[#3] policy: use ANTLRv4 parser generator

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

.gitattributes

@@ -0,0 +1,4 @@
+/pkg/policy/parser/*.go -diff
+/pkg/policy/parser/generate.go diff
+**/*.interp -diff
+**/*.tokens -diff

go.mod

@@ -3,7 +3,7 @@ module github.com/nspcc-dev/neofs-sdk-go
 go 1.16
 
 require (
-	github.com/alecthomas/participle v0.7.1
+	github.com/antlr/antlr4/runtime/Go/antlr v0.0.0-20210521073959-f0d4d129b7f1
 	github.com/nspcc-dev/neofs-api-go v1.27.0
 	github.com/stretchr/testify v1.6.1
 	go.uber.org/zap v1.10.0

go.sum

@@ -10,15 +10,14 @@ github.com/Workiva/go-datastructures v1.0.50/go.mod h1:Z+F2Rca0qCsVYDS8z7bAGm8f3
 github.com/abiosoft/ishell v2.0.0+incompatible/go.mod h1:HQR9AqF2R3P4XXpMpI0NAzgHf/aS6+zVXRj14cVk9qg=
 github.com/abiosoft/readline v0.0.0-20180607040430-155bce2042db/go.mod h1:rB3B4rKii8V21ydCbIzH5hZiCQE7f5E9SzUb/ZZx530=
 github.com/aead/siphash v1.0.1/go.mod h1:Nywa3cDsYNNK3gaciGTWPwHt0wlpNV15vwmswBAUSII=
-github.com/alecthomas/participle v0.7.1 h1:2bN7reTw//5f0cugJcTOnY/NYZcWQOaajW+BwZB5xWs=
-github.com/alecthomas/participle v0.7.1/go.mod h1:HfdmEuwvr12HXQN44HPWXR0lHmVolVYe4dyL6lQ3duY=
-github.com/alecthomas/repr v0.0.0-20181024024818-d37bc2a10ba1/go.mod h1:xTS7Pm1pD1mvyM075QCDSRqH6qRLXylzS24ZTpRiSzQ=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/template v0.0.0-20190718012654-fb15b899a751/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
 github.com/alecthomas/units v0.0.0-20190717042225-c3de453c63f4/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
 github.com/alicebob/gopher-json v0.0.0-20180125190556-5a6b3ba71ee6/go.mod h1:SGnFV6hVsYE877CKEZ6tDNTjaSXYUk6QqoIK6PrAtcc=
 github.com/alicebob/miniredis v2.5.0+incompatible/go.mod h1:8HZjEj4yU0dwhYHky+DxYx+6BMjkBbe5ONFIF1MXffk=
+github.com/antlr/antlr4/runtime/Go/antlr v0.0.0-20210521073959-f0d4d129b7f1 h1:zFRi26YWd7NIorBXe8UkevRl0dIvk/AnXHWaAiZG+Yk=
+github.com/antlr/antlr4/runtime/Go/antlr v0.0.0-20210521073959-f0d4d129b7f1/go.mod h1:F7bn7fEU90QkQ3tnmaTx3LTKLEDqnwWODIYppRQ5hnY=
 github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6/go.mod h1:grANhF5doyWs3UAsr3K4I6qtAmlQcZDesFNEHPZAzj8=
 github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973/go.mod h1:Dwedo/Wpr24TaqPxmxbtue+5NUziq4I4S80YR8gNf3Q=
 github.com/beorn7/perks v1.0.0/go.mod h1:KWe93zE9D1o94FZ5RNwFwVgaQK1VOXiVxmqh+CedLV8=

pkg/policy/doc.go

@@ -1,5 +1,5 @@
 // Package policy provides facilities for creating policy from SQL-like language.
-//   eBNF grammar is provided in `grammar.ebnf` for illustration.
+//   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.

