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// Copyright 2019 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 (
"fmt"
"log"
"strings"
)
// Unified returns a unified diff of the old and new strings.
// The old and new labels are the names of the old and new files.
// If the strings are equal, it returns the empty string.
func Unified(oldLabel, newLabel, old, new string) string {
edits := Strings(old, new)
unified, err := ToUnified(oldLabel, newLabel, old, edits)
if err != nil {
// Can't happen: edits are consistent.
log.Fatalf("internal error in diff.Unified: %v", err)
}
return unified
}
// ToUnified applies the edits to content and returns a unified diff.
// The old and new labels are the names of the content and result files.
// It returns an error if the edits are inconsistent; see ApplyEdits.
func ToUnified(oldLabel, newLabel, content string, edits []Edit) (string, error) {
u, err := toUnified(oldLabel, newLabel, content, edits)
if err != nil {
return "", err
}
return u.String(), nil
}
// unified represents a set of edits as a unified diff.
type unified struct {
// from is the name of the original file.
from string
// to is the name of the modified file.
to string
// hunks is the set of edit hunks needed to transform the file content.
hunks []*hunk
}
// Hunk represents a contiguous set of line edits to apply.
type hunk struct {
// The line in the original source where the hunk starts.
fromLine int
// The line in the original source where the hunk finishes.
toLine int
// The set of line based edits to apply.
lines []line
}
// Line represents a single line operation to apply as part of a Hunk.
type line struct {
// kind is the type of line this represents, deletion, insertion or copy.
kind opKind
// content is the content of this line.
// For deletion it is the line being removed, for all others it is the line
// to put in the output.
content string
}
// opKind is used to denote the type of operation a line represents.
type opKind int
const (
// opDelete is the operation kind for a line that is present in the input
// but not in the output.
opDelete opKind = iota
// opInsert is the operation kind for a line that is new in the output.
opInsert
// opEqual is the operation kind for a line that is the same in the input and
// output, often used to provide context around edited lines.
opEqual
)
// String returns a human readable representation of an OpKind. It is not
// intended for machine processing.
func (k opKind) String() string {
switch k {
case opDelete:
return "delete"
case opInsert:
return "insert"
case opEqual:
return "equal"
default:
panic("unknown operation kind")
}
}
const (
edge = 3
gap = edge * 2
)
// toUnified takes a file contents and a sequence of edits, and calculates
// a unified diff that represents those edits.
func toUnified(fromName, toName string, content string, edits []Edit) (unified, error) {
u := unified{
from: fromName,
to: toName,
}
if len(edits) == 0 {
return u, nil
}
var err error
edits, err = lineEdits(content, edits) // expand to whole lines
if err != nil {
return u, err
}
lines := splitLines(content)
var h *hunk
last := 0
toLine := 0
for _, edit := range edits {
// Compute the zero-based line numbers of the edit start and end.
// TODO(adonovan): opt: compute incrementally, avoid O(n^2).
start := strings.Count(content[:edit.Start], "\n")
end := strings.Count(content[:edit.End], "\n")
if edit.End == len(content) && len(content) > 0 && content[len(content)-1] != '\n' {
end++ // EOF counts as an implicit newline
}
switch {
case h != nil && start == last:
//direct extension
case h != nil && start <= last+gap:
//within range of previous lines, add the joiners
addEqualLines(h, lines, last, start)
default:
//need to start a new hunk
if h != nil {
// add the edge to the previous hunk
addEqualLines(h, lines, last, last+edge)
u.hunks = append(u.hunks, h)
}
toLine += start - last
h = &hunk{
fromLine: start + 1,
toLine: toLine + 1,
}
// add the edge to the new hunk
delta := addEqualLines(h, lines, start-edge, start)
h.fromLine -= delta
h.toLine -= delta
}
last = start
for i := start; i < end; i++ {
h.lines = append(h.lines, line{kind: opDelete, content: lines[i]})
last++
}
if edit.New != "" {
for _, content := range splitLines(edit.New) {
h.lines = append(h.lines, line{kind: opInsert, content: content})
toLine++
}
}
}
if h != nil {
// add the edge to the final hunk
addEqualLines(h, lines, last, last+edge)
u.hunks = append(u.hunks, h)
}
return u, nil
}
func splitLines(text string) []string {
lines := strings.SplitAfter(text, "\n")
if lines[len(lines)-1] == "" {
lines = lines[:len(lines)-1]
}
return lines
}
func addEqualLines(h *hunk, lines []string, start, end int) int {
delta := 0
for i := start; i < end; i++ {
if i < 0 {
continue
}
if i >= len(lines) {
return delta
}
h.lines = append(h.lines, line{kind: opEqual, content: lines[i]})
delta++
}
return delta
}
// String converts a unified diff to the standard textual form for that diff.
// The output of this function can be passed to tools like patch.
func (u unified) String() string {
if len(u.hunks) == 0 {
return ""
}
b := new(strings.Builder)
fmt.Fprintf(b, "--- %s\n", u.from)
fmt.Fprintf(b, "+++ %s\n", u.to)
for _, hunk := range u.hunks {
fromCount, toCount := 0, 0
for _, l := range hunk.lines {
switch l.kind {
case opDelete:
fromCount++
case opInsert:
toCount++
default:
fromCount++
toCount++
}
}
fmt.Fprint(b, "@@")
if fromCount > 1 {
fmt.Fprintf(b, " -%d,%d", hunk.fromLine, fromCount)
} else if hunk.fromLine == 1 && fromCount == 0 {
// Match odd GNU diff -u behavior adding to empty file.
fmt.Fprintf(b, " -0,0")
} else {
fmt.Fprintf(b, " -%d", hunk.fromLine)
}
if toCount > 1 {
fmt.Fprintf(b, " +%d,%d", hunk.toLine, toCount)
} else if hunk.toLine == 1 && toCount == 0 {
// Match odd GNU diff -u behavior adding to empty file.
fmt.Fprintf(b, " +0,0")
} else {
fmt.Fprintf(b, " +%d", hunk.toLine)
}
fmt.Fprint(b, " @@\n")
for _, l := range hunk.lines {
switch l.kind {
case opDelete:
fmt.Fprintf(b, "-%s", l.content)
case opInsert:
fmt.Fprintf(b, "+%s", l.content)
default:
fmt.Fprintf(b, " %s", l.content)
}
if !strings.HasSuffix(l.content, "\n") {
fmt.Fprintf(b, "\n\\ No newline at end of file\n")
}
}
}
return b.String()
}