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inline.go
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inline.go
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// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package markdown
import (
"strings"
"unicode/utf8"
)
// An Inline is an inline Markdown element, one of
// [Plain], [Escaped], [Code], [Strong], [Emph], [Del],
// [Link], [AutoLink], [Image],
// [SoftBreak], [HardBreak],
// [HTMLTag],
// [Emoji], and [Task].
type Inline interface {
Inline()
printHTML(*printer)
printText(*printer)
printMarkdown(*printer)
}
// An Inlines is an [Inline] that represents a concatenation of Inlines.
type Inlines []Inline
func (Inlines) Inline() {}
func (x Inlines) printText(p *printer) {
for _, inl := range x {
inl.printText(p)
}
}
func (x Inlines) printHTML(p *printer) {
for _, inl := range x {
inl.printHTML(p)
}
}
func (x Inlines) printMarkdown(p *printer) {
for _, inl := range x {
inl.printMarkdown(p)
}
}
// A Plain is an [Inline] that represents [plain textual content].
//
// [textual content]: https://spec.commonmark.org/0.31.2/#textual-content
type Plain struct {
Text string
}
func (*Plain) Inline() {}
func (x *Plain) printText(p *printer) { p.text(x.Text) }
func (x *Plain) printHTML(p *printer) { p.text(x.Text) }
func (x *Plain) printMarkdown(p *printer) {
// TODO: This is wrong if Plain contains characters that should be escaped.
// Today that doesn't happen for our own parses, but constructed syntax trees
// might contain them.
// Deciding exactly what to escape is (or probably should be) somewhat context dependent.
for i, line := range strings.Split(x.Text, "\n") {
if i > 0 {
p.nl()
}
p.WriteString(line)
p.noTrim()
}
}
// An Escaped is an [Inline] that represents a [backslash escaped symbol].
//
// [backslash escaped symbol]: https://spec.commonmark.org/0.31.2/#backslash-escapes
type Escaped struct {
Plain // single character text (omitting the escaping backslash)
}
func (x *Escaped) printMarkdown(p *printer) {
p.md(`\`)
p.md(x.Text)
}
// A Code is an [Inline] that represents a [code span].
//
// [code span]: https://spec.commonmark.org/0.31.2/#code-spans
type Code struct {
Text string
}
func (*Code) Inline() {}
func (x *Code) printText(p *printer) { p.text(x.Text) }
func (x *Code) printHTML(p *printer) {
p.html(`<code>`)
p.text(x.Text)
p.html(`</code>`)
}
var ticks = "````````````````````````````````````````````````````````````````" // 64 ticks
func (x *Code) printMarkdown(p *printer) {
// Use the fewest backticks we can, and add spaces as needed.
n := maxRun(x.Text, '`') + 1
printTicks(p, n)
// Note: len(x.Text)==0 is not possible to express in Markdown,
// but if someone makes a buggy Code, we print it as ` ` (a code-formatted space),
// since the only other choice would be to not print any code text at all, which is worse.
space := len(x.Text) == 0 || x.Text[0] == '`' || x.Text[len(x.Text)-1] == '`'
if space {
p.WriteByte(' ')
}
p.WriteString(x.Text)
if space {
p.WriteByte(' ')
}
printTicks(p, n)
}
// maxRun returns the length of the longest run of b bytes in s.
func maxRun(s string, b byte) int {
m := 0
n := 0
for i := range len(s) {
if s[i] == b {
n++
m = max(m, n)
} else {
n = 0
}
}
return m
}
// printTicks prints n backticks to p.
func printTicks(p *printer, n int) {
for n > len(ticks) {
p.md(ticks)
n -= len(ticks)
}
p.md(ticks[:n])
}
// A Strong is an [Inline] that represents [strong emphasis] (bold text).
//
// [strong emphasis]: https://spec.commonmark.org/0.31.2/#emphasis-and-strong-emphasis
type Strong struct {
Marker string
Inner Inlines
}
func (*Strong) Inline() {}
func (x *Strong) printText(p *printer) { x.Inner.printText(p) }
func (x *Strong) printHTML(p *printer) {
p.html("<strong>")
x.Inner.printHTML(p)
p.html("</strong>")
}
func (x *Strong) printMarkdown(p *printer) {
p.md(x.Marker)
x.Inner.printMarkdown(p)
p.md(x.Marker)
}
// An Emph is an [Inline] representing [emphasis] (italic text).
