printer: add skeleton printer package

Author: haya14busa

printer/printer.go

@@ -0,0 +1,67 @@
+// Package printer implements printing of AST nodes.
+//
+// This is WIP package. DO NOT USE.
+package printer
+
+import (
+	"errors"
+	"fmt"
+	"io"
+
+	"github.com/haya14busa/go-vimlparser/ast"
+)
+
+// A Config node controls the output of Fprint.
+type Config struct{}
+
+// Fprint "pretty-prints" an AST node to output for a given configuration cfg.
+func Fprint(output io.Writer, node ast.Node, cfg *Config) error {
+	var p printer
+	p.init(cfg)
+	if err := p.printNode(node); err != nil {
+		return err
+	}
+	if _, err := output.Write(p.output); err != nil {
+		return err
+	}
+	return nil
+}
+
+type printer struct {
+	Config
+
+	// Current state
+	output []byte // raw printer result
+}
+
+func (p *printer) init(cfg *Config) {
+	if cfg == nil {
+		cfg = &Config{}
+	}
+	p.Config = *cfg
+}
+
+func (p *printer) printNode(node ast.Node) error {
+	switch n := node.(type) {
+	case *ast.File:
+		return p.file(n)
+	case ast.Expr:
+		return p.expr(n)
+	case ast.Statement:
+		return p.stmt(n)
+	default:
+		return fmt.Errorf("go-vimlparser/printer: unsupported node type %T", node)
+	}
+}
+
+func (p *printer) file(f *ast.File) error {
+	return errors.New("Not implemented: printer.file")
+}
+
+func (p *printer) expr(expr ast.Expr) error {
+	return errors.New("Not implemented: printer.expr")
+}
+
+func (p *printer) stmt(node ast.Statement) error {
+	return errors.New("Not implemented: printer.stmt")
+}

printer/printer_test.go

@@ -0,0 +1,35 @@
+package printer
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/haya14busa/go-vimlparser"
+)
+
+func TestFprint_file(t *testing.T) {
+	src := `let _ = 1`
+	r := strings.NewReader(src)
+	node, err := vimlparser.ParseFile(r, "", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	buf := new(bytes.Buffer)
+	if err := Fprint(buf, node, nil); err == nil {
+		t.Error("want error")
+	}
+}
+
+func TestFprint_expr(t *testing.T) {
+	src := `1 + 2`
+	r := strings.NewReader(src)
+	node, err := vimlparser.ParseExpr(r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	buf := new(bytes.Buffer)
+	if err := Fprint(buf, node, nil); err == nil {
+		t.Error("want error")
+	}
+}