Fix yet another bug with diff file names (#12771)

Following further testing it has become apparent that the diff line
cannot be used to determine filenames for diffs with any sort of predictability
the answer therefore is to use the other lines that are provided with a diff

Fix #12768

Signed-off-by: Andrew Thornton <art27@cantab.net>

2 files changed, 246 insertions, 50 deletions

diff --git a/services/gitdiff/gitdiff.go b/services/gitdiff/gitdiff.go
index 538f613b04..4cea5dd9a0 100644
--- a/services/gitdiff/gitdiff.go
+++ b/services/gitdiff/gitdiff.go
@@ -53,6 +53,7 @@ const (
 	DiffFileChange
 	DiffFileDel
 	DiffFileRename
+	DiffFileCopy
 )
 
 // DiffLineExpandDirection represents the DiffLineSection expand direction
@@ -481,7 +482,46 @@ func ParsePatch(maxLines, maxLineCharacters, maxFiles int, reader io.Reader) (*D
 		}
 		line := linebuf.String()
 
-		if strings.HasPrefix(line, "+++ ") || strings.HasPrefix(line, "--- ") || len(line) == 0 {
+		if strings.HasPrefix(line, "--- ") {
+			if line[4] == '"' {
+				fmt.Sscanf(line[4:], "%q", &curFile.OldName)
+			} else {
+				curFile.OldName = line[4:]
+				if strings.Contains(curFile.OldName, " ") {
+					// Git adds a terminal \t if there is a space in the name
+					curFile.OldName = curFile.OldName[:len(curFile.OldName)-1]
+				}
+			}
+			if curFile.OldName[0:2] == "a/" {
+				curFile.OldName = curFile.OldName[2:]
+			}
+			continue
+		} else if strings.HasPrefix(line, "+++ ") {
+			if line[4] == '"' {
+				fmt.Sscanf(line[4:], "%q", &curFile.Name)
+			} else {
+				curFile.Name = line[4:]
+				if strings.Contains(curFile.Name, " ") {
+					// Git adds a terminal \t if there is a space in the name
+					curFile.Name = curFile.Name[:len(curFile.Name)-1]
+				}
+			}
+			if curFile.Name[0:2] == "b/" {
+				curFile.Name = curFile.Name[2:]
+			}
+			curFile.IsRenamed = (curFile.Name != curFile.OldName) && !(curFile.IsCreated || curFile.IsDeleted)
+			if curFile.IsDeleted {
+				curFile.Name = curFile.OldName
+				curFile.OldName = ""
+			} else if curFile.IsCreated {
+				curFile.OldName = ""
+			}
+			continue
+		} else if len(line) == 0 {
+			continue
+		}
+
+		if strings.HasPrefix(line, "+++") || strings.HasPrefix(line, "---") || len(line) == 0 {
 			continue
 		}
 
@@ -569,36 +609,10 @@ func ParsePatch(maxLines, maxLineCharacters, maxFiles int, reader io.Reader) (*D
 				break
 			}
 
-			// Note: In case file name is surrounded by double quotes (it happens only in git-shell).
-			// e.g. diff --git "a/xxx" "b/xxx"
-			var a string
-			var b string
-
-			rd := strings.NewReader(line[len(cmdDiffHead):])
-			char, _ := rd.ReadByte()
-			_ = rd.UnreadByte()
-			if char == '"' {
-				fmt.Fscanf(rd, "%q ", &a)
-			} else {
-				fmt.Fscanf(rd, "%s ", &a)
-			}
-			char, _ = rd.ReadByte()
-			_ = rd.UnreadByte()
-			if char == '"' {
-				fmt.Fscanf(rd, "%q", &b)
-			} else {
-				fmt.Fscanf(rd, "%s", &b)
-			}
-			a = a[2:]
-			b = b[2:]
-
 			curFile = &DiffFile{
-				Name:      b,
-				OldName:   a,
-				Index:     len(diff.Files) + 1,
-				Type:      DiffFileChange,
-				Sections:  make([]*DiffSection, 0, 10),
-				IsRenamed: a != b,
+				Index:    len(diff.Files) + 1,
+				Type:     DiffFileChange,
+				Sections: make([]*DiffSection, 0, 10),
 			}
 			diff.Files = append(diff.Files, curFile)
 			curFileLinesCount = 0
@@ -607,6 +621,7 @@ func ParsePatch(maxLines, maxLineCharacters, maxFiles int, reader io.Reader) (*D
 			curFileLFSPrefix = false
 