//
// [emphasis]: https://spec.commonmark.org/0.31.2/#emphasis-and-strong-emphasis
type Emph struct {
Marker string
Inner Inlines
}
func (*Emph) Inline() {}
func (x *Emph) printText(p *printer) { x.Inner.printText(p) }
func (x *Emph) printHTML(p *printer) {
p.html("<em>")
x.Inner.printHTML(p)
p.html("</em>")
}
func (x *Emph) printMarkdown(p *printer) {
p.md(x.Marker)
x.Inner.printMarkdown(p)
p.md(x.Marker)
}
// A Deleted is an [Inline] that represents [deleted (strikethrough) text],
// a GitHub-flavored Markdown extension.
//
// [deleted (strikethrough) text]: https://github.github.com/gfm/#strikethrough-extension-
type Del struct {
Marker string
Inner Inlines
}
func (*Del) Inline() {}
func (x *Del) printText(p *printer) { x.Inner.printText(p) }
func (x *Del) printHTML(p *printer) {
p.html("<del>")
x.Inner.printHTML(p)
p.html("</del>")
}
func (x *Del) printMarkdown(p *printer) {
p.WriteString(x.Marker)
x.Inner.printMarkdown(p)
p.WriteString(x.Marker)
}
// An Emoji is an [Inline] that represents an emoji, like :smiley:,
// an apparently undocumented but widely used GitHub Markdown extension.
type Emoji struct {
Name string // emoji :name:, including colons
Text string // Unicode for emoji sequence
}
func (*Emoji) Inline() {}
func (x *Emoji) printText(p *printer) { p.text(x.Text) }
func (x *Emoji) printHTML(p *printer) { p.text(x.Text) }
func (x *Emoji) printMarkdown(p *printer) { p.text(x.Text) }
// Parsing Inlines
//
// The parser walks over the text looking for opening special characters such as * or [
// and pushes them onto a parse stack. This same scan also looks for and pushes
// special leaf inlines such as escaped symbols, HTML entities, code spans, and line breaks.
// Text between special cases is also pushed, as plain text (type Plain).
// When the parser sees a closing special character such as * or ], it tries to match
// that closing special against a corresponding opening special. If it can, the stack
// content between the opening and the closing becomes the inner inline of a new
// node (for example, an Emph or a Link), and that new node is pushed on the stack
// in place of the opening and the inner content.
//
// The matching proceeds in two phases: brackets first, then emphasis
// (* and _, as well as the extensions ~ ' and "). This is because links and images
// take priority over emphasis: "this *nice [link*](/emph)" contains a link
// but no emphasis: the * outside the link brackets cannot match the * inside.
//
// Another subtlety is that link text can contain images:
//
// [link ![foo](img.jpg)](/) ⇒
// <a href="/">link <img src="img.jpg" alt="foo" /></a>
//
// But link text cannot contain links:
//
// [link [foo](img.jpg)](/) ⇒
// [link <a href="img.jpg">foo</a>](/)
//
// (note the missing !).
//
// Image text can contain links, images, and emphasized text,
// but all that turns into plain text when formatted in the alt tag:
//
// ![link ![foo](img.jpg) [bar](/)](/) ⇒
// <img src="/" alt="link foo bar" />
//
// The prohibition on links containing links applies even to
// links containing images containing links:
//
// [outer ![link ![foo](img.jpg) [bar](/)](/)](/out) ⇒
// [outer <img src="/" alt="link foo bar" />](/out)
//
// [outer ![link ![foo](img.jpg) ![bar](/)](/)](/out) ⇒
// <a href="/out">outer <img src="/" alt="link foo bar" /></a>
//
// Yet another subtlety is that straightforward implementation of parts of this
// would be accidentally quadratic (see tumblr.com/accidentallyquadratic),
// leading to performance problems and potential denial of service attacks.
// We must take care to avoid quadratic behavior.
// An inlineParser parses s[start:] into an Inline, returning the Inline
// and the string index where the inline ends
// (that is, the Inline represents s[start:end]).
// If it cannot parse s[start:], it returns ok=false.
// The caller has usually checked that s[start:] is likely to be appropriate
// for this parser.
type inlineParser func(p *parser, s string, start int) (x Inline, end int, ok bool)
// emit emits p.s[p.emitted:i] as plain text and then sets p.emitted = i.
