From 478138c03fa30c17e37d26a0a9ad76d357a6a645 Mon Sep 17 00:00:00 2001
From: Krzysztof Gogolewski <krzysztof.gogolewski@tweag.io>
Date: Mon, 8 May 2023 18:48:33 +0200
Subject: Add a test for #17284

Since !10123 we now reject this program.
---
 compiler/GHC/Tc/Types.hs                            | 2 +-
 testsuite/tests/typecheck/should_fail/T17284.hs     | 9 +++++++++
 testsuite/tests/typecheck/should_fail/T17284.stderr | 4 ++++
 testsuite/tests/typecheck/should_fail/all.T         | 1 +
 4 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 testsuite/tests/typecheck/should_fail/T17284.hs
 create mode 100644 testsuite/tests/typecheck/should_fail/T17284.stderr

diff --git a/compiler/GHC/Tc/Types.hs b/compiler/GHC/Tc/Types.hs
index a6bab74fc0..28668b7979 100644
--- a/compiler/GHC/Tc/Types.hs
+++ b/compiler/GHC/Tc/Types.hs
@@ -1592,7 +1592,7 @@ instance Outputable TcIdSigInfo where
     ppr (CompleteSig { sig_bndr = bndr })
         = ppr bndr <+> dcolon <+> ppr (idType bndr)
     ppr (PartialSig { psig_name = name, psig_hs_ty = hs_ty })
-        = text "psig" <+> ppr name <+> dcolon <+> ppr hs_ty
+        = text "[partial signature]" <+> ppr name <+> dcolon <+> ppr hs_ty
 
 instance Outputable TcIdSigInst where
     ppr (TISI { sig_inst_sig = sig, sig_inst_skols = skols
diff --git a/testsuite/tests/typecheck/should_fail/T17284.hs b/testsuite/tests/typecheck/should_fail/T17284.hs
new file mode 100644
index 0000000000..d32dce2ba0
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T17284.hs
@@ -0,0 +1,9 @@
+{-# LANGUAGE MonomorphismRestriction #-}
+{-# LANGUAGE PartialTypeSignatures #-}
+
+module MonoPoly where
+
+f :: Num a => a -> _
+f x = x + y
+
+y = f 1
diff --git a/testsuite/tests/typecheck/should_fail/T17284.stderr b/testsuite/tests/typecheck/should_fail/T17284.stderr
new file mode 100644
index 0000000000..992f147089
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T17284.stderr
@@ -0,0 +1,4 @@
+
+T17284.hs:6:1: error: [GHC-16675]
+    Overloaded signature conflicts with monomorphism restriction
+      [partial signature] f :: Num a => a -> _
diff --git a/testsuite/tests/typecheck/should_fail/all.T b/testsuite/tests/typecheck/should_fail/all.T
index f13dd45b08..f62ee5e355 100644
--- a/testsuite/tests/typecheck/should_fail/all.T
+++ b/testsuite/tests/typecheck/should_fail/all.T
@@ -681,3 +681,4 @@ test('LazyFieldsDisabled', normal, compile_fail, [''])
 test('TyfamsDisabled', normal, compile_fail, [''])
 test('CommonFieldResultTypeMismatch', normal, compile_fail, [''])
 test('CommonFieldTypeMismatch', normal, compile_fail, [''])
+test('T17284', normal, compile_fail, [''])
-- 
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