 			// Check file diff type and is submodule.
+		loop:
 			for {
 				line, err := input.ReadString('\n')
 				if err != nil {
@@ -617,23 +632,67 @@ func ParsePatch(maxLines, maxLineCharacters, maxFiles int, reader io.Reader) (*D
 					}
 				}
 
-				switch {
-				case strings.HasPrefix(line, "new file"):
-					curFile.Type = DiffFileAdd
-					curFile.IsCreated = true
-				case strings.HasPrefix(line, "deleted"):
-					curFile.Type = DiffFileDel
-					curFile.IsDeleted = true
-				case strings.HasPrefix(line, "index"):
-					curFile.Type = DiffFileChange
-				case strings.HasPrefix(line, "similarity index 100%"):
-					curFile.Type = DiffFileRename
-				}
-				if curFile.Type > 0 {
-					if strings.HasSuffix(line, " 160000\n") {
-						curFile.IsSubmodule = true
+				if curFile.Type != DiffFileRename {
+					switch {
+					case strings.HasPrefix(line, "new file"):
+						curFile.Type = DiffFileAdd
+						curFile.IsCreated = true
+					case strings.HasPrefix(line, "deleted"):
+						curFile.Type = DiffFileDel
+						curFile.IsDeleted = true
+					case strings.HasPrefix(line, "index"):
+						curFile.Type = DiffFileChange
+					case strings.HasPrefix(line, "similarity index 100%"):
+						curFile.Type = DiffFileRename
+					}
+					if curFile.Type > 0 && curFile.Type != DiffFileRename {
+						if strings.HasSuffix(line, " 160000\n") {
+							curFile.IsSubmodule = true
+						}
+						break
+					}
+				} else {
+					switch {
+					case strings.HasPrefix(line, "rename from "):
+						if line[12] == '"' {
+							fmt.Sscanf(line[12:], "%q", &curFile.OldName)
+						} else {
+							curFile.OldName = line[12:]
+							curFile.OldName = curFile.OldName[:len(curFile.OldName)-1]
+						}
+					case strings.HasPrefix(line, "rename to "):
+						if line[10] == '"' {
+							fmt.Sscanf(line[10:], "%q", &curFile.Name)
+						} else {
+							curFile.Name = line[10:]
+							curFile.Name = curFile.Name[:len(curFile.Name)-1]
+						}
+						curFile.IsRenamed = true
+						break loop
+					case strings.HasPrefix(line, "copy from "):
+						if line[10] == '"' {
+							fmt.Sscanf(line[10:], "%q", &curFile.OldName)
+						} else {
+							curFile.OldName = line[10:]
+							curFile.OldName = curFile.OldName[:len(curFile.OldName)-1]
+						}
+					case strings.HasPrefix(line, "copy to "):
+						if line[8] == '"' {
+							fmt.Sscanf(line[8:], "%q", &curFile.Name)
+						} else {
+							curFile.Name = line[8:]
+							curFile.Name = curFile.Name[:len(curFile.Name)-1]
+						}
+						curFile.IsRenamed = true
+						curFile.Type = DiffFileCopy
+						break loop
+					default:
+						if strings.HasSuffix(line, " 160000\n") {
+							curFile.IsSubmodule = true
+						} else {
+							break loop
+						}
 					}
-					break
 				}
 			}
 		}
diff --git a/services/gitdiff/gitdiff_test.go b/services/gitdiff/gitdiff_test.go
index 9826ece2dc..ad1d186e73 100644
--- a/services/gitdiff/gitdiff_test.go
+++ b/services/gitdiff/gitdiff_test.go
@@ -6,6 +6,7 @@
 package gitdiff
 
 import (
+	"encoding/json"
 	"fmt"
 	"html/template"
 	"strings"
@@ -14,11 +15,9 @@ import (
 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/setting"
-
-	"gopkg.in/ini.v1"
-
 	dmp "github.com/sergi/go-diff/diffmatchpatch"
 	"github.com/stretchr/testify/assert"
+	"gopkg.in/ini.v1"
 )
 
 func assertEqual(t *testing.T, s1 string, s2 template.HTML) {
@@ -77,7 +76,145 @@ func TestDiffToHTML(t *testing.T) {
 	}, DiffLineAdd))
 }
 