// (p.emitted keeps track of the place in the current line has has been emitted
// onto the stack in some form already.)
func (p *parser) emit(i int) {
if p.emitted < i {
p.list = append(p.list, &Plain{p.s[p.emitted:i]})
p.emitted = i
}
}
// skip sets p.emitted = i.
func (p *parser) skip(i int) {
p.emitted = i
}
// An openPlain is an [Inline] that represents an opening marker
// [ or ![ that has not yet been matched to a closing marker.
// It only exists on the parse stack, not in the final returned Markdown.
type openPlain struct {
Plain
i int // position in input where bracket is
}
// An emphPlain is an [Inline] that represents an opening emphasis marker
// such as * or _ that has not yet been matched to a closing marker.
// It only exists on the parse stack, not in the final returned Markdown.
type emphPlain struct {
Plain
canOpen bool // marker can open emphasis
canClose bool // marker can close emphasis
i int // position in output where emph is
n int // length of original span
}
// inline parses s into an Inlines.
//
// In terms of the “Parsing Inlines” comment above, inline handles the
// scanning of the string into a parse stack and the construction of links
// and images; the emphasis processing is delegated to [parser.emph].
func (p *parser) inline(s string) Inlines {
p.lineInfo = lineInfo{}
s = trimSpaceTab(s)
p.s = s
p.list = nil
p.emitted = 0
// Scan text looking for inlines.
// Leaf inlines are converted immediately.
// Potential link and image openings are pushed onto a stack while we await completion.
// Emphasis is applied by p.emph once we identify the link and image boundaries.
var opens []int // indexes of open ![ and [ openPlains in p.list
var ignoreLinkBefore int // ignore link openings before this stack offset, to avoid links inside links
backticksReset := false // for lazy initialization of p.backticks
for off := 0; off < len(s); {
// Determine the parser based on leading character.
var parser inlineParser
switch s[off] {
case '\\':
parser = parseEscape
case '`':
if !backticksReset {
p.backticks.reset()
backticksReset = true
}
parser = p.backticks.parseCodeSpan
case '<':
parser = parseAutoLinkOrHTML
case '[':
parser = parseLinkOpen
case '!':
parser = parseImageOpen
case '_', '*':
parser = parseEmph
case '.':
if p.SmartDot {
parser = parseDot
}
case '-':
if p.SmartDash {
parser = parseDash
}
case '"', '\'':
if p.SmartQuote {
parser = parseEmph
}
case '~':
if p.Strikethrough {
parser = parseEmph
}
case '\n': // TODO what about eof
parser = parseBreak
case '&':
parser = parseHTMLEntity
case ':':
if p.Emoji {
parser = parseEmoji
}
}
// If there is a parser, run it.
if parser != nil {
if x, end, ok := parser(p, s, off); ok {
// Emit plain text to list up through start.
p.emit(off)
// Add x to list, recording locations of openPlain entries.
if _, ok := x.(*openPlain); ok {
opens = append(opens, len(p.list))
}
p.list = append(p.list, x)
// Skip over x's extent in future plain text emits.
p.skip(end)
off = end
// Keep parsing.
continue
}
}
// If there's a closing bracket, match it to an opening bracket.
if s[off] == ']' && len(opens) > 0 {
// Pop most recent opening index from opens.
oi := opens[len(opens)-1]
opens = opens[:len(opens)-1]
// Match to the openPlain in the list.
// An image is valid anywhere; a link is only valid if it starts
// after ignoreLinkBefore, to avoid links containing links.
open := p.list[oi].(*openPlain)
if open.i >= ignoreLinkBefore || open.Text[0] == '!' {
if x, end, ok := parseLinkClose(p, s, off, open); ok {
p.emit(off)
x.Inner = p.emph(nil, p.list[oi+1:])
if open.Text[0] == '!' {
// parseLinkClose always returns a *Link.
// By design, Link and Image are the same underlying struct,
// so we can convert to *Image here.
p.list[oi] = (*Image)(x)
} else {
p.list[oi] = x
}
p.list = p.list[:oi+1]
p.skip(end)
off = end
if open.Text[0] == '[' {
// No links around links.
ignoreLinkBefore = open.i
}
// Goldmark and the Dingus re-escape invalid-looking percents as %25,
// but the spec does not seem to require this behavior.
url := x.URL
for i := 0; i < len(url); i++ {
if url[i] == '%' && (i+2 >= len(url) || !isHexDigit(url[i+1]) || !isHexDigit(url[i+2])) {
p.corner = true
break
}
}
continue
}
}
}
// Unspecial character; advance to next character.
off++
}
// Emit remainder of string.
p.emit(len(s))
// Apply emphasis to stack (topmost Inlines we will return).
p.list = p.emph(p.list[:0], p.list)
// Merge adjacent Plain elements in the list, so that for example
// abc*def is Plain{abc*def} and not Plain{abc}Plain{*}Plain{def}.