pkg/policy/grammar.ebnf

@@ -1,55 +0,0 @@
-Policy ::=
-    RepStmt, [RepStmt],
-    CbtStmt?,
-    [SelectStmt],
-    [FilterStmt],
-;
-
-RepStmt ::=
-    'REP', Number1, (* number of object replicas *)
-    ('AS', Ident)?  (* optional selector name *)
-;
-
-CbtStmt ::= 'CBF', Number1 (* container backup factor *)
-;
-
-SelectStmt ::=
-    'SELECT', Number1,    (* number of nodes to select without container backup factor *)
-    ('IN', Clause?, Ident)?, (* bucket name *)
-    FROM, (Ident | '*'),  (* filter reference or whole netmap *)
-    ('AS', Ident)?        (* optional selector name *)
-;
-
-Clause ::=
-      'SAME'     (* nodes from the same bucket *)
-    | 'DISTINCT' (* nodes from distinct buckets *)
-;
-
-FilterStmt ::=
-    'FILTER', AndChain, ['OR', AndChain],
-    'AS', Ident (* obligatory filter name *)
-;
-
-AndChain ::=
-    Expr, ['AND', Expr]
-;
-
-Expr ::=
-      '@' Ident		   (* filter reference *)
-    | Key, Op, Value (* attribute filter *)
-;
-
-Op ::= 'EQ' | 'NE' | 'GE' | 'GT' | 'LT' | 'LE'
-;
-
-Key ::= Ident | String
-;
-
-Value ::= Ident | Number | String
-;
-
-Number1 ::= Digit1 [Digit];
-Number ::= Digit [Digit];
-
-Digit1 ::= '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' ;
-Digit ::= '0' | Digit1;

pkg/policy/grammar.go

@@ -1,60 +0,0 @@
-//nolint:govet,golint // fails on struct tags here, but participle needs this syntax
-package policy
-
-import (
-	"github.com/alecthomas/participle"
-)
-
-var parser *participle.Parser
-
-func init() {
-	p, err := participle.Build(&query{})
-	if err != nil {
-		panic(err)
-	}
-	parser = p
-}
-
-type query struct {
-	Replicas  []*replicaStmt  `@@+`
-	CBF       uint32          `("CBF" @Int)?`
-	Selectors []*selectorStmt `@@*`
-	Filters   []*filterStmt   `@@*`
-}
-
-type replicaStmt struct {
-	Count    int    `"REP" @Int`
-	Selector string `("IN" @Ident)?`
-}
-
-type selectorStmt struct {
-	Count  uint32   `"SELECT" @Int`
-	Bucket []string `("IN" @(("SAME" | "DISTINCT")? Ident))?`
-	Filter string   `"FROM" @(Ident | "*")`
-	Name   string   `("AS" @Ident)?`
-}
-
-type filterStmt struct {
-	Value *orChain `"FILTER" @@`
-	Name  string   `"AS" @Ident`
-}
-
-type filterOrExpr struct {
-	Reference string      `"@"@Ident`
-	Expr      *simpleExpr `| @@`
-}
-
-type orChain struct {
-	Clauses []*andChain `@@ ("OR" @@)*`
-}
-
-type andChain struct {
-	Clauses []*filterOrExpr `@@ ("AND" @@)*`
-}
-
-type simpleExpr struct {
-	Key string `@(Ident | String)`
-	// We don't use literals here to improve error messages.
-	Op    string `@Ident`
-	Value string `@(Ident | String | Int)`
-}

pkg/policy/parser/Query.g4

@@ -0,0 +1,45 @@
+parser grammar Query;
+
+options {
+    tokenVocab = QueryLexer;
+}
+
+policy: repStmt+ cbfStmt? selectStmt* filterStmt*;
+
+repStmt:
+    REP Count = NUMBER1     // number of object replicas
+    (IN Selector = ident)?; // optional selector name
+
+cbfStmt: CBF BackupFactor = NUMBER1; // container backup factor
+
+selectStmt:
+    SELECT Count = NUMBER1       // number of nodes to select without container backup factor *)
+    (IN clause? Bucket = ident)? // bucket name
+    FROM Filter = identWC        // filter reference or whole netmap
+    (AS Name = ident)?           // optional selector name
+    ;
+
+clause: CLAUSE_SAME | CLAUSE_DISTINCT; // nodes from distinct buckets
+
+filterExpr:
+    F1 = filterExpr Op = AND_OP F2 = filterExpr
+    | F1 = filterExpr Op = OR_OP F2 = filterExpr
+    | expr
+    ;
+
+filterStmt:
+    FILTER Expr = filterExpr
+    AS Name = ident // obligatory filter name
+    ;
+
+expr:
+    AT Filter = ident                               // reference to named filter
+    | Key = filterKey SIMPLE_OP Value = filterValue // attribute comparison
+    ;
+
+filterKey : ident | STRING;
+filterValue : ident | number | STRING;
+number : ZERO | NUMBER1;
+keyword : REP | IN | AS | SELECT | FROM | FILTER;
+ident : keyword | IDENT;
+identWC : ident | WILDCARD;

