Add test for #16038

testsuite/tests/simplCore/should_compile/T16038/A.hs

+module A where
+
+import B
+
+data HsExpr id
+  = HsOverLit (HsOverLit id)
+  | HsBracketOut (HsExpr id)
+  deriving Eq
+

testsuite/tests/simplCore/should_compile/T16038/A.hs-boot

+module A where
+
+data HsExpr i
+
+instance Eq i => Eq (HsExpr i)
+

testsuite/tests/simplCore/should_compile/T16038/B.hs

+module B where
+
+import {-# SOURCE #-} A (HsExpr)
+
+data HsOverLit id
+  = OverLit (HsExpr id)
+  deriving Eq

testsuite/tests/simplCore/should_compile/T16038/Makefile

+TOP=../../../..
+include $(TOP)/mk/boilerplate.mk
+include $(TOP)/mk/test.mk
+
+T16038:
+	'$(TEST_HC)' $(TEST_HC_OPTS) -O -c A.hs-boot
+	'$(TEST_HC)' $(TEST_HC_OPTS) -O -c B.hs
+	# All `fEqHsExpr` bindings should be in one recursive group:
+	'$(TEST_HC)' $(TEST_HC_OPTS) -O -c A.hs -ddump-simpl -dsuppress-all | \
+		grep -e "^\$$fEqHsExpr" -e "Rec"

testsuite/tests/simplCore/should_compile/T16038/T16038.stdout

+Rec {
+$fEqHsExpr_$c/=
+$fEqHsExpr_$c/=
+$fEqHsExpr
+$fEqHsExpr
+$fEqHsExpr_$c==
+$fEqHsExpr_$c==
+end Rec }

testsuite/tests/simplCore/should_compile/T16038/test.T

+test('T16038',
+     [extra_files(['A.hs', 'A.hs-boot', 'B.hs'])],
+     run_command,
+     ['$MAKE -s --no-print-directory T16038'])