Family consistency checks: add test for #26154

This commit adds the test T26154, to make sure that GHC doesn't crash
when performing type family consistency checks. This test case
was extracted from Agda.

Fixes #26154

Author: soulomoon

testsuite/tests/typecheck/should_compile/T26154.hs

@@ -0,0 +1,5 @@
+
+module T26154 where
+
+import {-# SOURCE #-} T26154_B
+import T26154_Other

testsuite/tests/typecheck/should_compile/T26154_A.hs

@@ -0,0 +1,9 @@
+
+{-# LANGUAGE TypeFamilies #-}
+
+module T26154_A where
+
+import {-# SOURCE #-} T26154_B
+
+type family F a b
+type instance F a b = b

testsuite/tests/typecheck/should_compile/T26154_B.hs

@@ -0,0 +1,9 @@
+{-# LANGUAGE TypeFamilies #-}
+
+module T26154_B where
+
+import T26154_A
+
+type family FAA a b
+
+type instance FAA a b = b

testsuite/tests/typecheck/should_compile/T26154_B.hs-boot

@@ -0,0 +1,3 @@
+{-# LANGUAGE TypeFamilies #-}
+
+module T26154_B where

testsuite/tests/typecheck/should_compile/T26154_Other.hs

@@ -0,0 +1,7 @@
+{-# LANGUAGE TypeFamilies #-}
+
+module T26154_Other where
+
+type family OtherF a b
+
+type instance OtherF a b = b

testsuite/tests/typecheck/should_compile/all.T

@@ -947,6 +947,7 @@ test('T25992', normal, compile, [''])
 test('T14010', normal, compile, [''])
 test('T26256a', normal, compile, [''])
 test('T25992a', normal, compile, [''])
+test('T26154', [extra_files(['T26154_A.hs', 'T26154_B.hs', 'T26154_B.hs-boot', 'T26154_Other.hs'])], multimod_compile, ['T26154', '-v0'])
 test('T26346', normal, compile, [''])
 test('T26358', expect_broken(26358), compile, [''])
 test('T26345', normal, compile, [''])