pkg/policy/parser/QueryLexer.g4

@@ -0,0 +1,41 @@
+lexer grammar QueryLexer;
+
+AND_OP     : 'AND';
+OR_OP      : 'OR';
+SIMPLE_OP  : 'EQ' | 'NE' | 'GE' | 'GT' | 'LT' | 'LE';
+
+REP      : 'REP';
+IN       : 'IN';
+AS       : 'AS';
+CBF      : 'CBF';
+SELECT   : 'SELECT';
+FROM     : 'FROM';
+FILTER   : 'FILTER';
+WILDCARD : '*';
+
+CLAUSE_SAME     : 'SAME';
+CLAUSE_DISTINCT : 'DISTINCT';
+
+L_PAREN : '(';
+R_PAREN : ')';
+AT      : '@';
+
+IDENT             : Nondigit (Digit | Nondigit)* ;
+fragment Digit    : [0-9] ;
+fragment Nondigit : [a-zA-Z_] ;
+
+NUMBER1 : [1-9] Digit* ;
+ZERO    : '0' ;
+
+// Taken from antlr4 json grammar with minor corrections.
+// https://github.com/antlr/grammars-v4/blob/master/json/JSON.g4
+STRING : '"'  (ESC | SAFECODEPOINTDOUBLE)* '"'
+       | '\'' (ESC | SAFECODEPOINTSINGLE)* '\'' ;
+
+fragment ESC : '\\' (['"\\/bfnrt] | UNICODE) ;
+fragment UNICODE : 'u' HEX HEX HEX HEX ;
+fragment HEX : [0-9a-fA-F] ;
+fragment SAFECODEPOINTSINGLE : ~ ['\\\u0000-\u001F] ;
+fragment SAFECODEPOINTDOUBLE : ~ ["\\\u0000-\u001F] ;
+
+WS : [ \t\n\r] + -> skip ;

pkg/policy/parser/generate.go

@@ -0,0 +1,3 @@
+package parser
+
+//go:generate antlr4 -Dlanguage=Go -visitor QueryLexer.g4 Query.g4

pkg/policy/query.go

@@ -3,9 +3,12 @@ package policy
 import (
 	"errors"
 	"fmt"
+	"strconv"
 	"strings"
 
+	"github.com/antlr/antlr4/runtime/Go/antlr"
 	"github.com/nspcc-dev/neofs-api-go/pkg/netmap"
+	"github.com/nspcc-dev/neofs-sdk-go/pkg/policy/parser"
 )
 
 var (
@@ -19,83 +22,252 @@ var (
 	ErrUnknownFilter = errors.New("policy: filter not found")
 	// ErrUnknownSelector is returned when a value of IN is unknown.
 	ErrUnknownSelector = errors.New("policy: selector not found")
+	// ErrSyntaxError is returned for errors found by ANTLR parser.
+	ErrSyntaxError = errors.New("policy: syntax error")
 )
 
-func parse(s string) (*query, error) {
+type policyVisitor struct {
-	q := new(query)
+	errors []error
-	err := parser.Parse(strings.NewReader(s), q)
+	parser.BaseQueryVisitor
-	if err != nil {
+	antlr.DefaultErrorListener
-		return nil, err
-	}
-	return q, nil
 }
 
