mtfosbot/vendor/github.com/andybalholm/cascadia/parser.go

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2018-09-10 10:13:27 +00:00
// Package cascadia is an implementation of CSS selectors.
package cascadia
import (
"errors"
"fmt"
"regexp"
"strconv"
"strings"
"golang.org/x/net/html"
)
// a parser for CSS selectors
type parser struct {
s string // the source text
i int // the current position
}
// parseEscape parses a backslash escape.
func (p *parser) parseEscape() (result string, err error) {
if len(p.s) < p.i+2 || p.s[p.i] != '\\' {
return "", errors.New("invalid escape sequence")
}
start := p.i + 1
c := p.s[start]
switch {
case c == '\r' || c == '\n' || c == '\f':
return "", errors.New("escaped line ending outside string")
case hexDigit(c):
// unicode escape (hex)
var i int
for i = start; i < p.i+6 && i < len(p.s) && hexDigit(p.s[i]); i++ {
// empty
}
v, _ := strconv.ParseUint(p.s[start:i], 16, 21)
if len(p.s) > i {
switch p.s[i] {
case '\r':
i++
if len(p.s) > i && p.s[i] == '\n' {
i++
}
case ' ', '\t', '\n', '\f':
i++
}
}
p.i = i
return string(rune(v)), nil
}
// Return the literal character after the backslash.
result = p.s[start : start+1]
p.i += 2
return result, nil
}
func hexDigit(c byte) bool {
return '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F'
}
// nameStart returns whether c can be the first character of an identifier
// (not counting an initial hyphen, or an escape sequence).
func nameStart(c byte) bool {
return 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_' || c > 127
}
// nameChar returns whether c can be a character within an identifier
// (not counting an escape sequence).
func nameChar(c byte) bool {
return 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_' || c > 127 ||
c == '-' || '0' <= c && c <= '9'
}
// parseIdentifier parses an identifier.
func (p *parser) parseIdentifier() (result string, err error) {
startingDash := false
if len(p.s) > p.i && p.s[p.i] == '-' {
startingDash = true
p.i++
}
if len(p.s) <= p.i {
return "", errors.New("expected identifier, found EOF instead")
}
if c := p.s[p.i]; !(nameStart(c) || c == '\\') {
return "", fmt.Errorf("expected identifier, found %c instead", c)
}
result, err = p.parseName()
if startingDash && err == nil {
result = "-" + result
}
return
}
// parseName parses a name (which is like an identifier, but doesn't have
// extra restrictions on the first character).
func (p *parser) parseName() (result string, err error) {
i := p.i
loop:
for i < len(p.s) {
c := p.s[i]
switch {
case nameChar(c):
start := i
for i < len(p.s) && nameChar(p.s[i]) {
i++
}
result += p.s[start:i]
case c == '\\':
p.i = i
val, err := p.parseEscape()
if err != nil {
return "", err
}
i = p.i
result += val
default:
break loop
}
}
if result == "" {
return "", errors.New("expected name, found EOF instead")
}
p.i = i
return result, nil
}
// parseString parses a single- or double-quoted string.
func (p *parser) parseString() (result string, err error) {
i := p.i
if len(p.s) < i+2 {
return "", errors.New("expected string, found EOF instead")
}
quote := p.s[i]
i++
loop:
for i < len(p.s) {
switch p.s[i] {
case '\\':
if len(p.s) > i+1 {
switch c := p.s[i+1]; c {
case '\r':
if len(p.s) > i+2 && p.s[i+2] == '\n' {
i += 3
continue loop
}
fallthrough
case '\n', '\f':
i += 2
continue loop
}
}
p.i = i
val, err := p.parseEscape()
if err != nil {
return "", err
}
i = p.i
result += val
case quote:
break loop
case '\r', '\n', '\f':
return "", errors.New("unexpected end of line in string")
default:
start := i
for i < len(p.s) {
if c := p.s[i]; c == quote || c == '\\' || c == '\r' || c == '\n' || c == '\f' {
break
}
i++
}
result += p.s[start:i]
}
}
if i >= len(p.s) {
return "", errors.New("EOF in string")
}
// Consume the final quote.
i++
p.i = i
return result, nil
}
// parseRegex parses a regular expression; the end is defined by encountering an
// unmatched closing ')' or ']' which is not consumed
func (p *parser) parseRegex() (rx *regexp.Regexp, err error) {
i := p.i
if len(p.s) < i+2 {
return nil, errors.New("expected regular expression, found EOF instead")
}
// number of open parens or brackets;
// when it becomes negative, finished parsing regex
open := 0
loop:
for i < len(p.s) {
switch p.s[i] {
case '(', '[':
open++
case ')', ']':
open--
if open < 0 {
break loop
}
}
i++
}
if i >= len(p.s) {
return nil, errors.New("EOF in regular expression")
}
rx, err = regexp.Compile(p.s[p.i:i])
p.i = i
return rx, err
}
// skipWhitespace consumes whitespace characters and comments.
