Implement -Wforall-identifier (#20609)

In accordance with GHC Proposal #281 "Visible forall in types of terms":

	For three releases before this change takes place, include a new
	warning -Wforall-identifier in -Wdefault. This warning will be triggered
	at definition sites (but not use sites) of forall as an identifier.

Updates the haddock submodule.

15 files changed, 163 insertions, 5 deletions

diff --git a/testsuite/tests/ghci/prog017/TopLevel.hs b/testsuite/tests/ghci/prog017/TopLevel.hs
index c2e562b1f9..6e9d38812a 100644
--- a/testsuite/tests/ghci/prog017/TopLevel.hs
+++ b/testsuite/tests/ghci/prog017/TopLevel.hs
@@ -72,8 +72,8 @@ import Level2.Level2
 (➾➔) = undefined :: () -- ... U+2794
 
 -- mathematicalOperators
-(∀) = undefined :: () -- U+2200
-(∀⋙) = undefined :: () -- ... U+22D9
+(∁) = undefined :: () -- U+2201 (skip U+2200 because it's the keyword ∀)
+(∁⋙) = undefined :: () -- ... U+22D9
 
 -- miscellaneousMathematicalSymbolsAR
 (⟑) = undefined :: () -- U+27D1
diff --git a/testsuite/tests/ghci/prog017/prog017.script b/testsuite/tests/ghci/prog017/prog017.script
index 302233869b..7144d087fd 100644
--- a/testsuite/tests/ghci/prog017/prog017.script
+++ b/testsuite/tests/ghci/prog017/prog017.script
@@ -61,7 +61,7 @@
 :complete repl "➾"
 
 -- mathematicalOperators
-:complete repl "∀"
+:complete repl "∁"
 
 -- miscellaneousMathematicalSymbolsAR
 :complete repl "⟑"
diff --git a/testsuite/tests/ghci/prog017/prog017.stdout b/testsuite/tests/ghci/prog017/prog017.stdout
index 903660d369..57b1ba0d6c 100644
--- a/testsuite/tests/ghci/prog017/prog017.stdout
+++ b/testsuite/tests/ghci/prog017/prog017.stdout
@@ -68,8 +68,8 @@
 "\10174"
 "\10174\10132"
 2 2 ""
-"\8704"
-"\8704\8921"
+"\8705"
+"\8705\8921"
 2 2 ""
 "\10193"
 "\10193\10193"
diff --git a/testsuite/tests/rename/should_compile/ExplicitForAllRules1.stderr b/testsuite/tests/rename/should_compile/ExplicitForAllRules1.stderr
index 5852074450..88c7e7c771 100644
--- a/testsuite/tests/rename/should_compile/ExplicitForAllRules1.stderr
+++ b/testsuite/tests/rename/should_compile/ExplicitForAllRules1.stderr
@@ -1,4 +1,11 @@
 