 // Parse parses s into a placement policy.
 func Parse(s string) (*netmap.PlacementPolicy, error) {
-	q, err := parse(s)
+	return parse(s)
-	if err != nil {
+}
+
+func newPolicyVisitor() *policyVisitor {
+	return &policyVisitor{}
+}
+
+func parse(s string) (*netmap.PlacementPolicy, error) {
+	input := antlr.NewInputStream(s)
+	lexer := parser.NewQueryLexer(input)
+	stream := antlr.NewCommonTokenStream(lexer, 0)
+
+	p := parser.NewQuery(stream)
+	p.BuildParseTrees = true
+
+	v := newPolicyVisitor()
+	p.RemoveErrorListeners()
+	p.AddErrorListener(v)
+	pl := p.Policy().Accept(v)
+
+	if len(v.errors) != 0 {
+		return nil, v.errors[0]
+	}
+	if err := validatePolicy(pl.(*netmap.PlacementPolicy)); err != nil {
 		return nil, err
 	}
+	return pl.(*netmap.PlacementPolicy), nil
+}
 
-	seenFilters := map[string]bool{}
+func (p *policyVisitor) SyntaxError(recognizer antlr.Recognizer, offendingSymbol interface{}, line, column int, msg string, e antlr.RecognitionException) {
-	fs := make([]*netmap.Filter, 0, len(q.Filters))
+	p.reportError(fmt.Errorf("%w: line %d:%d %s", ErrSyntaxError, line, column, msg))
-	for _, qf := range q.Filters {
+}
-		f, err := filterFromOrChain(qf.Value, seenFilters)
+
-		if err != nil {
+func (p *policyVisitor) reportError(err error) interface{} {
-			return nil, err
+	p.errors = append(p.errors, err)
+	return nil
+}
+
+// VisitPolicy implements parser.QueryVisitor interface.
+func (p *policyVisitor) VisitPolicy(ctx *parser.PolicyContext) interface{} {
+	if len(p.errors) != 0 {
+		return nil
+	}
+
+	pl := new(netmap.PlacementPolicy)
+
+	repStmts := ctx.AllRepStmt()
+	rs := make([]*netmap.Replica, 0, len(repStmts))
+	for _, r := range repStmts {
+		res, ok := r.Accept(p).(*netmap.Replica)
+		if !ok {
+			return nil
 		}
-		f.SetName(qf.Name)
+
-		fs = append(fs, f)
+		rs = append(rs, res)
-		seenFilters[qf.Name] = true
+	}
+	pl.SetReplicas(rs...)
+
+	if cbfStmt := ctx.CbfStmt(); cbfStmt != nil {
+		cbf, ok := cbfStmt.(*parser.CbfStmtContext).Accept(p).(uint32)
+		if !ok {
+			return nil
+		}
+		pl.SetContainerBackupFactor(cbf)
+	}
+
+	selStmts := ctx.AllSelectStmt()
+	ss := make([]*netmap.Selector, 0, len(selStmts))
+	for _, s := range selStmts {
+		res, ok := s.Accept(p).(*netmap.Selector)
+		if !ok {
+			return nil
+		}
+
+		ss = append(ss, res)
+	}
+	pl.SetSelectors(ss...)
+
+	filtStmts := ctx.AllFilterStmt()
+	fs := make([]*netmap.Filter, 0, len(filtStmts))
+	for _, f := range filtStmts {
+		fs = append(fs, f.Accept(p).(*netmap.Filter))
+	}
+	pl.SetFilters(fs...)
+
+	return pl
+}
+
+func (p *policyVisitor) VisitCbfStmt(ctx *parser.CbfStmtContext) interface{} {
+	cbf, err := strconv.ParseUint(ctx.GetBackupFactor().GetText(), 10, 32)
+	if err != nil {
+		return p.reportError(ErrInvalidNumber)
+	}
+
+	return uint32(cbf)
+}
+
+// VisitRepStmt implements parser.QueryVisitor interface.
+func (p *policyVisitor) VisitRepStmt(ctx *parser.RepStmtContext) interface{} {
+	num, err := strconv.ParseUint(ctx.GetCount().GetText(), 10, 32)
+	if err != nil {
+		return p.reportError(ErrInvalidNumber)
+	}
+
+	rs := new(netmap.Replica)
