grindlemire/go-tui code browser

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package highlight

import "unicode"

var goKeywords = wordsSet(`break default func interface select case defer go map struct
	chan else goto package switch const fallthrough if range type continue for import return var`)

var goLiterals = wordsSet(`true false nil iota`)

func lexGo(code string) []Token {
	rs := []rune(code)
	n := len(rs)
	var toks []Token
	var plain []rune
	flush := func() {
		if len(plain) > 0 {
			toks = append(toks, Token{KindPlain, string(plain)})
			plain = plain[:0]
		}
	}
	expectName := false // previous keyword was func/type
	for i := 0; i < n; {
		r := rs[i]
		switch {
		case r == '/' && i+1 < n && rs[i+1] == '/':
			flush()
			expectName = false
			j := i
			for j < n && rs[j] != '\n' {
				j++
			}
			toks = append(toks, Token{KindComment, string(rs[i:j])})
			i = j
		case r == '/' && i+1 < n && rs[i+1] == '*':
			flush()
			expectName = false
			j := i + 2
			for j < n && !(rs[j] == '*' && j+1 < n && rs[j+1] == '/') {
				j++
			}
			if j < n {
				j += 2
			} else {
				j = n
			}
			toks = append(toks, Token{KindComment, string(rs[i:j])})
			i = j
		case r == '`':
			flush()
			expectName = false
			j := i + 1
			for j < n && rs[j] != '`' {
				j++
			}
			if j < n {
				j++
			}
			toks = append(toks, Token{KindString, string(rs[i:j])})
			i = j
		case r == '"' || r == '\'':
			flush()
			expectName = false
			j := scanQuoted(rs, i)
			toks = append(toks, Token{KindString, string(rs[i:j])})
			i = j
		case isDigit(r) || (r == '.' && i+1 < n && isDigit(rs[i+1])):
			flush()
			expectName = false
			j := scanNumber(rs, i)
			toks = append(toks, Token{KindNumber, string(rs[i:j])})
			i = j
		case isIdentStart(r):
			flush()
			j := i + 1
			for j < n && isIdentPart(rs[j]) {
				j++
			}
			word := string(rs[i:j])
			kind := KindPlain
			switch {
			case goKeywords[word]:
				kind = KindKeyword
			case goLiterals[word]:
				kind = KindLiteral
			case expectName:
				kind = KindType
			case nextNonSpaceIs(rs, j, '('):
				kind = KindType
			case unicode.IsUpper(rs[i]):
				kind = KindType
			}
			expectName = (word == "func" || word == "type") && nextNonSpaceIsIdent(rs, j)
			toks = append(toks, Token{kind, word})
			i = j
		case isOperator(r):
			flush()
			expectName = false
			toks = append(toks, Token{KindOperator, string(r)})
			i++
		default:
			plain = append(plain, r)
			i++
		}
	}
	flush()
	return toks
}