compiler: allow for loops with empty condition

pkg/compiler/codegen.go

@@ -781,10 +781,12 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 		// Set label and walk the condition.
 		c.pushStackLabel(label, 0)
 		c.setLabel(fstart)
-		ast.Walk(c, n.Cond)
+		if n.Cond != nil {
+			ast.Walk(c, n.Cond)
 
-		// Jump if the condition is false
+			// Jump if the condition is false
-		emit.Jmp(c.prog.BinWriter, opcode.JMPIFNOT, fend)
+			emit.Jmp(c.prog.BinWriter, opcode.JMPIFNOT, fend)
+		}
 
 		// Walk body followed by the iterator (post stmt).
 		ast.Walk(c, n.Body)

pkg/compiler/for_test.go

@@ -374,6 +374,23 @@ func TestDec(t *testing.T) {
 	eval(t, src, big.NewInt(1))
 }
 
+func TestForLoopEmpty(t *testing.T) {
+	src := `
+	package foo
+	func Main() int {
+		x := 0
+		for {
+			x++
+			if x == 2 {
+				break
+			}
+		}
+		return x
+	}
+	`
+	eval(t, src, big.NewInt(2))
+}
+
 func TestForLoopBigIter(t *testing.T) {
 	src := `
 	package foo