+	rs.SetCount(uint32(num))
+
+	if sel := ctx.GetSelector(); sel != nil {
+		rs.SetSelector(sel.GetText())
+	}
+
+	return rs
+}
+
+// VisitSelectStmt implements parser.QueryVisitor interface.
+func (p *policyVisitor) VisitSelectStmt(ctx *parser.SelectStmtContext) interface{} {
+	res, err := strconv.ParseUint(ctx.GetCount().GetText(), 10, 32)
+	if err != nil {
+		return p.reportError(ErrInvalidNumber)
+	}
+
+	s := new(netmap.Selector)
+	s.SetCount(uint32(res))
+
+	if clStmt := ctx.Clause(); clStmt != nil {
+		s.SetClause(clauseFromString(clStmt.GetText()))
+	}
+
+	if bStmt := ctx.GetBucket(); bStmt != nil {
+		s.SetAttribute(ctx.GetBucket().GetText())
+	}
+
+	s.SetFilter(ctx.GetFilter().GetText()) // either ident or wildcard
+
+	if ctx.AS() != nil {
+		s.SetName(ctx.GetName().GetText())
+	}
+	return s
+}
+
+// VisitFilterStmt implements parser.QueryVisitor interface.
+func (p *policyVisitor) VisitFilterStmt(ctx *parser.FilterStmtContext) interface{} {
+	f := p.VisitFilterExpr(ctx.GetExpr().(*parser.FilterExprContext)).(*netmap.Filter)
+	f.SetName(ctx.GetName().GetText())
+	return f
+}
+
+func (p *policyVisitor) VisitFilterExpr(ctx *parser.FilterExprContext) interface{} {
+	if eCtx := ctx.Expr(); eCtx != nil {
+		return eCtx.Accept(p)
+	}
+
+	f := new(netmap.Filter)
+	op := operationFromString(ctx.GetOp().GetText())
+	f.SetOperation(op)
+
+	f1 := ctx.GetF1().Accept(p).(*netmap.Filter)
+	f2 := ctx.GetF2().Accept(p).(*netmap.Filter)
+
+	// Consider f1=(.. AND ..) AND f2. This can be merged because our AND operation
+	// is of arbitrary arity. ANTLR generates left-associative parse-tree by default.
+	if f1.Operation() == op {
+		f.SetInnerFilters(append(f1.InnerFilters(), f2)...)
+		return f
+	}
+
+	f.SetInnerFilters(f1, f2)
+	return f
+}
+
+// VisitFilterKey implements parser.QueryVisitor interface.
+func (p *policyVisitor) VisitFilterKey(ctx *parser.FilterKeyContext) interface{} {
+	if id := ctx.Ident(); id != nil {
+		return id.GetText()
+	}
+
+	str := ctx.STRING().GetText()
+	return str[1 : len(str)-1]
+}
+
+func (p *policyVisitor) VisitFilterValue(ctx *parser.FilterValueContext) interface{} {
+	if id := ctx.Ident(); id != nil {
+		return id.GetText()
+	}
+
+	if num := ctx.Number(); num != nil {
+		return num.GetText()
+	}
+
+	str := ctx.STRING().GetText()
+	return str[1 : len(str)-1]
+}
+
+// VisitExpr implements parser.QueryVisitor interface.
+func (p *policyVisitor) VisitExpr(ctx *parser.ExprContext) interface{} {
+	f := new(netmap.Filter)
+	if flt := ctx.GetFilter(); flt != nil {
+		f.SetName(flt.GetText())
+		return f
+	}
+
+	key := ctx.GetKey().Accept(p)
+	opStr := ctx.SIMPLE_OP().GetText()
+	value := ctx.GetValue().Accept(p)
+
+	f.SetKey(key.(string))
+	f.SetOperation(operationFromString(opStr))
+	f.SetValue(value.(string))
+	return f
+}
+
+// validatePolicy checks high-level constraints such as filter link in SELECT
+// being actually defined in FILTER section.
+func validatePolicy(p *netmap.PlacementPolicy) error {
+	seenFilters := map[string]bool{}
+	for _, f := range p.Filters() {
+		seenFilters[f.Name()] = true
 	}
 
