From ee1161d3f2a76ee91c415164ede4edfea3c301a9 Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Wed, 23 Dec 2020 16:47:16 +0000
Subject: Add regression test for #18467

---
 testsuite/tests/typecheck/should_compile/T18467.hs     | 12 ++++++++++++
 testsuite/tests/typecheck/should_compile/T18467.stderr | 17 +++++++++++++++++
 testsuite/tests/typecheck/should_compile/all.T         |  2 ++
 3 files changed, 31 insertions(+)
 create mode 100644 testsuite/tests/typecheck/should_compile/T18467.hs
 create mode 100644 testsuite/tests/typecheck/should_compile/T18467.stderr

diff --git a/testsuite/tests/typecheck/should_compile/T18467.hs b/testsuite/tests/typecheck/should_compile/T18467.hs
new file mode 100644
index 0000000000..b105edf3d8
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T18467.hs
@@ -0,0 +1,12 @@
+{-# OPTIONS_GHC -fdefer-type-errors #-}
+
+module T18467 where
+
+----------------------
+x = 3   -- Monomorphism restriction; we get x::alpha
+
+f y = x::Float
+g z = x::Int
+
+-------------
+h v = let t = \y -> (v, y : y) in fst (t True)
diff --git a/testsuite/tests/typecheck/should_compile/T18467.stderr b/testsuite/tests/typecheck/should_compile/T18467.stderr
new file mode 100644
index 0000000000..7ebf51de6f
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T18467.stderr
@@ -0,0 +1,17 @@
+
+T18467.hs:9:7: warning: [-Wdeferred-type-errors (in -Wdefault)]
+    • Couldn't match expected type ‘Int’ with actual type ‘Float’
+    • In the expression: x :: Int
+      In an equation for ‘g’: g z = x :: Int
+
+T18467.hs:12:29: warning: [-Wdeferred-type-errors (in -Wdefault)]
+    • Couldn't match expected type ‘[a1]’ with actual type ‘a1’
+      ‘a1’ is a rigid type variable bound by
+        the inferred type of t :: a1 -> (a, [a1])
+        at T18467.hs:12:11-30
+    • In the second argument of ‘(:)’, namely ‘y’
+      In the expression: y : y
+      In the expression: (v, y : y)
+    • Relevant bindings include
+        y :: a1 (bound at T18467.hs:12:16)
+        t :: a1 -> (a, [a1]) (bound at T18467.hs:12:11)
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index da663d484b..a461ed7257 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -764,3 +764,5 @@ test('InlinePatSyn_NoInlineBuilder', [], makefile_test, [])
 test('InlinePatSyn_NoInlineMatcher', [], makefile_test, [])
 test('InlinePatSyn_ExplicitBidiBuilder', [], makefile_test, [])
 test('InlinePatSyn_ExplicitBidiMatcher', [], makefile_test, [])
+test('T18467', normal, compile, [''])
+
-- 
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