[#3] policy: allow to use brackets in filters

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/policy/doc.go

@@ -2,10 +2,7 @@
 //   ANTLRv4 grammar is provided in `parser/Query.g4` and `parser/QueryLexer.g4`.
 //
 // Current limitations:
-// 1. Grouping filter expressions in parenthesis is not supported right now.
-//    Requiring this will make query too verbose, making it optional makes
-//    our grammar not LL(1). This can be supported in future.
-// 2. Filters must be defined before they are used.
+// 1. Filters must be defined before they are used.
 // 	This requirement may be relaxed in future.
 //
 // Example query:

pkg/policy/parser/Query.g4

@@ -24,6 +24,7 @@ clause: CLAUSE_SAME | CLAUSE_DISTINCT; // nodes from distinct buckets
 filterExpr:
     F1 = filterExpr Op = AND_OP F2 = filterExpr
     | F1 = filterExpr Op = OR_OP F2 = filterExpr
+    | '(' Inner = filterExpr ')'
     | expr
     ;
 

pkg/policy/query.go

@@ -186,6 +186,10 @@ func (p *policyVisitor) VisitFilterExpr(ctx *parser.FilterExprContext) interface
 		return eCtx.Accept(p)
 	}
 
+	if inner := ctx.GetInner(); inner != nil {
+		return inner.Accept(p)
+	}
+
 	f := new(netmap.Filter)
 	op := operationFromString(ctx.GetOp().GetText())
 	f.SetOperation(op)

pkg/policy/query_test.go

@@ -215,6 +215,30 @@ FILTER City EQ "SPB" AND SSD EQ true OR City EQ "SPB" AND Rating GE 5 AS SPBSSD`
 	require.EqualValues(t, expected, r)
 }
 
+func TestBrackets(t *testing.T) {
+	q := `REP 7 IN SPB
+SELECT 1 IN City FROM SPBSSD AS SPB
+FILTER ( City EQ "SPB" OR SSD EQ true ) AND (City EQ "SPB" OR Rating GE 5) AS SPBSSD`
+
+	expected := new(netmap.PlacementPolicy)
+	expected.SetReplicas([]*netmap.Replica{newReplica("SPB", 7)})
+	expected.SetSelectors([]*netmap.Selector{
+		newSelector(1, netmap.UnspecifiedClause, "City", "SPBSSD", "SPB"),
+	})
+	expected.SetFilters([]*netmap.Filter{
+		newFilter("SPBSSD", "", "", netmap.AND,
+			newFilter("", "", "", netmap.OR,
+				newFilter("", "City", "SPB", netmap.EQ),
+				newFilter("", "SSD", "true", netmap.EQ)),
+			newFilter("", "", "", netmap.OR,
+				newFilter("", "City", "SPB", netmap.EQ),
+				newFilter("", "Rating", "5", netmap.GE)))})
+
+	r, err := Parse(q)
+	require.NoError(t, err)
+	require.EqualValues(t, expected, r)
+}
+
 func TestValidation(t *testing.T) {
 	t.Run("MissingSelector", func(t *testing.T) {
 		q := `REP 3 IN RU`