Read previous info from git blame (#28306) (#28310)

Backport #28306 by @KN4CK3R

Fixes #28280

Reads the `previous` info from the `git blame` output instead of
calculating it afterwards.

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

modules/git/blame.go

@@ -11,6 +11,7 @@ import (
 	"io"
 	"os"
 	"regexp"
+	"strings"
 
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/util"
@@ -18,8 +19,10 @@ import (
 
 // BlamePart represents block of blame - continuous lines with one sha
 type BlamePart struct {
-	Sha   string
-	Lines []string
+	Sha          string
+	Lines        []string
+	PreviousSha  string
+	PreviousPath string
 }
 
 // BlameReader returns part of file blame one by one
@@ -43,30 +46,38 @@ func (r *BlameReader) NextPart() (*BlamePart, error) {
 	var blamePart *BlamePart
 
 	if r.lastSha != nil {
-		blamePart = &BlamePart{*r.lastSha, make([]string, 0)}
+		blamePart = &BlamePart{
+			Sha:   *r.lastSha,
+			Lines: make([]string, 0),
+		}
 	}
 
-	var line []byte
+	var lineBytes []byte
 	var isPrefix bool
 	var err error
 
 	for err != io.EOF {
-		line, isPrefix, err = r.bufferedReader.ReadLine()
+		lineBytes, isPrefix, err = r.bufferedReader.ReadLine()
 		if err != nil && err != io.EOF {
 			return blamePart, err
 		}
 
-		if len(line) == 0 {
+		if len(lineBytes) == 0 {
 			// isPrefix will be false
 			continue
 		}
 
-		lines := shaLineRegex.FindSubmatch(line)
+		line := string(lineBytes)
+
+		lines := shaLineRegex.FindStringSubmatch(line)
 		if lines != nil {
-			sha1 := string(lines[1])
+			sha1 := lines[1]
 
 			if blamePart == nil {
-				blamePart = &BlamePart{sha1, make([]string, 0)}
+				blamePart = &BlamePart{
+					Sha:   sha1,
+					Lines: make([]string, 0),
+				}
 			}
 
 			if blamePart.Sha != sha1 {
@@ -81,9 +92,11 @@ func (r *BlameReader) NextPart() (*BlamePart, error) {
 				return blamePart, nil
 			}
 		} else if line[0] == '\t' {
-			code := line[1:]
-
-			blamePart.Lines = append(blamePart.Lines, string(code))
+			blamePart.Lines = append(blamePart.Lines, line[1:])
+		} else if strings.HasPrefix(line, "previous ") {
+			parts := strings.SplitN(line[len("previous "):], " ", 2)
+			blamePart.PreviousSha = parts[0]
+			blamePart.PreviousPath = parts[1]
 		}
 
 		// need to munch to end of line...

modules/git/blame_test.go

@@ -24,15 +24,17 @@ func TestReadingBlameOutput(t *testing.T) {
 
 		parts := []*BlamePart{
 			{
-				"72866af952e98d02a73003501836074b286a78f6",
-				[]string{
+				Sha: "72866af952e98d02a73003501836074b286a78f6",
+				Lines: []string{
 					"# test_repo",
 					"Test repository for testing migration from github to gitea",
 				},
 			},
 			{
-				"f32b0a9dfd09a60f616f29158f772cedd89942d2",
-				[]string{"", "Do not make any changes to this repo it is used for unit testing"},
+				Sha:          "f32b0a9dfd09a60f616f29158f772cedd89942d2",
+				Lines:        []string{"", "Do not make any changes to this repo it is used for unit testing"},
+				PreviousSha:  "72866af952e98d02a73003501836074b286a78f6",
+				PreviousPath: "README.md",
 			},
 		}
 
@@ -64,16 +66,18 @@ func TestReadingBlameOutput(t *testing.T) {
 
 		full := []*BlamePart{
 			{
-				"af7486bd54cfc39eea97207ca666aa69c9d6df93",
-				[]string{"line", "line"},
+				Sha:   "af7486bd54cfc39eea97207ca666aa69c9d6df93",
+				Lines: []string{"line", "line"},
 			},
 			{
-				"45fb6cbc12f970b04eacd5cd4165edd11c8d7376",
-				[]string{"changed line"},
+				Sha:          "45fb6cbc12f970b04eacd5cd4165edd11c8d7376",
+				Lines:        []string{"changed line"},
+				PreviousSha:  "af7486bd54cfc39eea97207ca666aa69c9d6df93",
+				PreviousPath: "blame.txt",
 			},
 			{
-				"af7486bd54cfc39eea97207ca666aa69c9d6df93",
-				[]string{"line", "line", ""},
+				Sha:   "af7486bd54cfc39eea97207ca666aa69c9d6df93",
+				Lines: []string{"line", "line", ""},
 			},
 		}
 
@@ -89,8 +93,8 @@ func TestReadingBlameOutput(t *testing.T) {
 				Bypass:         false,
 				Parts: []*BlamePart{
 					{
-						"af7486bd54cfc39eea97207ca666aa69c9d6df93",
-						[]string{"line", "line", "changed line", "line", "line", ""},
+						Sha:   "af7486bd54cfc39eea97207ca666aa69c9d6df93",
+						Lines: []string{"line", "line", "changed line", "line", "line", ""},
 					},
 				},
 			},