// (The * was tracked separately because it might have started emphasis.)
p.list = p.mergePlain(p.list)
// Apply GitHub autolinks to result, if extension is enabled.
p.list = autoLinkText(p, p.list)
return p.list
}
// emph applies emphasis in a run of inlines that has already had links and images converted.
// The links and images themselves contains inlines that have already had emph run.
// This function only has to process the inlines in src itself.
// It appends the new sequence of inlines to dst.
// dst and src may point at the same underlying array, provided &dst[0] == &src[0],
// in which case appending to dst will overwrite src, but that's okay because the
// number of elements in src only decreases or stays the same as it gets converted.
// emph may edit the values in src.
//
// This algorithm is fairly complicated and also fairly difficult to disentangle.
// TODO: Try harder.
func (ps *parser) emph(dst, src []Inline) []Inline {
// For each emphasis character, we maintain a stack of the
// possible openings we have seen, as *emphPlain nodes,
// for matching against closings using the same character.
// (The conversion to *emphPlain happened during p.inline,
// when it called parseEmph.)
const (
stackStrike = 0 // also 1
stackSingleQuote = 2
stackDoubleQuote = 3
stackStar = 4 // also 5..9
stackUnder = 10 // also 11..15
stackTotal = 16
)
var stack [stackTotal][]*emphPlain
Src:
for i := 0; i < len(src); i++ {
// Look for emphPlains; append the rest to dst.
inl := src[i]
p, ok := inl.(*emphPlain)
if !ok {
if open, ok := inl.(*openPlain); ok {
// Convert unused link/image open marker (*openPlain) to plain text (*Plain).
inl = &open.Plain
}
dst = append(dst, inl)
continue
}
if p.canClose {
// If this is a potential closing emphasis, try to match to earlier opening.
// A closing ** might match against an earlier ** but also might match
// against two separate *, as in "*hello *world**",
// or might match against only one *, as in *hello world**,
// which ends in a literal *.
// When a repeated character closes only a single character,
// the handling of * (or _ or ~) removes one character
// from p.Text and does goto PText to process p.Text again.
PText:
// Easy special cases.
switch p.Text[0] {
case '"':
stk := stack[stackDoubleQuote]
if len(stk) == 0 {
goto EmitPlain
}
stk, start := stk[:len(stk)-1], stk[len(stk)-1]
stack[stackDoubleQuote] = stk
// Rewrite "hello" into “hello”.
dst[start.i].(*emphPlain).Text = "“"
p.Text = "”"
dst = append(dst, &p.Plain)
continue Src
case '\'':
stk := stack[stackSingleQuote]
if len(stk) == 0 {
goto EmitPlain
}
stk, start := stk[:len(stk)-1], stk[len(stk)-1]
stack[stackSingleQuote] = stk
// Rewrite 'hello' into ‘hello’.
dst[start.i].(*emphPlain).Text = "‘"
p.Text = "’"
dst = append(dst, &p.Plain)
continue Src
}
// General case: emphasis containing other inlines.
var start *emphPlain
switch p.Text[0] {
case '~':
si := stackStrike + len(p.Text) - 1
stk := stack[si]
if len(stk) == 0 {
goto EmitPlain
}
start = stk[len(stk)-1]
case '*', '_':
// Complicated Markdown rule:
// “If one of the delimiters can both open and close emphasis, then the sum of the lengths
// of the delimiter runs containing the opening and closing delimiters must not
// be a multiple of 3 unless both lengths are multiples of 3.”
// (https://spec.commonmark.org/0.31.2/#emphasis-and-strong-emphasis, rule 9)
allow := func(p, start *emphPlain) bool {
return (!p.canOpen && !start.canClose) || // neither can do both
(p.n+start.n)%3 != 0 || // total not a multiple of 3
p.n%3 == 0 // both are multiples of 3 (checking one implies the other)
}
// Consider the six possible stacks (3 n%3 values × 2 canClose bool values)
// and take the acceptable one that appears latest in dst.
