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// Copyright 2011 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 implements FormatSelections and FormatText.
// FormatText is used to HTML-format Go and non-Go source
// text with line numbers and highlighted sections. It is
// built on top of FormatSelections, a generic formatter
// for "selected" text.
package main
import (
"fmt"
"go/scanner"
"go/token"
"io"
"regexp"
"strconv"
"text/template"
)
// ----------------------------------------------------------------------------
// Implementation of FormatSelections
// A Selection is a function returning offset pairs []int{a, b}
// describing consecutive non-overlapping text segments [a, b).
// If there are no more segments, a Selection must return nil.
//
// TODO It's more efficient to return a pair (a, b int) instead
// of creating lots of slices. Need to determine how to
// indicate the end of a Selection.
//
type Selection func() []int
// A LinkWriter writes some start or end "tag" to w for the text offset offs.
// It is called by FormatSelections at the start or end of each link segment.
//
type LinkWriter func(w io.Writer, offs int, start bool)
// A SegmentWriter formats a text according to selections and writes it to w.
// The selections parameter is a bit set indicating which selections provided
// to FormatSelections overlap with the text segment: If the n'th bit is set
// in selections, the n'th selection provided to FormatSelections is overlapping
// with the text.
//
type SegmentWriter func(w io.Writer, text []byte, selections int)
// FormatSelections takes a text and writes it to w using link and segment
// writers lw and sw as follows: lw is invoked for consecutive segment starts
// and ends as specified through the links selection, and sw is invoked for
// consecutive segments of text overlapped by the same selections as specified
// by selections. The link writer lw may be nil, in which case the links
// Selection is ignored.
//
func FormatSelections(w io.Writer, text []byte, lw LinkWriter, links Selection, sw SegmentWriter, selections ...Selection) {
// If we have a link writer, make the links
// selection the last entry in selections
if lw != nil {
selections = append(selections, links)
}
// compute the sequence of consecutive segment changes
changes := newMerger(selections)
// The i'th bit in bitset indicates that the text
// at the current offset is covered by selections[i].
bitset := 0
lastOffs := 0
// Text segments are written in a delayed fashion
// such that consecutive segments belonging to the
// same selection can be combined (peephole optimization).
// last describes the last segment which has not yet been written.
var last struct {
begin, end int // valid if begin < end
bitset int
}
// flush writes the last delayed text segment
flush := func() {
if last.begin < last.end {
sw(w, text[last.begin:last.end], last.bitset)
}
last.begin = last.end // invalidate last
}
// segment runs the segment [lastOffs, end) with the selection
// indicated by bitset through the segment peephole optimizer.
segment := func(end int) {
if lastOffs < end { // ignore empty segments
if last.end != lastOffs || last.bitset != bitset {
// the last segment is not adjacent to or
// differs from the new one
flush()
// start a new segment
last.begin = lastOffs
}
last.end = end
last.bitset = bitset
}
}
for {
// get the next segment change
index, offs, start := changes.next()
if index < 0 || offs > len(text) {
// no more segment changes or the next change
// is past the end of the text - we're done
break
}
// determine the kind of segment change
if lw != nil && index == len(selections)-1 {
// we have a link segment change (see start of this function):
// format the previous selection segment, write the
// link tag and start a new selection segment
segment(offs)
flush()
lastOffs = offs
lw(w, offs, start)
} else {
// we have a selection change:
// format the previous selection segment, determine
// the new selection bitset and start a new segment
segment(offs)
lastOffs = offs
mask := 1 << uint(index)
if start {
bitset |= mask
} else {
bitset &^= mask
}
}
}
segment(len(text))
flush()
}
// A merger merges a slice of Selections and produces a sequence of
// consecutive segment change events through repeated next() calls.
//
type merger struct {
selections []Selection
segments [][]int // segments[i] is the next segment of selections[i]
}
const infinity int = 2e9
func newMerger(selections []Selection) *merger {
segments := make([][]int, len(selections))
for i, sel := range selections {
segments[i] = []int{infinity, infinity}
if sel != nil {
if seg := sel(); seg != nil {
segments[i] = seg
}
}
}
return &merger{selections, segments}
}
// next returns the next segment change: index specifies the Selection
// to which the segment belongs, offs is the segment start or end offset
// as determined by the start value. If there are no more segment changes,
// next returns an index value < 0.
