Add derived constraints for wildcard signatures

This fixes Trac #11016

See Note [Add deriveds for signature contexts] in TcSimplify]

3 files changed, 21 insertions, 0 deletions

diff --git a/testsuite/tests/partial-sigs/should_compile/T11016.hs b/testsuite/tests/partial-sigs/should_compile/T11016.hs
new file mode 100644
index 0000000000..02b7d4d3a8
--- /dev/null
+++ b/testsuite/tests/partial-sigs/should_compile/T11016.hs
@@ -0,0 +1,9 @@
+{-# LANGUAGE ImplicitParams, PartialTypeSignatures #-}
+
+module T11016 where
+
+f1 :: (?x :: Int, _) => Int
+f1 = ?x
+
+f2 :: (?x :: Int) => _
+f2 = ?x
diff --git a/testsuite/tests/partial-sigs/should_compile/T11016.stderr b/testsuite/tests/partial-sigs/should_compile/T11016.stderr
new file mode 100644
index 0000000000..74dd18d9bf
--- /dev/null
+++ b/testsuite/tests/partial-sigs/should_compile/T11016.stderr
@@ -0,0 +1,11 @@
+
+T11016.hs:5:19: warning:
+    Found constraint wildcard ‘_’ standing for ‘()’
+    In the type signature:
+      f1 :: (?x :: Int, _) => Int
+
+T11016.hs:8:22: warning:
+    • Found type wildcard ‘_’ standing for ‘Int’
+    • In the type signature:
+        f2 :: (?x :: Int) => _
+    • Relevant bindings include f2 :: Int (bound at T11016.hs:9:1)
diff --git a/testsuite/tests/partial-sigs/should_compile/all.T b/testsuite/tests/partial-sigs/should_compile/all.T
index 142d3318c8..5567ef1bdf 100644
--- a/testsuite/tests/partial-sigs/should_compile/all.T
+++ b/testsuite/tests/partial-sigs/should_compile/all.T
@@ -57,3 +57,4 @@ test('T10438', normal, compile, [''])
 test('T10519', normal, compile, [''])
 test('T10463', normal, compile, [''])
 test('ExprSigLocal', normal, compile, [''])
+test('T11016', normal, compile, [''])