ghc] master: Fix #13833: accept type literals with no FlexibleInstances (42f3b53)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/42f3b53b5bc4674e41f16de08094821fe1aaec00/ghc

>---------------------------------------------------------------

commit 42f3b53b5bc4674e41f16de08094821fe1aaec00
Author: Kirill Zaborsky <qrilka at gmail.com>
Date:   Fri Jun 15 14:12:58 2018 -0400

    Fix #13833: accept type literals with no FlexibleInstances
    
    Test Plan: ./validate
    
    Reviewers: bgamari, simonpj
    
    Reviewed By: bgamari, simonpj
    
    Subscribers: simonpj, rwbarton, thomie, carter
    
    GHC Trac Issues: #13833
    
    Differential Revision: https://phabricator.haskell.org/D4823


>---------------------------------------------------------------

42f3b53b5bc4674e41f16de08094821fe1aaec00
 compiler/typecheck/TcValidity.hs                   |  5 +++--
 docs/users_guide/8.6.1-notes.rst                   |  5 +++++
 testsuite/tests/typecheck/should_compile/T13833.hs | 12 ++++++++++++
 testsuite/tests/typecheck/should_compile/all.T     |  1 +
 4 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/compiler/typecheck/TcValidity.hs b/compiler/typecheck/TcValidity.hs
index 84309db..6d866f7 100644
--- a/compiler/typecheck/TcValidity.hs
+++ b/compiler/typecheck/TcValidity.hs
@@ -1121,12 +1121,13 @@ tcInstHeadTyNotSynonym ty
 
 tcInstHeadTyAppAllTyVars :: Type -> Bool
 -- Used in Haskell-98 mode, for the argument types of an instance head
--- These must be a constructor applied to type variable arguments.
+-- These must be a constructor applied to type variable arguments
+-- or a type-level literal.
 -- But we allow kind instantiations.
 tcInstHeadTyAppAllTyVars ty
   | Just (tc, tys) <- tcSplitTyConApp_maybe (dropCasts ty)
   = ok (filterOutInvisibleTypes tc tys)  -- avoid kinds
-
+  | LitTy _ <- ty = True  -- accept type literals (Trac #13833)
   | otherwise
   = False
   where
diff --git a/docs/users_guide/8.6.1-notes.rst b/docs/users_guide/8.6.1-notes.rst
index 147558e..4bc01c9 100644
--- a/docs/users_guide/8.6.1-notes.rst
+++ b/docs/users_guide/8.6.1-notes.rst
@@ -125,6 +125,11 @@ Language
 
   This is now an error unless :extension:`PolyKinds` is enabled.
 
+- Type literals now could be used in type class instances without the extension
+  :extension:`FlexibleInstances`.
+
+  See :ghc-ticket:`13833`.
+
 Compiler
 ~~~~~~~~
 
diff --git a/testsuite/tests/typecheck/should_compile/T13833.hs b/testsuite/tests/typecheck/should_compile/T13833.hs
new file mode 100644
index 0000000..266b00b
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T13833.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE DataKinds, KindSignatures #-}
+
+import GHC.TypeLits (Nat, Symbol)
+
+class A (n::Nat)
+instance A 0
+
+class B (s::Symbol)
+instance B "B"
+
+main :: IO ()
+main = return ()
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index 8a7a7da..beaea5d 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -623,3 +623,4 @@ test('T15050', [expect_broken(15050)], compile, [''])
 test('T14735', normal, compile, [''])
 test('T15180', normal, compile, [''])
 test('T15232', normal, compile, [''])
+test('T13833', normal, compile, [''])
\ No newline at end of file