Add test cases for explicitly-bidirectional pattern synonym

testsuite/.gitignore

@@ -1068,6 +1068,8 @@ mk/ghcconfig_*_inplace_bin_ghc-stage2.exe.mk
 /tests/parser/unicode/1744
 /tests/parser/unicode/T1744
 /tests/parser/unicode/utf8_024
+/tests/patsyn/should_run/bidir-explicit
+/tests/patsyn/should_run/bidir-explicit-scope
 /tests/patsyn/should_run/eval
 /tests/patsyn/should_run/ex-prov
 /tests/patsyn/should_run/ex-prov-run

testsuite/tests/patsyn/should_run/all.T

 test('eval', normal, compile_and_run, [''])
 test('match', normal, compile_and_run, [''])
 test('ex-prov-run', normal, compile_and_run, [''])
+test('bidir-explicit', normal, compile_and_run, [''])
+test('bidir-explicit-scope', normal, compile_and_run, [''])

testsuite/tests/patsyn/should_run/bidir-explicit-scope.hs

+{-# LANGUAGE PatternSynonyms #-}
+module Main where
+
+pattern First x <- x:_ where
+  First x = foo [x, x, x]
+
+foo :: [a] -> [a]
+foo xs@(First x) = replicate (length xs + 1) x
+
+main = mapM_ print $ First ()

testsuite/tests/patsyn/should_run/bidir-explicit-scope.stdout

+()
+()
+()
+()

testsuite/tests/patsyn/should_run/bidir-explicit.hs

+{-# LANGUAGE PatternSynonyms #-}
+module Main where
+
+pattern First x <- x:_ where
+  First x = [x]
+
+main = mapM_ print $ First ()

testsuite/tests/patsyn/should_run/bidir-explicit.stdout

+()