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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.
// 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.
package main
import (
"bytes"
"fmt"
"go/scanner"
"go/token"
"io"
"strings"
)
type ebnfParser struct {
out io.Writer // parser output
src []byte // parser source
scanner scanner.Scanner
prev int // offset of previous token
pos token.Position // token position
tok token.Token // one token look-ahead
lit []byte // token literal
}
func (p *ebnfParser) flush() {
p.out.Write(p.src[p.prev:p.pos.Offset])
p.prev = p.pos.Offset
}
func (p *ebnfParser) next() {
p.flush()
p.pos, p.tok, p.lit = p.scanner.Scan()
if p.tok.IsKeyword() {
// TODO Should keyword mapping always happen outside scanner?
// Or should there be a flag to scanner to enable keyword mapping?
p.tok = token.IDENT
}
}
func (p *ebnfParser) Error(pos token.Position, msg string) {
fmt.Fprintf(p.out, `<span class="alert">error: %s</span>`, msg)
}
func (p *ebnfParser) errorExpected(pos token.Position, msg string) {
msg = "expected " + msg
if pos.Offset == p.pos.Offset {
// the error happened at the current position;
// make the error message more specific
msg += ", found '" + p.tok.String() + "'"
if p.tok.IsLiteral() {
msg += " " + string(p.lit)
}
}
p.Error(pos, msg)
}
func (p *ebnfParser) expect(tok token.Token) token.Position {
pos := p.pos
if p.tok != tok {
p.errorExpected(pos, "'"+tok.String()+"'")
}
p.next() // make progress in any case
return pos
}
func (p *ebnfParser) parseIdentifier(def bool) {
name := string(p.lit)
p.expect(token.IDENT)
if def {
fmt.Fprintf(p.out, `<a id="%s">%s</a>`, name, name)
} else {
fmt.Fprintf(p.out, `<a href="#%s" class="noline">%s</a>`, name, name)
}
p.prev += len(name) // skip identifier when calling flush
}
func (p *ebnfParser) parseTerm() bool {
switch p.tok {
case token.IDENT:
p.parseIdentifier(false)
case token.STRING:
p.next()
if p.tok == token.ELLIPSIS {
p.next()
p.expect(token.STRING)
}
case token.LPAREN:
p.next()
p.parseExpression()
p.expect(token.RPAREN)
case token.LBRACK:
p.next()
p.parseExpression()
p.expect(token.RBRACK)
case token.LBRACE:
p.next()
p.parseExpression()
p.expect(token.RBRACE)
default:
return false
}
return true
}
func (p *ebnfParser) parseSequence() {
for p.parseTerm() {
}
}
func (p *ebnfParser) parseExpression() {
for {
p.parseSequence()
if p.tok != token.OR {
break
}
p.next()
}
}
func (p *ebnfParser) parseProduction() {
p.parseIdentifier(true)
p.expect(token.ASSIGN)
p.parseExpression()
p.expect(token.PERIOD)
}
func (p *ebnfParser) parse(out io.Writer, src []byte) {
// initialize ebnfParser
p.out = out
p.src = src
p.scanner.Init("", src, p, 0)
p.next() // initializes pos, tok, lit
// process source
for p.tok != token.EOF {
p.parseProduction()
}
p.flush()
}
// Markers around EBNF sections
var (
openTag = strings.Bytes(`<pre class="ebnf">`)
closeTag = strings.Bytes(`</pre>`)
)
func linkify(out io.Writer, src []byte) {
for len(src) > 0 {
n := len(src)
// i: beginning of EBNF text (or end of source)
i := bytes.Index(src, openTag)
if i < 0 {
i = n - len(openTag)
}
i += len(openTag)
// j: end of EBNF text (or end of source)
j := bytes.Index(src[i:n], closeTag) // close marker
if j < 0 {
j = n - i
}
j += i
// write text before EBNF
out.Write(src[0:i])
// parse and write EBNF
var p ebnfParser
p.parse(out, src[i:j])
// advance
src = src[j:n]
}
}
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