Implement basic Lua output support

Ref #1700

Basic but working serialization to Lua tables.

cmd/utils.go

@@ -197,6 +197,8 @@ func createEncoder(format yqlib.PrinterOutputFormat) (yqlib.Encoder, error) {
 		return yqlib.NewTomlEncoder(), nil
 	case yqlib.ShellVariablesOutputFormat:
 		return yqlib.NewShellVariablesEncoder(), nil
+	case yqlib.LuaOutputFormat:
+		return yqlib.NewLuaEncoder(), nil
 	}
 	return nil, fmt.Errorf("invalid encoder: %v", format)
 }

pkg/yqlib/encoder_lua.go

@@ -0,0 +1,122 @@
+package yqlib
+
+import (
+	"io"
+	"strings"
+
+	yaml "gopkg.in/yaml.v3"
+)
+
+type luaEncoder struct {
+	docPrefix string
+	docSuffix string
+	escape    *strings.Replacer
+}
+
+func (le *luaEncoder) CanHandleAliases() bool {
+	return false
+}
+
+func NewLuaEncoder() Encoder {
+	escape := strings.NewReplacer("\n", "\\n", "\"", "\\\"", "\\", "\\\\")
+	return &luaEncoder{"return ", ";\n", escape}
+}
+
+func (le *luaEncoder) PrintDocumentSeparator(writer io.Writer) error {
+	return nil
+}
+
+func (le *luaEncoder) PrintLeadingContent(writer io.Writer, content string) error {
+	return nil
+}
+
+func (le *luaEncoder) encodeString(writer io.Writer, node *yaml.Node) error {
+	return writeString(writer, "\""+le.escape.Replace(node.Value)+"\"")
+}
+
+func (le *luaEncoder) encodeArray(writer io.Writer, node *yaml.Node) error {
+	err := writeString(writer, "{")
+	if err != nil {
+		return err
+	}
+	for _, child := range node.Content {
+		err := le.Encode(writer, child)
+		if err != nil {
+			return err
+		}
+		err = writeString(writer, ",")
+		if err != nil {
+			return err
+		}
+	}
+	return writeString(writer, "}")
+}
+
+func (le *luaEncoder) encodeMap(writer io.Writer, node *yaml.Node) error {
+	err := writeString(writer, "{")
+	if err != nil {
+		return err
+	}
+	for i, child := range node.Content {
+		if (i % 2) == 1 {
+			// value
+			err = le.Encode(writer, child)
+			if err != nil {
+				return err
+			}
+			err = writeString(writer, ";")
+			if err != nil {
+				return err
+			}
+		} else {
+			// key
+			err := writeString(writer, "[")
+			if err != nil {
+				return err
+			}
+			err = le.encodeAny(writer, child)
+			if err != nil {
+				return err
+			}
+			err = writeString(writer, "]=")
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return writeString(writer, "}")
+}
+
+func (le *luaEncoder) encodeAny(writer io.Writer, node *yaml.Node) error {
+	switch node.Kind {
+	case yaml.SequenceNode:
+		return le.encodeArray(writer, node)
+	case yaml.MappingNode:
+		return le.encodeMap(writer, node)
+	case yaml.ScalarNode:
+		switch node.Tag {
+		case "!!str":
+			return le.encodeString(writer, node)
+		case "!!null":
+			return writeString(writer, "nil")
+		default:
+			return writeString(writer, node.Value)
+		}
+	case yaml.DocumentNode:
+		err := writeString(writer, le.docPrefix)
+		if err != nil {
+			return err
+		}
+		err = le.encodeAny(writer, node.Content[0])
+		if err != nil {
+			return err
+		}
+		return writeString(writer, le.docSuffix)
+	default:
+		return writeString(writer, "nil --[[ encoder NYI -- "+node.ShortTag()+" ]]")
+	}
+}
+
+func (le *luaEncoder) Encode(writer io.Writer, node *yaml.Node) error {
+	return le.encodeAny(writer, node)
+}

pkg/yqlib/printer.go

@@ -33,6 +33,7 @@ const (
 	ShOutputFormat
 	TomlOutputFormat
 	ShellVariablesOutputFormat
+	LuaOutputFormat
 )
 
 func OutputFormatFromString(format string) (PrinterOutputFormat, error) {
@@ -53,8 +54,10 @@ func OutputFormatFromString(format string) (PrinterOutputFormat, error) {
 		return TomlOutputFormat, nil
 	case "shell", "s", "sh":
 		return ShellVariablesOutputFormat, nil
+	case "lua", "l":
+		return LuaOutputFormat, nil
 	default:
-		return 0, fmt.Errorf("unknown format '%v' please use [yaml|json|props|csv|tsv|xml|toml|shell]", format)
+		return 0, fmt.Errorf("unknown format '%v' please use [yaml|json|props|csv|tsv|xml|toml|shell|lua]", format)
 	}
 }