From 6738c01d6175c5701e5c53e2ae6716d1103f7355 Mon Sep 17 00:00:00 2001
From: Krzysztof Gogolewski <krzysztof.gogolewski@tweag.io>
Date: Mon, 17 Apr 2023 10:31:32 +0200
Subject: Add a regression test for #21050

---
 testsuite/tests/th/T21050.hs     | 11 +++++++++++
 testsuite/tests/th/T21050.stderr | 26 ++++++++++++++++++++++++++
 testsuite/tests/th/all.T         |  1 +
 3 files changed, 38 insertions(+)
 create mode 100644 testsuite/tests/th/T21050.hs
 create mode 100644 testsuite/tests/th/T21050.stderr

diff --git a/testsuite/tests/th/T21050.hs b/testsuite/tests/th/T21050.hs
new file mode 100644
index 0000000000..6c31b7a3f4
--- /dev/null
+++ b/testsuite/tests/th/T21050.hs
@@ -0,0 +1,11 @@
+{-# LANGUAGE TemplateHaskell, ImpredicativeTypes #-}
+module T21050 where
+
+import Language.Haskell.TH.Syntax
+
+data T = MkT (forall a. a)
+
+f x = [|| MkT $$(x) ||]
+
+g :: Code Q (forall a. a) -> Code Q T
+g x = [|| MkT $$(x) ||]
diff --git a/testsuite/tests/th/T21050.stderr b/testsuite/tests/th/T21050.stderr
new file mode 100644
index 0000000000..4d2a84e274
--- /dev/null
+++ b/testsuite/tests/th/T21050.stderr
@@ -0,0 +1,26 @@
+
+T21050.hs:8:18: error: [GHC-25897]
+    • Couldn't match expected type ‘Code m a1’ with actual type ‘p’
+      ‘p’ is a rigid type variable bound by
+        the inferred type of f :: Quote m => p -> Code m T
+        at T21050.hs:8:1-23
+    • In the expression: x
+      In the Template Haskell splice $$(x)
+      In the first argument of ‘MkT’, namely ‘$$(x)’
+    • Relevant bindings include
+        x :: p (bound at T21050.hs:8:3)
+        f :: p -> Code m T (bound at T21050.hs:8:1)
+
+T21050.hs:11:18: error: [GHC-91028]
+    • Couldn't match type ‘a’ with ‘forall a2. a2’
+      Expected: Code Q a
+        Actual: Code Q (forall a. a)
+      Cannot equate type variable ‘a’
+      with a type involving polytypes: forall a2. a2
+      ‘a’ is a rigid type variable bound by
+        a type expected by the context:
+          forall a. a
+        at T21050.hs:11:15-19
+    • In the expression: x
+      In the Template Haskell splice $$(x)
+      In the first argument of ‘MkT’, namely ‘$$(x)’
diff --git a/testsuite/tests/th/all.T b/testsuite/tests/th/all.T
index 60f02a9c2e..3a98df38ee 100644
--- a/testsuite/tests/th/all.T
+++ b/testsuite/tests/th/all.T
@@ -564,3 +564,4 @@ test('TH_typed2', normal, compile_and_run, [''])
 test('TH_typed3', normal, compile, ['-v0 -ddump-splices -dsuppress-uniques'])
 test('TH_typed4', normal, compile, ['-v0 -ddump-splices -dsuppress-uniques'])
 test('TH_typed5', normal, compile_and_run, [''])
+test('T21050', normal, compile_fail, [''])
-- 
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