Add a Template Haskell warning flag -Wimplicit-lift

Part of #17804.

3 files changed, 37 insertions, 0 deletions

diff --git a/testsuite/tests/th/T17804.hs b/testsuite/tests/th/T17804.hs
new file mode 100644
index 0000000000..152812a728
--- /dev/null
+++ b/testsuite/tests/th/T17804.hs
@@ -0,0 +1,26 @@
+{-# OPTIONS_GHC -Wimplicit-lift #-}
+{-# LANGUAGE TemplateHaskell #-}
+module T17804 where
+
+import Language.Haskell.TH.Syntax
+
+warning1 :: Lift t => t -> Q Exp
+warning1 x = [| x |]
+
+warning2 :: Lift t => t -> Code Q t
+warning2 x = [|| x ||]
+
+noWarning1 :: Q Exp
+noWarning1 = [| \x -> x |]
+
+noWarning2 :: Code Q (a -> a)
+noWarning2 = [|| \x -> x ||]
+
+i :: Int
+i = 0
+
+noWarning3 :: Q Exp
+noWarning3 = [| i |]
+
+noWarning4 :: Code Q Int
+noWarning4 = [|| i ||]
diff --git a/testsuite/tests/th/T17804.stderr b/testsuite/tests/th/T17804.stderr
new file mode 100644
index 0000000000..6a18945635
--- /dev/null
+++ b/testsuite/tests/th/T17804.stderr
@@ -0,0 +1,10 @@
+
+T17804.hs:8:17: warning: [-Wimplicit-lift]
+    • The variable ‘x’ is implicitly lifted in the TH quotation
+    • In the Template Haskell quotation [| x |]
+
+T17804.hs:11:18: warning: [-Wimplicit-lift]
+    • The variable ‘x’ is implicitly lifted in the TH quotation
+    • In the Template Haskell quotation [|| x ||]
+      In the expression: [|| x ||]
+      In an equation for ‘warning2’: warning2 x = [|| x ||]
diff --git a/testsuite/tests/th/all.T b/testsuite/tests/th/all.T
index 235c0148f7..fbc8428503 100644
--- a/testsuite/tests/th/all.T
+++ b/testsuite/tests/th/all.T
@@ -520,3 +520,4 @@ test('T18740c', normal, compile_fail, [''])
 test('T18740d', normal, compile_fail, [''])
 test('T19363', normal, compile_and_run, [''])
 test('T19377', normal, compile, [''])
+test('T17804', normal, compile, [''])