// We could have one stack for each of * and _ and then walk down it to
// find an acceptable value, but if we do that, there is the possibility of
// a malicious input causing us to walk arbitrarily far down the stack
// only to find nothing, again and again, triggering quadratic behavior.
si := stackStar
if p.Text[0] == '_' {
si = stackUnder
}
for i := si; i < si+6; i++ {
if len(stack[i]) == 0 {
continue
}
maybe := stack[i][len(stack[i])-1]
if allow(p, maybe) && (start == nil || maybe.i > start.i) {
start = maybe
}
}
if start == nil {
goto EmitPlain
}
}
// Match open and close. If both sides have >= 2 delimiters,
// we chop 2 off each; otherwise we chop 1.
var d int
if len(p.Text) >= 2 && len(start.Text) >= 2 {
// strong
d = 2
} else {
// emph
d = 1
}
del := p.Text[0] == '~'
// Create emphasis node containing stack between open and close.
x := &Emph{Marker: p.Text[:d], Inner: append([]Inline(nil), ps.mergePlain(dst[start.i+1:])...)}
// Remove used delimiters from start; if start is empty, remove it from dst.
// Otherwise leave it at the top of dst (we will push x onto dst below).
start.Text = start.Text[:len(start.Text)-d]
if start.Text == "" {
dst = dst[:start.i]
} else {
dst = dst[:start.i+1]
}
// Now that we've popped all the inner content from dst (and possibly start as well),
// pop everything is gone from the stacks too.
for i := range stack {
if len(stack[i]) > 0 {
stk := stack[i]
for len(stk) > 0 && stk[len(stk)-1].i >= len(dst) {
stk = stk[:len(stk)-1]
}
stack[i] = stk
}
}
// Push x (of correct type) onto dst.
// By design, Del, Strong, and Emph are all the same
// underlying struct, so we create an Emph above and
// convert it to the right type here.
if del {
dst = append(dst, (*Del)(x))
} else if d == 2 {
dst = append(dst, (*Strong)(x))
} else {
dst = append(dst, x)
}
// Remove used delimiters from p and go around again.
p.Text = p.Text[d:]
if p.Text == "" {
continue Src
}
goto PText
}
EmitPlain:
if p.canOpen {
p.i = len(dst)
dst = append(dst, p)
si := -1
switch p.Text[0] {
case '~':
si = stackStrike + len(p.Text) - 1
case '\'':
si = stackSingleQuote
case '"':
si = stackDoubleQuote
case '*', '_':
si = stackStar
if p.Text[0] == '_' {
si = stackUnder
}
if p.canClose {
si += 3
}
si += p.n % 3
}
stk := &stack[si]
*stk = append(*stk, p)
} else {
dst = append(dst, &p.Plain)
}
// Rewrite unmatched quotes to right quotes.
// Do this after the p.canOpen switch above,
// which looks for the original ASCII quotes.
if p.Text == "'" {
p.Text = "’"
}
if p.Text == "\"" {
if p.canClose {
p.Text = "”"
} else {
p.Text = "“"
}
}
}
return ps.mergePlain(dst)
}
// parseEscape is an [inlineParser] for an [Escaped] or [HardBreak].
func parseEscape(p *parser, s string, start int) (x Inline, end int, ok bool) {
if start+1 < len(s) {
c := s[start+1]
end = start + 2
if isPunct(c) {
return &Escaped{Plain{s[start+1 : end]}}, end, true
}
if c == '\n' { // TODO what about eof
if start > 0 && s[start-1] == '\\' {
p.corner = true // goldmark mishandles \\\ newline
}
return &HardBreak{}, end, true
}
}
return nil, 0, false
}
// parseAutoLinkOrHTML is an [inlineParser] for a Markdown autolink (not GitHub autolink)
// or an HTML tag. The caller has checked that s[start] == '<'.
func parseAutoLinkOrHTML(p *parser, s string, start int) (x Inline, end int, ok bool) {
if x, end, ok = parseAutoLinkURI(s, start); ok {
return
}
if x, end, ok = parseAutoLinkEmail(s, start); ok {
return
}
if x, end, ok = parseHTMLTag(p, s, start); ok {
return
}
return
}
// parseDot is an [inlineParser] for a “smart” ellipsis when the
// SmartDot extension is enabled. It rewrites "..." into "…".
func parseDot(p *parser, s string, i int) (x Inline, end int, ok bool) {
if i+2 < len(s) && s[i+1] == '.' && s[i+2] == '.' {
return &Plain{"…"}, i + 3, true
}
return
}
// parseDash is an [inlineParser] for a “smart” endash and emdash
// when the SmartDash extension is enabled.