// It returns true if there was actually anything to skip.
func (p *parser) skipWhitespace() bool {
i := p.i
for i < len(p.s) {
switch p.s[i] {
case ' ', '\t', '\r', '\n', '\f':
i++
continue
case '/':
if strings.HasPrefix(p.s[i:], "/*") {
end := strings.Index(p.s[i+len("/*"):], "*/")
if end != -1 {
i += end + len("/**/")
continue
}
}
}
break
}
if i > p.i {
p.i = i
return true
}
return false
}
// consumeParenthesis consumes an opening parenthesis and any following
// whitespace. It returns true if there was actually a parenthesis to skip.
func (p *parser) consumeParenthesis() bool {
if p.i < len(p.s) && p.s[p.i] == '(' {
p.i++
p.skipWhitespace()
return true
}
return false
}
// consumeClosingParenthesis consumes a closing parenthesis and any preceding
// whitespace. It returns true if there was actually a parenthesis to skip.
func (p *parser) consumeClosingParenthesis() bool {
i := p.i
p.skipWhitespace()
if p.i < len(p.s) && p.s[p.i] == ')' {
p.i++
return true
}
p.i = i
return false
}
// parseTypeSelector parses a type selector (one that matches by tag name).
func (p *parser) parseTypeSelector() (result Selector, err error) {
tag, err := p.parseIdentifier()
if err != nil {
return nil, err
}
return typeSelector(tag), nil
}
// parseIDSelector parses a selector that matches by id attribute.
func (p *parser) parseIDSelector() (Selector, error) {
if p.i >= len(p.s) {
return nil, fmt.Errorf("expected id selector (#id), found EOF instead")
}
if p.s[p.i] != '#' {
return nil, fmt.Errorf("expected id selector (#id), found '%c' instead", p.s[p.i])
}
p.i++
id, err := p.parseName()
if err != nil {
return nil, err
}
return attributeEqualsSelector("id", id), nil
}
// parseClassSelector parses a selector that matches by class attribute.
func (p *parser) parseClassSelector() (Selector, error) {
if p.i >= len(p.s) {
return nil, fmt.Errorf("expected class selector (.class), found EOF instead")
}
if p.s[p.i] != '.' {
return nil, fmt.Errorf("expected class selector (.class), found '%c' instead", p.s[p.i])
}
p.i++
class, err := p.parseIdentifier()
if err != nil {
return nil, err
}
return attributeIncludesSelector("class", class), nil
}
// parseAttributeSelector parses a selector that matches by attribute value.
func (p *parser) parseAttributeSelector() (Selector, error) {
if p.i >= len(p.s) {
return nil, fmt.Errorf("expected attribute selector ([attribute]), found EOF instead")
}
if p.s[p.i] != '[' {
return nil, fmt.Errorf("expected attribute selector ([attribute]), found '%c' instead", p.s[p.i])
}
p.i++
p.skipWhitespace()
key, err := p.parseIdentifier()
if err != nil {
return nil, err
}
p.skipWhitespace()
if p.i >= len(p.s) {
return nil, errors.New("unexpected EOF in attribute selector")
}
if p.s[p.i] == ']' {
p.i++
return attributeExistsSelector(key), nil
}
if p.i+2 >= len(p.s) {
return nil, errors.New("unexpected EOF in attribute selector")
}
op := p.s[p.i : p.i+2]
if op[0] == '=' {
op = "="
} else if op[1] != '=' {
return nil, fmt.Errorf(`expected equality operator, found "%s" instead`, op)
}
p.i += len(op)
p.skipWhitespace()
if p.i >= len(p.s) {
return nil, errors.New("unexpected EOF in attribute selector")
}
var val string
var rx *regexp.Regexp
if op == "#=" {
rx, err = p.parseRegex()
} else {
switch p.s[p.i] {
case '\'', '"':
val, err = p.parseString()
default:
val, err = p.parseIdentifier()
}
}
if err != nil {
return nil, err
}
p.skipWhitespace()
if p.i >= len(p.s) {
return nil, errors.New("unexpected EOF in attribute selector")
}
if p.s[p.i] != ']' {
return nil, fmt.Errorf("expected ']', found '%c' instead", p.s[p.i])
}
p.i++
switch op {
case "=":
return attributeEqualsSelector(key, val), nil
case "!=":
return attributeNotEqualSelector(key, val), nil
case "~=":
return attributeIncludesSelector(key, val), nil
case "|=":
return attributeDashmatchSelector(key, val), nil
case "^=":
return attributePrefixSelector(key, val), nil
case "$=":
return attributeSuffixSelector(key, val), nil
case "*=":
return attributeSubstringSelector(key, val), nil
case "#=":
return attributeRegexSelector(key, rx), nil
}
return nil, fmt.Errorf("attribute operator %q is not supported", op)
}
var errExpectedParenthesis = errors.New("expected '(' but didn't find it")
var errExpectedClosingParenthesis = errors.New("expected ')' but didn't find it")
var errUnmatchedParenthesis = errors.New("unmatched '('")
// parsePseudoclassSelector parses a pseudoclass selector like :not(p).