//
func (m *merger) next() (index, offs int, start bool) {
// find the next smallest offset where a segment starts or ends
offs = infinity
index = -1
for i, seg := range m.segments {
switch {
case seg[0] < offs:
offs = seg[0]
index = i
start = true
case seg[1] < offs:
offs = seg[1]
index = i
start = false
}
}
if index < 0 {
// no offset found => all selections merged
return
}
// offset found - it's either the start or end offset but
// either way it is ok to consume the start offset: set it
// to infinity so it won't be considered in the following
// next call
m.segments[index][0] = infinity
if start {
return
}
// end offset found - consume it
m.segments[index][1] = infinity
// advance to the next segment for that selection
seg := m.selections[index]()
if seg == nil {
return
}
m.segments[index] = seg
return
}
// ----------------------------------------------------------------------------
// Implementation of FormatText
// lineSelection returns the line segments for text as a Selection.
func lineSelection(text []byte) Selection {
i, j := 0, 0
return func() (seg []int) {
// find next newline, if any
for j < len(text) {
j++
if text[j-1] == '\n' {
break
}
}
if i < j {
// text[i:j] constitutes a line
seg = []int{i, j}
i = j
}
return
}
}
// commentSelection returns the sequence of consecutive comments
// in the Go src text as a Selection.
//
func commentSelection(src []byte) Selection {
var s scanner.Scanner
fset := token.NewFileSet()
file := fset.AddFile("", fset.Base(), len(src))
s.Init(file, src, nil, scanner.ScanComments)
return func() (seg []int) {
for {
pos, tok, lit := s.Scan()
if tok == token.EOF {
break
}
offs := file.Offset(pos)
if tok == token.COMMENT {
seg = []int{offs, offs + len(lit)}
break
}
}
return
}
}
// makeSelection is a helper function to make a Selection from a slice of pairs.
func makeSelection(matches [][]int) Selection {
return func() (seg []int) {
if len(matches) > 0 {
seg = matches[0]
matches = matches[1:]
}
return
}
}
// regexpSelection computes the Selection for the regular expression expr in text.
func regexpSelection(text []byte, expr string) Selection {
var matches [][]int
if rx, err := regexp.Compile(expr); err == nil {
matches = rx.FindAllIndex(text, -1)
}
return makeSelection(matches)
}
var selRx = regexp.MustCompile(`^([0-9]+):([0-9]+)`)
// rangeSelection computes the Selection for a text range described
// by the argument str; the range description must match the selRx
// regular expression.
//
func rangeSelection(str string) Selection {
m := selRx.FindStringSubmatch(str)
if len(m) >= 2 {
from, _ := strconv.Atoi(m[1])
to, _ := strconv.Atoi(m[2])
if from < to {
return makeSelection([][]int{{from, to}})
}
}
return nil
}
// Span tags for all the possible selection combinations that may
// be generated by FormatText. Selections are indicated by a bitset,
// and the value of the bitset specifies the tag to be used.
//
// bit 0: comments
// bit 1: highlights
// bit 2: selections
//
var startTags = [][]byte{
/* 000 */ []byte(``),
/* 001 */ []byte(`<span class="comment">`),
/* 010 */ []byte(`<span class="highlight">`),
/* 011 */ []byte(`<span class="highlight-comment">`),
/* 100 */ []byte(`<span class="selection">`),
/* 101 */ []byte(`<span class="selection-comment">`),
/* 110 */ []byte(`<span class="selection-highlight">`),
/* 111 */ []byte(`<span class="selection-highlight-comment">`),
}
var endTag = []byte(`</span>`)
func selectionTag(w io.Writer, text []byte, selections int) {
if selections < len(startTags) {
if tag := startTags[selections]; len(tag) > 0 {
w.Write(tag)
template.HTMLEscape(w, text)
w.Write(endTag)
return
}
}
template.HTMLEscape(w, text)
}
// FormatText HTML-escapes text and writes it to w.
// Consecutive text segments are wrapped in HTML spans (with tags as
// defined by startTags and endTag) as follows:
//
// - if line >= 0, line number (ln) spans are inserted before each line,
// starting with the value of line
// - if the text is Go source, comments get the "comment" span class
// - each occurrence of the regular expression pattern gets the "highlight"
// span class
// - text segments covered by selection get the "selection" span class
//
// Comments, highlights, and selections may overlap arbitrarily; the respective
// HTML span classes are specified in the startTags variable.
//
func FormatText(w io.Writer, text []byte, line int, goSource bool, pattern string, selection Selection) {
var comments, highlights Selection
if goSource {
comments = commentSelection(text)
}
if pattern != "" {
highlights = regexpSelection(text, pattern)
}
if line >= 0 || comments != nil || highlights != nil || selection != nil {
var lineTag LinkWriter
if line >= 0 {
lineTag = func(w io.Writer, _ int, start bool) {
if start {
fmt.Fprintf(w, "<a id=\"L%d\"></a><span class=\"ln\">%6d</span>\t", line, line)
line++
}
}
}
FormatSelections(w, text, lineTag, lineSelection(text), selectionTag, comments, highlights, selection)
} else {
template.HTMLEscape(w, text)
}
}