PmCheck: Disattach COMPLETE pragma lookup from TyCons

By not attaching COMPLETE pragmas with a particular TyCon and instead
assume that every COMPLETE pragma is applicable everywhere, we can
drastically simplify the logic that tries to initialise available
COMPLETE sets of a variable during the pattern-match checking process,
as well as fixing a few bugs.

Of course, we have to make sure not to report any of the
ill-typed/unrelated COMPLETE sets, which came up in a few regression
tests.

In doing so, we fix #17207, #18277 and #14422.

There was a metric decrease in #18478 by ~20%.

Metric Decrease:
    T18478

7 files changed, 39 insertions, 13 deletions

diff --git a/testsuite/tests/pmcheck/complete_sigs/completesig15.hs b/testsuite/tests/pmcheck/complete_sigs/T14422.hs
index 5936379aa7..be879f4b13 100644
--- a/testsuite/tests/pmcheck/complete_sigs/completesig15.hs
+++ b/testsuite/tests/pmcheck/complete_sigs/T14422.hs
@@ -10,3 +10,6 @@ pattern P :: C f => f a
 pattern P <- (foo -> ())
 
 {-# COMPLETE P #-}
+
+f :: C f => f a -> ()
+f P = () -- A complete match
diff --git a/testsuite/tests/pmcheck/complete_sigs/T18277.hs b/testsuite/tests/pmcheck/complete_sigs/T18277.hs
new file mode 100644
index 0000000000..db09edf65a
--- /dev/null
+++ b/testsuite/tests/pmcheck/complete_sigs/T18277.hs
@@ -0,0 +1,13 @@
+{-# OPTIONS_GHC -Wincomplete-patterns -fforce-recomp #-}
+{-# LANGUAGE PatternSynonyms #-}
+
+module Lib where
+
+type List = []
+
+pattern DefinitelyAString :: String -> String
+pattern DefinitelyAString x = x
+{-# COMPLETE DefinitelyAString #-}
+
+f :: String -> String
+f (DefinitelyAString x) = x
diff --git a/testsuite/tests/pmcheck/complete_sigs/all.T b/testsuite/tests/pmcheck/complete_sigs/all.T
index bc4f39ac39..2728121160 100644
--- a/testsuite/tests/pmcheck/complete_sigs/all.T
+++ b/testsuite/tests/pmcheck/complete_sigs/all.T
@@ -1,7 +1,7 @@
 test('completesig01', normal, compile, [''])
 test('completesig02', normal, compile, [''])
 test('Completesig03', normal, multimod_compile, ['Completesig03', '-Wall'])
-test('completesig04', normal, compile_fail, [''])
+test('completesig04', normal, compile, ['-Wincomplete-patterns'])
 test('completesig05', normal, compile, [''])
 test('completesig06', normal, compile, [''])
 test('completesig07', normal, compile, [''])
@@ -12,7 +12,6 @@ test('completesig11', normal, compile, [''])
 test('completesig12', normal, compile, [''])
 test('completesig13', normal, compile, [''])
 test('completesig14', normal, compile, [''])
-test('completesig15', normal, compile_fail, [''])
 test('T13021', normal, compile, [''])
 test('T13363a', normal, compile, [''])
 test('T13363b', normal, compile, [''])
@@ -22,6 +21,8 @@ test('T13965', normal, compile, [''])
 test('T14059a', normal, compile, [''])
 test('T14059b', expect_broken('14059'), compile, [''])
 test('T14253', normal, compile, [''])
+test('T14422', normal, compile, [''])
 test('T14851', normal, compile, [''])
 test('T17149', normal, compile, [''])
 test('T17386', normal, compile, [''])
+test('T18277', normal, compile, [''])
diff --git a/testsuite/tests/pmcheck/complete_sigs/completesig04.hs b/testsuite/tests/pmcheck/complete_sigs/completesig04.hs
index dbe1110be1..d8f84cb71d 100644
--- a/testsuite/tests/pmcheck/complete_sigs/completesig04.hs
+++ b/testsuite/tests/pmcheck/complete_sigs/completesig04.hs
@@ -1,6 +1,12 @@
--- Test that a COMPLETE pragma over constructors of different types fails.
+{-# OPTIONS_GHC -Wincomplete-patterns -fforce-recomp #-}
+-- Test that a COMPLETE pragma over constructors of different types is a valid
+-- declaration, but that it's not suggested in any warning.
 module TyMismatch where
 
-data E = L | R
+data T = A | B | C
 
-{-# COMPLETE Just, L #-}
+{-# COMPLETE Just, A #-}
+
+f A = ()        -- should not suggest 'Just'
+
+g (Just _) = () -- should not suggest 'A'
diff --git a/testsuite/tests/pmcheck/complete_sigs/completesig04.stderr b/testsuite/tests/pmcheck/complete_sigs/completesig04.stderr
index 21a6377ba3..a114d0199e 100644
--- a/testsuite/tests/pmcheck/complete_sigs/completesig04.stderr
+++ b/testsuite/tests/pmcheck/complete_sigs/completesig04.stderr
@@ -1,4 +1,11 @@
 
-completesig04.hs:6:1: error:
-    • Cannot form a group of complete patterns from patterns ‘Just’ and ‘L’ as they match different type constructors (‘Maybe’ resp. ‘E’)
-    • In {-# COMPLETE Just, L #-}
+completesig04.hs:10:1: warning: [-Wincomplete-patterns (in -Wextra)]
+    Pattern match(es) are non-exhaustive
+    In an equation for ‘f’:
+        Patterns not matched:
+            B
+            C
+
+completesig04.hs:12:1: warning: [-Wincomplete-patterns (in -Wextra)]
+    Pattern match(es) are non-exhaustive
+    In an equation for ‘g’: Patterns not matched: Nothing
diff --git a/testsuite/tests/pmcheck/complete_sigs/completesig15.stderr b/testsuite/tests/pmcheck/complete_sigs/completesig15.stderr
deleted file mode 100644
index 3bff495ebe..0000000000
--- a/testsuite/tests/pmcheck/complete_sigs/completesig15.stderr
+++ /dev/null
@@ -1,4 +0,0 @@
-
-completesig15.hs:12:1: error:
-    • A type signature must be provided for a set of polymorphic pattern synonyms.
-    • In {-# COMPLETE P #-}
diff --git a/testsuite/tests/pmcheck/should_compile/all.T b/testsuite/tests/pmcheck/should_compile/all.T
index de0998ba29..e8938be163 100644
--- a/testsuite/tests/pmcheck/should_compile/all.T
+++ b/testsuite/tests/pmcheck/should_compile/all.T
@@ -88,7 +88,7 @@ test('T17112', normal, compile,
      ['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
 test('T17207', normal, compile,
      ['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
-test('T17207b', expect_broken(17207), compile,
+test('T17207b', normal, compile,
      ['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])
 test('T17208', expect_broken(17208), compile,
      ['-fwarn-incomplete-patterns -fwarn-overlapping-patterns'])