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// Copyright 2022 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 diff
import (
"strings"
"unicode/utf8"
"golang.org/x/tools/internal/diff/lcs"
"golang.org/x/tools/internal/span"
)
// maxDiffs is a limit on how deeply the lcs algorithm should search
// the value is just a guess
const maxDiffs = 30
// NComputeEdits computes TextEdits for strings
// (both it and the diff in the myers package have type ComputeEdits, which
// is why the arguments are strings, not []bytes.)
func NComputeEdits(uri span.URI, before, after string) ([]TextEdit, error) {
if before == after {
// very frequently true
return nil, nil
}
// the diffs returned by the lcs package use indexes into whatever slice
// was passed in. TextEdits need a span.Span which is computed with
// byte offsets, so rune or line offsets need to be converted.
if needrunes(before) || needrunes(after) {
diffs, _ := lcs.Compute([]rune(before), []rune(after), maxDiffs/2)
diffs = runeOffsets(diffs, []rune(before))
ans, err := convertDiffs(uri, diffs, []byte(before))
return ans, err
} else {
diffs, _ := lcs.Compute([]byte(before), []byte(after), maxDiffs/2)
ans, err := convertDiffs(uri, diffs, []byte(before))
return ans, err
}
}
// NComputeLineEdits computes TextEdits for []strings
func NComputeLineEdits(uri span.URI, before, after []string) ([]TextEdit, error) {
diffs, _ := lcs.Compute(before, after, maxDiffs/2)
diffs = lineOffsets(diffs, before)
ans, err := convertDiffs(uri, diffs, []byte(strJoin(before)))
// the code is not coping with possible missing \ns at the ends
return ans, err
}
// convert diffs with byte offsets into diffs with line and column
func convertDiffs(uri span.URI, diffs []lcs.Diff, src []byte) ([]TextEdit, error) {
ans := make([]TextEdit, len(diffs))
tf := span.NewTokenFile(uri.Filename(), src)
for i, d := range diffs {
s := newSpan(uri, d.Start, d.End)
s, err := s.WithPosition(tf)
if err != nil {
return nil, err
}
ans[i] = TextEdit{s, d.Text}
}
return ans, nil
}
// convert diffs with rune offsets into diffs with byte offsets
func runeOffsets(diffs []lcs.Diff, src []rune) []lcs.Diff {
var idx int
var tmp strings.Builder // string because []byte([]rune) is illegal
for i, d := range diffs {
tmp.WriteString(string(src[idx:d.Start]))
v := tmp.Len()
tmp.WriteString(string(src[d.Start:d.End]))
d.Start = v
idx = d.End
d.End = tmp.Len()
diffs[i] = d
}
return diffs
}
// convert diffs with line offsets into diffs with byte offsets
func lineOffsets(diffs []lcs.Diff, src []string) []lcs.Diff {
var idx int
var tmp strings.Builder // bytes/
for i, d := range diffs {
tmp.WriteString(strJoin(src[idx:d.Start]))
v := tmp.Len()
tmp.WriteString(strJoin(src[d.Start:d.End]))
d.Start = v
idx = d.End
d.End = tmp.Len()
diffs[i] = d
}
return diffs
}
// join lines. (strings.Join doesn't add a trailing separator)
func strJoin(elems []string) string {
if len(elems) == 0 {
return ""
}
n := 0
for i := 0; i < len(elems); i++ {
n += len(elems[i])
}
var b strings.Builder
b.Grow(n)
for _, s := range elems {
b.WriteString(s)
//b.WriteByte('\n')
}
return b.String()
}
func newSpan(uri span.URI, left, right int) span.Span {
return span.New(uri, span.NewPoint(0, 0, left), span.NewPoint(0, 0, right))
}
// need runes is true if the string needs to be converted to []rune
// for random access
func needrunes(s string) bool {
for i := 0; i < len(s); i++ {
if s[i] >= utf8.RuneSelf {
return true
}
}
return false
}