Location for tuple section pattern error (#19504)

This fixes a regression that led to loss of location information
in error messages about the use of tuple sections in patterns.

compiler/GHC/Parser/PostProcess.hs

@@ -2670,7 +2670,9 @@ mkSumOrTuplePat l boxity (Tuple ps) = do
   return $ L l (PatBuilderPat (TuplePat noExtField ps' boxity))
   where
     toTupPat :: Located (Maybe (Located (PatBuilder GhcPs))) -> PV (LPat GhcPs)
-    toTupPat (L l p) = case p of
+    -- Ignore the element location so that the error message refers to the
+    -- entire tuple. See #19504 (and the discussion) for details.
+    toTupPat (L _ p) = case p of
       Nothing -> addFatalError $ PsError PsErrTupleSectionInPat [] l
       Just p' -> checkLPat p'
 

testsuite/tests/parser/should_fail/T19504.hs

+module T19504 where
+
+error_notLocated = (\ (0,  ) -> (0, undefined))

testsuite/tests/parser/should_fail/T19504.stderr

+
+T19504.hs:3:23: error: Tuple section in pattern context

testsuite/tests/parser/should_fail/all.T

@@ -189,3 +189,4 @@ test('RecordDotSyntaxFail10', normal, compile_fail, [''])
 test('RecordDotSyntaxFail11', normal, compile_fail, [''])
 test('RecordDotSyntaxFail12', normal, compile_fail, [''])
 test('RecordDotSyntaxFail13', normal, compile_fail, [''])
+test('T19504', normal, compile_fail, [''])