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// Copyright 2009 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 godoc
// This file contains the mechanism to "linkify" html source
// text containing EBNF sections (as found in go_spec.html).
// The result is the input source text with the EBNF sections
// modified such that identifiers are linked to the respective
// definitions.
import (
"bytes"
"fmt"
"io"
"text/scanner"
)
type ebnfParser struct {
out io.Writer // parser output
src []byte // parser input
scanner scanner.Scanner
prev int // offset of previous token
pos int // offset of current token
tok rune // one token look-ahead
lit string // token literal
}
func (p *ebnfParser) flush() {
p.out.Write(p.src[p.prev:p.pos])
p.prev = p.pos
}
func (p *ebnfParser) next() {
p.tok = p.scanner.Scan()
p.pos = p.scanner.Position.Offset
p.lit = p.scanner.TokenText()
}
func (p *ebnfParser) printf(format string, args ...interface{}) {
p.flush()
fmt.Fprintf(p.out, format, args...)
}
func (p *ebnfParser) errorExpected(msg string) {
p.printf(`<span class="highlight">error: expected %s, found %s</span>`, msg, scanner.TokenString(p.tok))
}
func (p *ebnfParser) expect(tok rune) {
if p.tok != tok {
p.errorExpected(scanner.TokenString(tok))
}
p.next() // make progress in any case
}
func (p *ebnfParser) parseIdentifier(def bool) {
if p.tok == scanner.Ident {
name := p.lit
if def {
p.printf(`<a id="%s">%s</a>`, name, name)
} else {
p.printf(`<a href="#%s" class="noline">%s</a>`, name, name)
}
p.prev += len(name) // skip identifier when printing next time
p.next()
} else {
p.expect(scanner.Ident)
}
}
func (p *ebnfParser) parseTerm() bool {
switch p.tok {
case scanner.Ident:
p.parseIdentifier(false)
case scanner.String, scanner.RawString:
p.next()
const ellipsis = '…' // U+2026, the horizontal ellipsis character
if p.tok == ellipsis {
p.next()
p.expect(scanner.String)
}
case '(':
p.next()
p.parseExpression()
p.expect(')')
case '[':
p.next()
p.parseExpression()
p.expect(']')
case '{':
p.next()
p.parseExpression()
p.expect('}')
default:
return false // no term found
}
return true
}
func (p *ebnfParser) parseSequence() {
if !p.parseTerm() {
p.errorExpected("term")
}
for p.parseTerm() {
}
}
func (p *ebnfParser) parseExpression() {
for {
p.parseSequence()
if p.tok != '|' {
break
}
p.next()
}
}
func (p *ebnfParser) parseProduction() {
p.parseIdentifier(true)
p.expect('=')
if p.tok != '.' {
p.parseExpression()
}
p.expect('.')
}
func (p *ebnfParser) parse(out io.Writer, src []byte) {
// initialize ebnfParser
p.out = out
p.src = src
p.scanner.Init(bytes.NewBuffer(src))
p.next() // initializes pos, tok, lit
// process source
for p.tok != scanner.EOF {
p.parseProduction()
}
p.flush()
}
// Markers around EBNF sections
var (
openTag = []byte(`<pre class="ebnf">`)
closeTag = []byte(`</pre>`)
)
func Linkify(out io.Writer, src []byte) {
for len(src) > 0 {
// i: beginning of EBNF text (or end of source)
i := bytes.Index(src, openTag)
if i < 0 {
i = len(src) - len(openTag)
}
i += len(openTag)
// j: end of EBNF text (or end of source)
j := bytes.Index(src[i:], closeTag) // close marker
if j < 0 {
j = len(src) - i
}
j += i
// write text before EBNF
out.Write(src[0:i])
// process EBNF
var p ebnfParser
p.parse(out, src[i:j])
// advance
src = src[j:]
}
}
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