 	seenSelectors := map[string]bool{}
-	ss := make([]*netmap.Selector, 0, len(q.Selectors))
+	for _, s := range p.Selectors() {
-	for _, qs := range q.Selectors {
+		if flt := s.Filter(); flt != netmap.MainFilterName && !seenFilters[flt] {
-		if qs.Filter != netmap.MainFilterName && !seenFilters[qs.Filter] {
+			return fmt.Errorf("%w: '%s'", ErrUnknownFilter, flt)
-			return nil, fmt.Errorf("%w: '%s'", ErrUnknownFilter, qs.Filter)
 		}
-		s := netmap.NewSelector()
+		seenSelectors[s.Name()] = true
-		switch len(qs.Bucket) {
-		case 1: // only bucket
-			s.SetAttribute(qs.Bucket[0])
-		case 2: // clause + bucket
-			s.SetClause(clauseFromString(qs.Bucket[0]))
-			s.SetAttribute(qs.Bucket[1])
-		}
-		s.SetName(qs.Name)
-		seenSelectors[qs.Name] = true
-		s.SetFilter(qs.Filter)
-		if qs.Count == 0 {
-			return nil, fmt.Errorf("%w: SELECT", ErrInvalidNumber)
-		}
-		s.SetCount(qs.Count)
-		ss = append(ss, s)
 	}
 
-	rs := make([]*netmap.Replica, 0, len(q.Replicas))
+	for _, r := range p.Replicas() {
-	for _, qr := range q.Replicas {
+		if sel := r.Selector(); sel != "" && !seenSelectors[sel] {
-		r := netmap.NewReplica()
+			return fmt.Errorf("%w: '%s'", ErrUnknownSelector, sel)
-		if qr.Selector != "" {
-			if !seenSelectors[qr.Selector] {
-				return nil, fmt.Errorf("%w: '%s'", ErrUnknownSelector, qr.Selector)
-			}
-			r.SetSelector(qr.Selector)
 		}
-		if qr.Count == 0 {
-			return nil, fmt.Errorf("%w: REP", ErrInvalidNumber)
-		}
-		r.SetCount(uint32(qr.Count))
-		rs = append(rs, r)
 	}
 
-	p := new(netmap.PlacementPolicy)
+	return nil
-	p.SetFilters(fs...)
-	p.SetSelectors(ss...)
-	p.SetReplicas(rs...)
-	p.SetContainerBackupFactor(q.CBF)
-
-	return p, nil
 }
 
 func clauseFromString(s string) netmap.Clause {
@@ -105,74 +277,31 @@ func clauseFromString(s string) netmap.Clause {
 	case "DISTINCT":
 		return netmap.ClauseDistinct
 	default:
-		return 0
+		// Such errors should be handled by ANTLR code thus this panic.
+		panic(fmt.Errorf("BUG: invalid clause: %s", s))
 	}
 }
 
-func filterFromOrChain(expr *orChain, seen map[string]bool) (*netmap.Filter, error) {
+func operationFromString(op string) netmap.Operation {
-	var fs []*netmap.Filter
+	switch strings.ToUpper(op) {
-	for _, ac := range expr.Clauses {
+	case "AND":
-		f, err := filterFromAndChain(ac, seen)
+		return netmap.OpAND
-		if err != nil {
+	case "OR":
-			return nil, err
+		return netmap.OpOR
-		}
-		fs = append(fs, f)
-	}
-	if len(fs) == 1 {
-		return fs[0], nil
-	}
-
-	f := netmap.NewFilter()
-	f.SetOperation(netmap.OpOR)
-	f.SetInnerFilters(fs...)
-	return f, nil
-}
-
-func filterFromAndChain(expr *andChain, seen map[string]bool) (*netmap.Filter, error) {
-	var fs []*netmap.Filter
-	for _, fe := range expr.Clauses {
-		var f *netmap.Filter
-		var err error
-		if fe.Expr != nil {
-			f, err = filterFromSimpleExpr(fe.Expr, seen)
-		} else {
-			f = netmap.NewFilter()
-			f.SetName(fe.Reference)
-		}
-		if err != nil {
-			return nil, err
-		}
-		fs = append(fs, f)
-	}
-	if len(fs) == 1 {
-		return fs[0], nil
-	}
-
-	f := netmap.NewFilter()
-	f.SetOperation(netmap.OpAND)
-	f.SetInnerFilters(fs...)
-	return f, nil
-}
-
-func filterFromSimpleExpr(se *simpleExpr, seen map[string]bool) (*netmap.Filter, error) {
-	f := netmap.NewFilter()
-	f.SetKey(se.Key)
-	switch se.Op {
 	case "EQ":
-		f.SetOperation(netmap.OpEQ)
+		return netmap.OpEQ
 	case "NE":
-		f.SetOperation(netmap.OpNE)
+		return netmap.OpNE
 	case "GE":
-		f.SetOperation(netmap.OpGE)
+		return netmap.OpGE
 	case "GT":
-		f.SetOperation(netmap.OpGT)
+		return netmap.OpGT
 	case "LE":
-		f.SetOperation(netmap.OpLE)
+		return netmap.OpLE
 	case "LT":
-		f.SetOperation(netmap.OpLT)
+		return netmap.OpLT
 	default:
-		return nil, fmt.Errorf("%w: '%s'", ErrUnknownOp, se.Op)
+		// Such errors should be handled by ANTLR code thus this panic.
+		panic(fmt.Errorf("BUG: invalid operation: %s", op))
 	}
-	f.SetValue(se.Value)
-	return f, nil
 }

