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struct.go
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struct.go
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package participle
import (
"fmt"
"reflect"
"strconv"
"strings"
"text/scanner"
"unicode/utf8"
"github.com/alecthomas/participle/v2/lexer"
)
// A structLexer lexes over the tags of struct fields while tracking the current field.
type structLexer struct {
s reflect.Type
field int
indexes [][]int
lexer *lexer.PeekingLexer
}
func lexStruct(s reflect.Type) (*structLexer, error) {
indexes, err := collectFieldIndexes(s)
if err != nil {
return nil, err
}
slex := &structLexer{
s: s,
indexes: indexes,
}
if len(slex.indexes) > 0 {
tag := fieldLexerTag(slex.Field().StructField)
slex.lexer, err = lexer.Upgrade(newTagLexer(s.Name(), tag))
if err != nil {
return nil, err
}
}
return slex, nil
}
// NumField returns the number of fields in the struct associated with this structLexer.
func (s *structLexer) NumField() int {
return len(s.indexes)
}
type structLexerField struct {
reflect.StructField
Index []int
}
// Field returns the field associated with the current token.
func (s *structLexer) Field() structLexerField {
return s.GetField(s.field)
}
func (s *structLexer) GetField(field int) structLexerField {
if field >= len(s.indexes) {
field = len(s.indexes) - 1
}
return structLexerField{
StructField: s.s.FieldByIndex(s.indexes[field]),
Index: s.indexes[field],
}
}
func (s *structLexer) Peek() (lexer.Token, error) {
field := s.field
lex := s.lexer
for {
token := lex.Peek()
if !token.EOF() {
token.Pos.Line = field + 1
return token, nil
}
field++
if field >= s.NumField() {
return lexer.EOFToken(token.Pos), nil
}
ft := s.GetField(field).StructField
tag := fieldLexerTag(ft)
var err error
lex, err = lexer.Upgrade(newTagLexer(ft.Name, tag))
if err != nil {
return token, err
}
}
}
func (s *structLexer) Next() (lexer.Token, error) {
token := s.lexer.Next()
if !token.EOF() {
token.Pos.Line = s.field + 1
return token, nil
}
if s.field+1 >= s.NumField() {
return lexer.EOFToken(token.Pos), nil
}
s.field++
ft := s.Field().StructField
tag := fieldLexerTag(ft)
var err error
s.lexer, err = lexer.Upgrade(newTagLexer(ft.Name, tag))
if err != nil {
return token, err
}
return s.Next()
}
func fieldLexerTag(field reflect.StructField) string {
if tag, ok := field.Tag.Lookup("parser"); ok {
return tag
}
return string(field.Tag)
}
// Recursively collect flattened indices for top-level fields and embedded fields.
func collectFieldIndexes(s reflect.Type) (out [][]int, err error) {
if s.Kind() != reflect.Struct {
return nil, fmt.Errorf("expected a struct but got %q", s)
}
defer decorate(&err, s.String)
for i := 0; i < s.NumField(); i++ {
f := s.Field(i)
switch {
case f.Anonymous: // nolint: gocritic
children, err := collectFieldIndexes(f.Type)
if err != nil {
return nil, err
}
for _, idx := range children {
out = append(out, append(f.Index, idx...))
}
case f.PkgPath != "":
continue
case fieldLexerTag(f) != "":
out = append(out, f.Index)
}
}
return
}
// tagLexer is a Lexer based on text/scanner.Scanner
type tagLexer struct {
scanner *scanner.Scanner
filename string
err error
}
func newTagLexer(filename string, tag string) *tagLexer {
s := &scanner.Scanner{}
s.Init(strings.NewReader(tag))
lexer := &tagLexer{
filename: filename,
scanner: s,
}
lexer.scanner.Error = func(s *scanner.Scanner, msg string) {
// This is to support single quoted strings. Hacky.
if !strings.HasSuffix(msg, "char literal") {
lexer.err = fmt.Errorf("%s: %s", lexer.scanner.Pos(), msg)
}
}
return lexer
}
func (t *tagLexer) Next() (lexer.Token, error) {
typ := t.scanner.Scan()
text := t.scanner.TokenText()
pos := lexer.Position(t.scanner.Position)
pos.Filename = t.filename
if t.err != nil {
return lexer.Token{}, t.err
}
return textScannerTransform(lexer.Token{
Type: lexer.TokenType(typ),
Value: text,
Pos: pos,
})
}
func textScannerTransform(token lexer.Token) (lexer.Token, error) {
// Unquote strings.
switch token.Type {
case scanner.Char:
// FIXME(alec): This is pretty hacky...we convert a single quoted char into a double
// quoted string in order to support single quoted strings.
token.Value = fmt.Sprintf("\"%s\"", token.Value[1:len(token.Value)-1])
fallthrough
case scanner.String:
s, err := strconv.Unquote(token.Value)
if err != nil {
return lexer.Token{}, Errorf(token.Pos, "%s: %q", err.Error(), token.Value)
}
token.Value = s
if token.Type == scanner.Char && utf8.RuneCountInString(s) > 1 {
token.Type = scanner.String
}
case scanner.RawString:
token.Value = token.Value[1 : len(token.Value)-1]
default:
}
return token, nil
}