// It rewrites -- into – and --- into —.
func parseDash(p *parser, s string, i int) (x Inline, end int, ok bool) {
if i+1 >= len(s) || s[i+1] != '-' {
return
}
n := 2
for i+n < len(s) && s[i+n] == '-' {
n++
}
// Obviously -- is – and --- is —,
// but what about ----? -----? ------?
// We blindly follow cmark-gfm's rules.
em, en := 0, 0
switch {
case n%3 == 0:
em = n / 3
case n%2 == 0:
en = n / 2
case n%3 == 2:
em = (n - 2) / 3
en = 1
case n%3 == 1:
em = (n - 4) / 3
en = 2
}
return &Plain{strings.Repeat("—", em) + strings.Repeat("–", en)}, i + n, true
}
// parseEmoji is an [inlineParser] for an [Emoji], which is
// a GitHub-style emoji reference like ":smiley:".
// The caller has checked that s[start] == ':'.
func parseEmoji(p *parser, s string, start int) (x Inline, end int, ok bool) {
for end := start + 1; ; end++ {
if end >= len(s) || end-start > 2+maxEmojiLen {
break
}
if s[end] == ':' {
name := s[start+1 : end]
end++
if utf, ok := emoji[name]; ok {
return &Emoji{s[start:end], utf}, end, true
}
break
}
}
return nil, 0, false
}
// maxBackticks is the maximum number of backticks allowed for an inline code span.
// To avoid super-linear (not quite quadratic) behavior, we need to track the last position
// where a run of exactly N backticks was seen, for each possible N, rather than scan
// backward to find them. This means we must place some limit on N (or use a map).
// cmark-gfm imposes a limit of 80, which seems good enough.
// (If your backticks don't fit on a punch card, you can't use them!)
const maxBackticks = 80
// A backtickParser holds the state for parseCodeSpan looking for backticks.
type backtickParser struct {
last [maxBackticks]int // last[n] = start offset where final run of n backticks was seen
scanned bool // whether we've scanned the string already
}
// reset resets the backtickParser for use with a new string.
func (b *backtickParser) reset() {
*b = backtickParser{}
}
// parseCodeSpan is (as b.parseCodeSpan) an [inlineParser] for a [Code],
// which is an n-backtick-delimited code span for some n.
// The naive implementation of backtick scanning would take O(n√n) time on an input like
//
// ` `` ``` ```` ````` `````` ``````` ````````
//
// It's not quite quadratic, because you can only make O(√n) scans of suffixes of a string of
// length n, but those will still do O(n√n) character comparisons because there are so many
// more backtick runs toward the start of the string than toward the end.
//
// Successful scans are always fine: they consume all the text they scanned.
// To avoid O(n√n) behavior, an unsuccessful scan records the
// To avoid this, during an unsuccessful scan for any length, we record the
// last location of every run of n backticks for all n, in an array indexed by n-1.
// Then, the next time we do a scan in the string, we can tell whether it will
// be successful by checking whether start < last[n-1]. If not, there's no
// terminator out there and we can avoid scanning.
// Otherwise, there's a guaranteed terminator, so a successful scan
// pays for itself by shortening s by the scan amount.
func (b *backtickParser) parseCodeSpan(p *parser, s string, start int) (x Inline, end int, ok bool) {
// Count leading backticks. Need to find that many again.
n := 1
for start+n < len(s) && s[start+n] == '`' {
n++
}
// If we've already scanned the whole string (for a different count),
// we can skip a failed scan by checking whether we saw this count.
// To enable this optimization, following cmark-gfm, we declare by fiat
// that more than maxBackticks backquotes is too many.
if n > len(b.last) || b.scanned && b.last[n-1] < start+n {
goto NoMatch
}
for end = start + n; end < len(s); {
if s[end] != '`' {
end++
continue
}
estart := end
for end < len(s) && s[end] == '`' {
end++
}
m := end - estart
if !b.scanned && m < len(b.last) {
b.last[m-1] = estart
}
if m == n {
// Match.
