1 files changed, 198 insertions, 0 deletions
diff --git a/src/cmd/godoc/spec.go b/src/cmd/godoc/spec.go
new file mode 100644
index 000000000..3f69add86
--- /dev/null
+++ b/src/cmd/godoc/spec.go
@@ -0,0 +1,198 @@
+// 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"
+)
+
+type ebnfParser struct {
+	out     io.Writer   // parser output
+	src     []byte      // parser source
+	file    *token.File // for position information
+	scanner scanner.Scanner
+	prev    int         // offset of previous token
+	pos     token.Pos   // token position
+	tok     token.Token // one token look-ahead
+	lit     string      // token literal
+}
+
+func (p *ebnfParser) flush() {
+	offs := p.file.Offset(p.pos)
+	p.out.Write(p.src[p.prev:offs])
+	p.prev = offs
+}
+
+func (p *ebnfParser) next() {
+	if p.pos.IsValid() {
+		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.Pos, msg string) {
+	msg = "expected " + msg
+	if pos == p.pos {
+		// the error happened at the current position;
+		// make the error message more specific
+		msg += ", found '" + p.tok.String() + "'"
+		if p.tok.IsLiteral() {
+			msg += " " + p.lit
+		}
+	}
+	p.Error(p.file.Position(pos), msg)
+}
+
+func (p *ebnfParser) expect(tok token.Token) token.Pos {
+	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 := 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()
+		const ellipsis = "…" // U+2026, the horizontal ellipsis character
+		if p.tok == token.ILLEGAL && p.lit == 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() {
+	if !p.parseTerm() {
+		p.errorExpected(p.pos, "term")
+	}
+	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)
+	if p.tok != token.PERIOD {
+		p.parseExpression()
+	}
+	p.expect(token.PERIOD)
+}
+
+func (p *ebnfParser) parse(fset *token.FileSet, out io.Writer, src []byte) {
+	// initialize ebnfParser
+	p.out = out
+	p.src = src
+	p.file = fset.AddFile("", fset.Base(), len(src))
+	p.scanner.Init(p.file, src, p, scanner.AllowIllegalChars)
+	p.next() // initializes pos, tok, lit
+
+	// process source
+	for p.tok != token.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) {
+	fset := token.NewFileSet()
+	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(fset, out, src[i:j])
+
+		// advance
+		src = src[j:n]
+	}
+}