add partial support for parens at the query expression level

Language/SQL/SimpleSQL/Parse.hs

@@ -651,7 +651,11 @@ scalar expression parens, row ctor and scalar subquery
 
 parensExpr :: Parser ScalarExpr
 parensExpr = parens $ choice
-    [SubQueryExpr SqSq <$> queryExpr
+    -- no parens here used for nested parens expressions
+    -- this could be fixed to be general with some refactoring, but at
+    -- the moment, you can't use additional redundant parens in a
+    -- subqueryexpr
+    [SubQueryExpr SqSq <$> queryExprNoParens
     ,ctor <$> commaSep1 scalarExpr]
   where
     ctor [a] = Parens a
@@ -1443,7 +1447,9 @@ from = label "from" (keyword_ "from" *> commaSep1 tref)
     nonJoinTref =
         label "table ref" $ choice
         [hidden $ parens $ choice
-             [TRQueryExpr <$> queryExpr
+             -- will be tricky to figure out how to support mixes of nested
+             -- query expr parens and table ref parens
+             [TRQueryExpr <$> queryExprNoParens
              ,TRParens <$> tref]
         ,TRLateral <$> (hidden (keyword_ "lateral") *> nonJoinTref)
         ,do
@@ -1586,9 +1592,18 @@ and union, etc..
 -}
 
 queryExpr :: Parser QueryExpr
-queryExpr = label "query expr" $ E.makeExprParser qeterm qeOpTable
+queryExpr = queryExpr' True
+queryExprNoParens :: Parser QueryExpr
+queryExprNoParens = queryExpr' False
+
+queryExpr' :: Bool -> Parser QueryExpr
+queryExpr' allowParens = label "query expr" $ E.makeExprParser qeterm qeOpTable
   where
-    qeterm = label "query expr" (with <|> select <|> table <|> values)
+    qeterm
+        | allowParens =
+              label "query expr" (with <|> select <|> table <|> values <|> qeParens)
+        | otherwise =
+              label "query expr" (with <|> select <|> table <|> values)
 
     select = keyword_ "select" >>
         mkSelect
@@ -1602,6 +1617,7 @@ queryExpr = label "query expr" $ E.makeExprParser qeterm qeOpTable
     values = keyword_ "values"
              >> Values <$> commaSep (parens (commaSep scalarExpr))
     table = keyword_ "table" >> Table <$> names "table name"
+    qeParens = QueryExprParens <$> parens queryExpr
 
     qeOpTable =
         [[E.InfixL $ setOp Intersect "intersect"]

simple-sql-parser.cabal

@@ -75,6 +75,7 @@ Test-Suite Tests
                        Language.SQL.SimpleSQL.Oracle,
                        Language.SQL.SimpleSQL.QueryExprComponents,
                        Language.SQL.SimpleSQL.QueryExprs,
+                       Language.SQL.SimpleSQL.QueryExprParens,
                        Language.SQL.SimpleSQL.SQL2011Queries,
                        Language.SQL.SimpleSQL.SQL2011AccessControl,
                        Language.SQL.SimpleSQL.SQL2011Bits,

tests/Language/SQL/SimpleSQL/QueryExprParens.hs

@@ -0,0 +1,47 @@
+
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
+module Language.SQL.SimpleSQL.QueryExprParens (queryExprParensTests) where
+
+import Language.SQL.SimpleSQL.TestTypes
+import Language.SQL.SimpleSQL.Syntax
+import Language.SQL.SimpleSQL.TestRunners
+import Data.Text (Text)
+import qualified Text.RawString.QQ as R
+
+queryExprParensTests :: TestItem
+queryExprParensTests = Group "query expr parens"
+    [q "(select *  from t)" $ QueryExprParens $ ms "t"
+    ,q "select * from t except (select * from u except select * from v)"
+     $ (ms "t") `sexcept` QueryExprParens (ms "u" `sexcept` ms "v")
+        
+    ,q "(select * from t except select * from u) except select * from v"
+     $ QueryExprParens (ms "t" `sexcept` ms "u") `sexcept` ms "v"
+
+    ,q [R.r|
+select * from t
+union
+with a as (select * from u)
+select * from a
+|]
+     $ ms "t" `sunion` with [("a", ms "u")] (ms "a")
+
+    ,q [R.r|
+select * from t
+union
+(with a as (select * from u)
+ select * from a)
+|]
+     $ ms "t" `sunion` QueryExprParens (with [("a", ms "u")] (ms "a"))
+    ]
+  where
+    q :: HasCallStack => Text -> QueryExpr -> TestItem
+    q src ast = testQueryExpr ansi2011 src ast
+    ms t = toQueryExpr $ makeSelect
+            {msSelectList = [(Star,Nothing)]
+            ,msFrom = [TRSimple [Name Nothing t]]}
+    sexcept = so Except
+    sunion = so Union
+    so op a b = QueryExprSetOp a op SQDefault Respectively b
+    with es s =
+        With False (flip map es $ \(n,sn) -> (Alias (Name Nothing n) Nothing ,sn)) s

tests/Language/SQL/SimpleSQL/Tests.hs

@@ -25,6 +25,7 @@ import Language.SQL.SimpleSQL.GroupBy
 import Language.SQL.SimpleSQL.Postgres
 import Language.SQL.SimpleSQL.QueryExprComponents
 import Language.SQL.SimpleSQL.QueryExprs
+import Language.SQL.SimpleSQL.QueryExprParens
 import Language.SQL.SimpleSQL.TableRefs
 import Language.SQL.SimpleSQL.ScalarExprs
 import Language.SQL.SimpleSQL.Odbc
@@ -59,6 +60,7 @@ testData =
     ,odbcTests
     ,queryExprComponentTests
     ,queryExprsTests
+    ,queryExprParensTests
     ,tableRefTests
     ,groupByTests
     ,fullQueriesTests