func (p *parser) parsePseudoclassSelector() (Selector, error) {
if p.i >= len(p.s) {
return nil, fmt.Errorf("expected pseudoclass selector (:pseudoclass), found EOF instead")
}
if p.s[p.i] != ':' {
return nil, fmt.Errorf("expected attribute selector (:pseudoclass), found '%c' instead", p.s[p.i])
}
p.i++
name, err := p.parseIdentifier()
if err != nil {
return nil, err
}
name = toLowerASCII(name)
switch name {
case "not", "has", "haschild":
if !p.consumeParenthesis() {
return nil, errExpectedParenthesis
}
sel, parseErr := p.parseSelectorGroup()
if parseErr != nil {
return nil, parseErr
}
if !p.consumeClosingParenthesis() {
return nil, errExpectedClosingParenthesis
}
switch name {
case "not":
return negatedSelector(sel), nil
case "has":
return hasDescendantSelector(sel), nil
case "haschild":
return hasChildSelector(sel), nil
}
case "contains", "containsown":
if !p.consumeParenthesis() {
return nil, errExpectedParenthesis
}
if p.i == len(p.s) {
return nil, errUnmatchedParenthesis
}
var val string
switch p.s[p.i] {
case '\'', '"':
val, err = p.parseString()
default:
val, err = p.parseIdentifier()
}
if err != nil {
return nil, err
}
val = strings.ToLower(val)
p.skipWhitespace()
if p.i >= len(p.s) {
return nil, errors.New("unexpected EOF in pseudo selector")
}
if !p.consumeClosingParenthesis() {
return nil, errExpectedClosingParenthesis
}
switch name {
case "contains":
return textSubstrSelector(val), nil
case "containsown":
return ownTextSubstrSelector(val), nil
}
case "matches", "matchesown":
if !p.consumeParenthesis() {
return nil, errExpectedParenthesis
}
rx, err := p.parseRegex()
if err != nil {
return nil, err
}
if p.i >= len(p.s) {
return nil, errors.New("unexpected EOF in pseudo selector")
}
if !p.consumeClosingParenthesis() {
return nil, errExpectedClosingParenthesis
}
switch name {
case "matches":
return textRegexSelector(rx), nil
case "matchesown":
return ownTextRegexSelector(rx), nil
}
case "nth-child", "nth-last-child", "nth-of-type", "nth-last-of-type":
if !p.consumeParenthesis() {
return nil, errExpectedParenthesis
}
a, b, err := p.parseNth()
if err != nil {
return nil, err
}
if !p.consumeClosingParenthesis() {
return nil, errExpectedClosingParenthesis
}
if a == 0 {
switch name {
case "nth-child":
return simpleNthChildSelector(b, false), nil
case "nth-of-type":
return simpleNthChildSelector(b, true), nil
case "nth-last-child":
return simpleNthLastChildSelector(b, false), nil
case "nth-last-of-type":
return simpleNthLastChildSelector(b, true), nil
}
}
return nthChildSelector(a, b,
name == "nth-last-child" || name == "nth-last-of-type",
name == "nth-of-type" || name == "nth-last-of-type"),
nil
case "first-child":
return simpleNthChildSelector(1, false), nil
case "last-child":
return simpleNthLastChildSelector(1, false), nil
case "first-of-type":
return simpleNthChildSelector(1, true), nil
case "last-of-type":
return simpleNthLastChildSelector(1, true), nil
case "only-child":
return onlyChildSelector(false), nil
case "only-of-type":
return onlyChildSelector(true), nil
case "input":
return inputSelector, nil
case "empty":
return emptyElementSelector, nil
case "root":
return rootSelector, nil
}
return nil, fmt.Errorf("unknown pseudoclass :%s", name)
}
// parseInteger parses a decimal integer.
func (p *parser) parseInteger() (int, error) {
i := p.i
start := i
for i < len(p.s) && '0' <= p.s[i] && p.s[i] <= '9' {
i++
}
if i == start {
return 0, errors.New("expected integer, but didn't find it")
}
p.i = i
val, err := strconv.Atoi(p.s[start:i])
if err != nil {
return 0, err
}
return val, nil
}
// parseNth parses the argument for :nth-child (normally of the form an+b).
