pkg/compiler: allow use of empty strings

This comes up in several contexts in netfilter.

6 files changed, 10 insertions, 13 deletions

diff --git a/pkg/ast/ast.go b/pkg/ast/ast.go
index 08703ba33..f7d5b8b32 100644
--- a/pkg/ast/ast.go
+++ b/pkg/ast/ast.go
@@ -185,10 +185,11 @@ func (n *Int) Info() (Pos, string, string) {
 type Type struct {
 	Pos Pos
 	// Only one of Value, Ident, String is filled.
-	Value    uint64
-	ValueHex bool
-	Ident    string
-	String   string
+	Value     uint64
+	ValueHex  bool
+	Ident     string
+	String    string
+	HasString bool
 	// Part after COLON (for ranges and bitfields).
 	HasColon  bool
 	Pos2      Pos
diff --git a/pkg/ast/clone.go b/pkg/ast/clone.go
index b915c1f33..b754b7650 100644
--- a/pkg/ast/clone.go
+++ b/pkg/ast/clone.go
@@ -182,6 +182,7 @@ func (n *Type) Clone() Node {
 		ValueHex:  n.ValueHex,
 		Ident:     n.Ident,
 		String:    n.String,
+		HasString: n.HasString,
 		HasColon:  n.HasColon,
 		Pos2:      n.Pos2,
 		Value2:    n.Value2,
diff --git a/pkg/ast/format.go b/pkg/ast/format.go
index c1dd3a624..a7e0f568f 100644
--- a/pkg/ast/format.go
+++ b/pkg/ast/format.go
@@ -152,7 +152,7 @@ func fmtType(t *Type) string {
 	switch {
 	case t.Ident != "":
 		v = t.Ident
-	case t.String != "":
+	case t.HasString:
 		v = fmt.Sprintf("\"%v\"", t.String)
 	default:
 		v = fmtIntValue(t.Value, t.ValueHex)
diff --git a/pkg/ast/parser.go b/pkg/ast/parser.go
index bd5650ad5..a7cfdbf02 100644
--- a/pkg/ast/parser.go
+++ b/pkg/ast/parser.go
@@ -419,6 +419,7 @@ func (p *parser) parseType() *Type {
 		arg.Ident = p.lit
 	case tokString:
 		arg.String = p.lit
+		arg.HasString = true
 	default:
 		p.expect(tokInt, tokIdent, tokString)
 	}
diff --git a/pkg/ast/scanner.go b/pkg/ast/scanner.go
index bd2171506..5ad5e5808 100644
--- a/pkg/ast/scanner.go
+++ b/pkg/ast/scanner.go
@@ -177,12 +177,6 @@ func (s *scanner) Scan() (tok token, lit string, pos Pos) {
 				break
 			}
 		}
-		if lit == "" {
-			// Currently unsupported because with the current Type representation
-			// it would not be possible to understand if it is an empty string
-			// or a 0 integer.
-			s.Error(pos, "empty string literals are not supported")
-		}
 		s.next()
 	case s.ch >= '0' && s.ch <= '9':
 		tok = tokInt
diff --git a/pkg/ast/testdata/all.txt b/pkg/ast/testdata/all.txt
index d4452b34f..ede11a88a 100644
--- a/pkg/ast/testdata/all.txt
+++ b/pkg/ast/testdata/all.txt
@@ -25,10 +25,10 @@ define FOO `bar				### C expression is not terminated
 foo(x int32[1:2:3, opt])		### unexpected ':', expecting ']'
 
 s0 {
-	f0	string[""]		### empty string literals are not supported
+	f0	string[""]
 }
 
-sf0 = "", "1"				### empty string literals are not supported
+sf0 = "", "1"
 
 include <linux/foo.h>
 include "linux/foo.h"