+ExplicitForAllRules1.hs:46:31: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+
 ExplicitForAllRules1.hs:49:31: warning: [-Wunused-foralls (in -Wextra)]
     Unused quantified type variable ‘b’
     In the rewrite rule "example7"
diff --git a/testsuite/tests/rename/should_compile/T20609.hs b/testsuite/tests/rename/should_compile/T20609.hs
new file mode 100644
index 0000000000..7e8955f29f
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609.hs
@@ -0,0 +1,23 @@
+module T20609 where
+
+-- Triggers the warning (definition/binding sites):
+-- ------------------------------------------------
+
+forall x = ()
+
+(∀) x = ()
+
+fparam forall = ()
+
+asPattern forall@Nothing = ()
+
+localLet = let forall = () in forall
+
+{-# RULES "rule" forall forall. id forall = forall #-}
+
+{-# RULES "rule_sig" forall a. forall (forall :: a). id forall = forall #-}
+
+-- Does not trigger the warning (use sites):
+-- -----------------------------------------
+
+other = forall
diff --git a/testsuite/tests/rename/should_compile/T20609.stderr b/testsuite/tests/rename/should_compile/T20609.stderr
new file mode 100644
index 0000000000..a9958e2b85
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609.stderr
@@ -0,0 +1,49 @@
+
+T20609.hs:6:1: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+
+T20609.hs:8:1: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘∀’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+
+T20609.hs:10:8: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+
+T20609.hs:12:11: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+
+T20609.hs:14:16: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+
+T20609.hs:16:25: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+
+T20609.hs:18:40: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
diff --git a/testsuite/tests/rename/should_compile/T20609a.hs b/testsuite/tests/rename/should_compile/T20609a.hs
new file mode 100644
index 0000000000..0cf753760f
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609a.hs
@@ -0,0 +1,12 @@
+module T20609a where
+
+-- Triggers the warning (definition/binding sites):
+-- ------------------------------------------------
+
+data MyRecord a = R { forall :: a }
+
+-- Does not trigger the warning (use sites):
+-- -----------------------------------------
+
+x = forall (R { forall = () })
+f (R { forall = r }) = r
diff --git a/testsuite/tests/rename/should_compile/T20609a.stderr b/testsuite/tests/rename/should_compile/T20609a.stderr
new file mode 100644
index 0000000000..d828a1b269
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609a.stderr
@@ -0,0 +1,7 @@
+
+T20609a.hs:6:23: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
diff --git a/testsuite/tests/rename/should_compile/T20609b.hs b/testsuite/tests/rename/should_compile/T20609b.hs
new file mode 100644
index 0000000000..2e08bdcee2
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609b.hs
@@ -0,0 +1,13 @@
+module T20609b where
+
+-- Triggers the warning (definition/binding sites):
+-- ------------------------------------------------
+
+class MyClass c where
+  forall :: c -> ()
+
+-- Does not trigger the warning (use sites):
+-- -----------------------------------------
+
+instance MyClass () where
+  forall = id
diff --git a/testsuite/tests/rename/should_compile/T20609b.stderr b/testsuite/tests/rename/should_compile/T20609b.stderr
new file mode 100644
index 0000000000..c356dde8b0
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609b.stderr
@@ -0,0 +1,7 @@
+
+T20609b.hs:7:3: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
diff --git a/testsuite/tests/rename/should_compile/T20609c.hs b/testsuite/tests/rename/should_compile/T20609c.hs
new file mode 100644
index 0000000000..2e36f8c7e1
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609c.hs
@@ -0,0 +1,8 @@
+{-# LANGUAGE PatternSynonyms #-}
+
+module T20609c where
+
+pattern Pat forall = forall
+
+pattern RPat { forall } = forall
+
diff --git a/testsuite/tests/rename/should_compile/T20609c.stderr b/testsuite/tests/rename/should_compile/T20609c.stderr
new file mode 100644
index 0000000000..c22ead3d0b
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609c.stderr
@@ -0,0 +1,14 @@
+
+T20609c.hs:5:22: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+
+T20609c.hs:7:27: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
diff --git a/testsuite/tests/rename/should_compile/T20609d.hs b/testsuite/tests/rename/should_compile/T20609d.hs
new file mode 100644
index 0000000000..bed945bcfa
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609d.hs
@@ -0,0 +1,6 @@
+module T20609d where
+
+import Data.Word (Word8)
+
+foreign import ccall unsafe "forall"
+  forall :: IO Word8
diff --git a/testsuite/tests/rename/should_compile/T20609d.stderr b/testsuite/tests/rename/should_compile/T20609d.stderr
new file mode 100644
index 0000000000..8060b3298f
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T20609d.stderr
@@ -0,0 +1,7 @@
+
+T20609d.hs:6:3: warning: [-Wforall-identifier (in -Wdefault)]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
diff --git a/testsuite/tests/rename/should_compile/all.T b/testsuite/tests/rename/should_compile/all.T
index 2148470c66..8e55b3705a 100644
--- a/testsuite/tests/rename/should_compile/all.T
+++ b/testsuite/tests/rename/should_compile/all.T
@@ -177,3 +177,8 @@ test('T18302', expect_broken(18302), compile, [''])
 test('T17853', [], multimod_compile, ['T17853', '-v0'])
 test('T19966', expect_broken(19966), compile, ['-fdefer-out-of-scope-variables'])
 test('T20472', normal, compile, [''])
+test('T20609', normal, compile, [''])
+test('T20609a', normal, compile, [''])
+test('T20609b', normal, compile, [''])
+test('T20609c', normal, compile, [''])
+test('T20609d', normal, compile, [''])