[#410] pkg/policy: Parse strings in filter key

With UN/LOCODE support, storage node may have
`UN-LOCODE` attribute. Policy parser should support
both `Ident` and `Strings` as filter keys to parse
rules such as `FILTER "UN-LOCODE" EQ "RU LED" AS F`.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/policy/grammar.ebnf

@@ -36,12 +36,15 @@ AndChain ::=
 
 Expr ::=
       '@' Ident		   (* filter reference *)
-    | Ident, Op, Value (* attribute filter *)
+    | Key, Op, Value (* attribute filter *)
 ;
 
 Op ::= 'EQ' | 'NE' | 'GE' | 'GT' | 'LT' | 'LE'
 ;
 
+Key ::= Ident | String
+;
+
 Value ::= Ident | Number | String
 ;
 

pkg/policy/grammar.go

@@ -52,7 +52,7 @@ type andChain struct {
 }
 
 type simpleExpr struct {
-	Key string `@Ident`
+	Key string `@(Ident | String)`
 	// We don't use literals here to improve error messages.
 	Op    string `@Ident`
 	Value string `@(Ident | String | Int)`

pkg/policy/query_test.go

@@ -235,6 +235,27 @@ func TestValidation(t *testing.T) {
 
 }
 
+func TestFilterStringSymbols(t *testing.T) {
+	q := `REP 1 IN S
+SELECT 1 FROM F AS S
+FILTER "UN-LOCODE" EQ "RU LED" AS F`
+
+	expected := new(netmap.PlacementPolicy)
+	expected.SetReplicas([]*netmap.Replica{
+		newReplica("S", 1),
+	})
+	expected.SetSelectors([]*netmap.Selector{
+		newSelector(1, netmap.UnspecifiedClause, "", "F", "S"),
+	})
+	expected.SetFilters([]*netmap.Filter{
+		newFilter("F", "UN-LOCODE", "RU LED", netmap.EQ),
+	})
+
+	r, err := Parse(q)
+	require.NoError(t, err)
+	require.EqualValues(t, expected, r)
+}
+
 func newFilter(name, key, value string, op netmap.Operation, sub ...*netmap.Filter) *netmap.Filter {
 	f := new(netmap.Filter)
 	f.SetName(name)