pkg/policy/query_test.go

@@ -2,6 +2,7 @@ package policy
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 
 	"github.com/nspcc-dev/neofs-api-go/v2/netmap"
@@ -80,6 +81,32 @@ func TestFromSelectNoAttribute(t *testing.T) {
 	})
 }
 
+func TestString(t *testing.T) {
+	qTemplate := `REP 1
+SELECT 1 IN City FROM Filt
+FILTER Property EQ %s AND Something NE 7 AS Filt`
+
+	testCases := []string{
+		`"double-quoted"`,
+		`"with ' single"`,
+		`'single-quoted'`,
+		`'with " double'`,
+	}
+
+	for _, s := range testCases {
+		t.Run(s, func(t *testing.T) {
+			q := fmt.Sprintf(qTemplate, s)
+			r, err := Parse(q)
+			require.NoError(t, err)
+
+			expected := newFilter("Filt", "", "", netmap.AND,
+				newFilter("", "Property", s[1:len(s)-1], netmap.EQ),
+				newFilter("", "Something", "7", netmap.NE))
+			require.EqualValues(t, []*netmap.Filter{expected}, r.Filters())
+		})
+	}
+}
+
 func TestFromSelectClause(t *testing.T) {
 	q := `REP 4
 SELECT 3 IN Country FROM *
@@ -205,12 +232,12 @@ func TestValidation(t *testing.T) {
               SELECT 1 IN City FROM F
 			  FILTER Country KEK RU AS F`
 		_, err := Parse(q)
-		require.True(t, errors.Is(err, ErrUnknownOp), "got: %v", err)
+		require.True(t, errors.Is(err, ErrSyntaxError), "got: %v", err)
 	})
 	t.Run("TypoInREP", func(t *testing.T) {
 		q := `REK 3`
 		_, err := Parse(q)
-		require.Error(t, err)
+		require.True(t, errors.Is(err, ErrSyntaxError))
 	})
 	t.Run("InvalidFilterName", func(t *testing.T) {
 		q := `REP 3
@@ -223,13 +250,13 @@ func TestValidation(t *testing.T) {
 	t.Run("InvalidNumberInREP", func(t *testing.T) {
 		q := `REP 0`
 		_, err := Parse(q)
-		require.True(t, errors.Is(err, ErrInvalidNumber), "got: %v", err)
+		require.True(t, errors.Is(err, ErrSyntaxError), "got: %v", err)
 	})
 	t.Run("InvalidNumberInREP", func(t *testing.T) {
 		q := `REP 1 IN Good
 			  SELECT 0 IN City FROM *`
 		_, err := Parse(q)
-		require.True(t, errors.Is(err, ErrInvalidNumber), "got: %v", err)
+		require.True(t, errors.Is(err, ErrSyntaxError), "got: %v", err)
 	})
 }