compiler: allow to convert string constants to []byte

Also load constant directly into stack, not by name.

pkg/compiler/byte_conversion_test.go

@@ -54,3 +54,28 @@ func TestByteConversionDirectlyInFunctionCall(t *testing.T) {
 	`
 	eval(t, src, []byte("foo"))
 }
+
+func TestByteConversionOfConstant(t *testing.T) {
+	src := `
+	package foo
+	const foo = "foo"
+	func Main() []byte {
+		b := []byte(foo)
+		return b
+	}
+	`
+	eval(t, src, []byte("foo"))
+}
+
+func TestByteConversionOfVariable(t *testing.T) {
+	src := `
+	package foo
+	func Main() []byte {
+		a := "fo"
+		a = a + "o"
+		b := []byte(a)
+		return b
+	}
+	`
+	eval(t, src, []byte("foo"))
+}

pkg/compiler/codegen.go

@@ -349,6 +349,8 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 				return nil
 			}
 			c.emitLoadConst(value)
+		} else if tv := c.typeInfo.Types[n]; tv.Value != nil {
+			c.emitLoadConst(tv)
 		} else {
 			c.emitLoadLocal(n.Name)
 		}
@@ -481,11 +483,9 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 				return nil
 			}
 		case *ast.ArrayType:
-			// For now we will assume that there is only 1 argument passed which
-			// will be a basic literal (string kind). This only to handle string
-			// to byte slice conversions. E.G. []byte("foobar")
-			arg := n.Args[0].(*ast.BasicLit)
-			c.emitLoadConst(c.typeInfo.Types[arg])
+			// For now we will assume that there are only byte slice conversions.
+			// E.g. []byte("foobar") or []byte(scriptHash).
+			ast.Walk(c, n.Args[0])
 			return nil
 		}