// Line endings are converted to single spaces.
text := s[start+n : estart]
text = strings.ReplaceAll(text, "\n", " ")
// If enclosed text starts and ends with a space and is not all spaces,
// one space is removed from start and end, to allow `` ` `` to quote a single backquote.
if len(text) >= 2 && text[0] == ' ' && text[len(text)-1] == ' ' && trimSpace(text) != "" {
text = text[1 : len(text)-1]
}
return &Code{text}, end, true
}
}
b.scanned = true
NoMatch:
// No match, so none of these backticks count: skip them all.
// For example ``x` is not a single backtick followed by a code span.
// Returning nil, 0, false would advance to the second backtick and try again.
end = start + n
return &Plain{s[start:end]}, end, true
}
// parseEmph is an [inlineParser] for an emphasis open or close (* _ ~)
// represented as an [emphPlain].
func parseEmph(p *parser, s string, start int) (x Inline, end int, ok bool) {
c := s[start]
end = start + 1
if c == '*' || c == '~' || c == '_' {
for end < len(s) && s[end] == c {
end++
}
}
if c == '~' && end-start != 2 {
// Goldmark does not accept ~text~
// and incorrectly accepts ~~~text~~~.
// Only ~~ is correct.
p.corner = true
}
if c == '~' && end-start > 2 {
// Skip over all the ~ so that we don't see
// the last two as a marker later and also to
// avoid quadratic scans over the ~s.
return &Plain{s[start:end]}, end, true
}
// Pick up the runes before and after the end.
before, after := ' ', ' '
if start > 0 {
before, _ = utf8.DecodeLastRuneInString(s[:start])
}
if end < len(s) {
after, _ = utf8.DecodeRuneInString(s[end:])
}
// See https://spec.commonmark.org/0.31.2/#emphasis-and-strong-emphasis.
//
// “A left-flanking delimiter run is a delimiter run that is
// (1) not followed by Unicode whitespace, and either
// (2a) not followed by a Unicode punctuation character, or
// (2b) followed by a Unicode punctuation character
// and preceded by Unicode whitespace or a Unicode punctuation character.
// For purposes of this definition, the beginning and the end
// of the line count as Unicode whitespace.”
leftFlank := !isUnicodeSpace(after) &&
(!isUnicodePunct(after) || isUnicodeSpace(before) || isUnicodePunct(before))
// “A right-flanking delimiter run is a delimiter run that is
// (1) not preceded by Unicode whitespace, and either
// (2a) not preceded by a Unicode punctuation character, or
// (2b) preceded by a Unicode punctuation character
// and followed by Unicode whitespace or a Unicode punctuation character.
// For purposes of this definition, the beginning and the end
// of the line count as Unicode whitespace.”
rightFlank := !isUnicodeSpace(before) &&
(!isUnicodePunct(before) || isUnicodeSpace(after) || isUnicodePunct(after))
var canOpen, canClose bool
switch c {
case '\'', '"':
canOpen = leftFlank && !rightFlank && before != ']' && before != ')'
canClose = rightFlank
case '*', '~':
// “A single * character can open emphasis iff
// it is part of a left-flanking delimiter run.”
// “A double ** can open strong emphasis iff
// it is part of a left-flanking delimiter run.”
canOpen = leftFlank
// “A single * character can close emphasis iff
// it is part of a right-flanking delimiter run.”
// “A double ** can close strong emphasis iff
// it is part of a right-flanking delimiter run.”
canClose = rightFlank
case '_':
// “A single _ character can open emphasis iff
// it is part of a left-flanking delimiter run and either
// (a) not part of a right-flanking delimiter run or
// (b) part of a right-flanking delimiter run preceded by a Unicode punctuation character.”
// “A double __ can open strong emphasis iff
// it is part of a left-flanking delimiter run and either
// (a) not part of a right-flanking delimiter run or
// (b) part of a right-flanking delimiter run preceded by a Unicode punctuation character.”
canOpen = leftFlank && (!rightFlank || isUnicodePunct(before))
// “A single _ character can close emphasis iff
// it is part of a right-flanking delimiter run and either
// (a) not part of a left-flanking delimiter run or
// (b) part of a left-flanking delimiter run followed by a Unicode punctuation character.”
// “A double __ can close strong emphasis iff
// it is part of a right-flanking delimiter run and either
// (a) not part of a left-flanking delimiter run or
// (b) part of a left-flanking delimiter run followed by a Unicode punctuation character.”
canClose = rightFlank && (!leftFlank || isUnicodePunct(after))
}
x = &emphPlain{
Plain: Plain{s[start:end]},
canOpen: canOpen,
canClose: canClose,
n: end - start,
}
return x, end, true