func (p *parser) parseNth() (a, b int, err error) {
// initial state
if p.i >= len(p.s) {
goto eof
}
switch p.s[p.i] {
case '-':
p.i++
goto negativeA
case '+':
p.i++
goto positiveA
case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
goto positiveA
case 'n', 'N':
a = 1
p.i++
goto readN
case 'o', 'O', 'e', 'E':
id, nameErr := p.parseName()
if nameErr != nil {
return 0, 0, nameErr
}
id = toLowerASCII(id)
if id == "odd" {
return 2, 1, nil
}
if id == "even" {
return 2, 0, nil
}
return 0, 0, fmt.Errorf("expected 'odd' or 'even', but found '%s' instead", id)
default:
goto invalid
}
positiveA:
if p.i >= len(p.s) {
goto eof
}
switch p.s[p.i] {
case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
a, err = p.parseInteger()
if err != nil {
return 0, 0, err
}
goto readA
case 'n', 'N':
a = 1
p.i++
goto readN
default:
goto invalid
}
negativeA:
if p.i >= len(p.s) {
goto eof
}
switch p.s[p.i] {
case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
a, err = p.parseInteger()
if err != nil {
return 0, 0, err
}
a = -a
goto readA
case 'n', 'N':
a = -1
p.i++
goto readN
default:
goto invalid
}
readA:
if p.i >= len(p.s) {
goto eof
}
switch p.s[p.i] {
case 'n', 'N':
p.i++
goto readN
default:
// The number we read as a is actually b.
return 0, a, nil
}
readN:
p.skipWhitespace()
if p.i >= len(p.s) {
goto eof
}
switch p.s[p.i] {
case '+':
p.i++
p.skipWhitespace()
b, err = p.parseInteger()
if err != nil {
return 0, 0, err
}
return a, b, nil
case '-':
p.i++
p.skipWhitespace()
b, err = p.parseInteger()
if err != nil {
return 0, 0, err
}
return a, -b, nil
default:
return a, 0, nil
}
eof:
return 0, 0, errors.New("unexpected EOF while attempting to parse expression of form an+b")
invalid:
return 0, 0, errors.New("unexpected character while attempting to parse expression of form an+b")
}
// parseSimpleSelectorSequence parses a selector sequence that applies to
// a single element.
func (p *parser) parseSimpleSelectorSequence() (Selector, error) {
var result Selector
if p.i >= len(p.s) {
return nil, errors.New("expected selector, found EOF instead")
}
switch p.s[p.i] {
case '*':
// It's the universal selector. Just skip over it, since it doesn't affect the meaning.
p.i++
case '#', '.', '[', ':':
// There's no type selector. Wait to process the other till the main loop.
default:
r, err := p.parseTypeSelector()
if err != nil {
return nil, err
}
result = r
}
loop:
for p.i < len(p.s) {
var ns Selector
var err error
switch p.s[p.i] {
case '#':
ns, err = p.parseIDSelector()
case '.':
ns, err = p.parseClassSelector()
case '[':
ns, err = p.parseAttributeSelector()
case ':':
ns, err = p.parsePseudoclassSelector()
default:
break loop
}
if err != nil {
return nil, err
}
if result == nil {
result = ns
} else {
result = intersectionSelector(result, ns)
}
}
if result == nil {
result = func(n *html.Node) bool {
return n.Type == html.ElementNode
}
}
return result, nil
}
// parseSelector parses a selector that may include combinators.
func (p *parser) parseSelector() (result Selector, err error) {
p.skipWhitespace()
result, err = p.parseSimpleSelectorSequence()
if err != nil {
return
}
for {
var combinator byte
if p.skipWhitespace() {
combinator = ' '
}
if p.i >= len(p.s) {
return
}
switch p.s[p.i] {
case '+', '>', '~':
combinator = p.s[p.i]
p.i++
p.skipWhitespace()
case ',', ')':
// These characters can't begin a selector, but they can legally occur after one.
return
}
if combinator == 0 {
return
}
c, err := p.parseSimpleSelectorSequence()
if err != nil {
return nil, err
}
switch combinator {
case ' ':
result = descendantSelector(result, c)
case '>':
result = childSelector(result, c)
case '+':
result = siblingSelector(result, c, true)
case '~':
result = siblingSelector(result, c, false)
}
}
panic("unreachable")
}
// parseSelectorGroup parses a group of selectors, separated by commas.
func (p *parser) parseSelectorGroup() (result Selector, err error) {
result, err = p.parseSelector()
if err != nil {
return
}
for p.i < len(p.s) {
if p.s[p.i] != ',' {
return result, nil
}
p.i++
c, err := p.parseSelector()
if err != nil {
return nil, err
}
result = unionSelector(result, c)
}
return
}