godoc: move bulk of the code to the package
R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/11424043
diff --git a/godoc/spec.go b/godoc/spec.go
new file mode 100644
index 0000000..6d6b9c2
--- /dev/null
+++ b/godoc/spec.go
@@ -0,0 +1,179 @@
+// 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:
+ 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:]
+ }
+}