-func TestParsePatch(t *testing.T) {
+func TestParsePatch_singlefile(t *testing.T) {
+	type testcase struct {
+		name        string
+		gitdiff     string
+		wantErr     bool
+		addition    int
+		deletion    int
+		oldFilename string
+		filename    string
+	}
+
+	tests := []testcase{
+		{
+			name: "readme.md2readme.md",
+			gitdiff: `diff --git "a/README.md" "b/README.md"
+--- a/README.md
++++ b/README.md
+@@ -1,3 +1,6 @@
+ # gitea-github-migrator
++
++ Build Status
+- Latest Release
+ Docker Pulls
++ cut off
++ cut off
+`,
+			addition: 4,
+			deletion: 1,
+			filename: "README.md",
+		},
+		{
+			name: "A \\ B",
+			gitdiff: `diff --git "a/A \\ B" "b/A \\ B"
+--- "a/A \\ B"
++++ "b/A \\ B"
+@@ -1,3 +1,6 @@
+ # gitea-github-migrator
++
++ Build Status
+- Latest Release
+ Docker Pulls
++ cut off
++ cut off`,
+			addition: 4,
+			deletion: 1,
+			filename: "A \\ B",
+		},
+		{
+			name: "really weird filename",
+			gitdiff: `diff --git a/a b/file b/a a/file b/a b/file b/a a/file
+index d2186f1..f5c8ed2 100644
+--- a/a b/file b/a a/file	
++++ b/a b/file b/a a/file	
+@@ -1,3 +1,2 @@
+ Create a weird file.
+ 
+-and what does diff do here?
+\ No newline at end of file`,
+			addition:    0,
+			deletion:    1,
+			filename:    "a b/file b/a a/file",
+			oldFilename: "a b/file b/a a/file",
+		},
+		{
+			name: "delete file with blanks",
+			gitdiff: `diff --git a/file with blanks b/file with blanks
+deleted file mode 100644
+index 898651a..0000000
+--- a/file with blanks	
++++ /dev/null
+@@ -1,5 +0,0 @@
+-a blank file
+-
+-has a couple o line
+-
+-the 5th line is the last
+`,
+			addition: 0,
+			deletion: 5,
+			filename: "file with blanks",
+		},
+		{
+			name: "rename a—as",
+			gitdiff: `diff --git "a/\360\243\220\265b\342\200\240vs" "b/a\342\200\224as"
+similarity index 100%
+rename from "\360\243\220\265b\342\200\240vs"
+rename to "a\342\200\224as"
+`,
+			addition:    0,
+			deletion:    0,
+			oldFilename: "𣐵b†vs",
+			filename:    "a—as",
+		},
+		{
+			name: "rename with spaces",
+			gitdiff: `diff --git a/a b/file b/a a/file b/a b/a a/file b/b file
+similarity index 100%
+rename from a b/file b/a a/file
+rename to a b/a a/file b/b file
+`,
+			oldFilename: "a b/file b/a a/file",
+			filename:    "a b/a a/file b/b file",
+		},
+	}
+
+	for _, testcase := range tests {
+		t.Run(testcase.name, func(t *testing.T) {
+			got, err := ParsePatch(setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(testcase.gitdiff))
+			if (err != nil) != testcase.wantErr {
+				t.Errorf("ParsePatch() error = %v, wantErr %v", err, testcase.wantErr)
+				return
+			}
+			gotMarshaled, _ := json.MarshalIndent(got, "  ", "  ")
+			if got.NumFiles != 1 {
+				t.Errorf("ParsePath() did not receive 1 file:\n%s", string(gotMarshaled))
+				return
+			}
+			if got.TotalAddition != testcase.addition {
+				t.Errorf("ParsePath() does not have correct totalAddition %d, wanted %d", got.TotalAddition, testcase.addition)
+			}
+			if got.TotalDeletion != testcase.deletion {
+				t.Errorf("ParsePath() did not have correct totalDeletion %d, wanted %d", got.TotalDeletion, testcase.deletion)
+			}
+			file := got.Files[0]
+			if file.Addition != testcase.addition {
+				t.Errorf("ParsePath() does not have correct file addition %d, wanted %d", file.Addition, testcase.addition)
+			}
+			if file.Deletion != testcase.deletion {
+				t.Errorf("ParsePath() did not have correct file deletion %d, wanted %d", file.Deletion, testcase.deletion)
+			}
+			if file.OldName != testcase.oldFilename {
+				t.Errorf("ParsePath() did not have correct OldName %s, wanted %s", file.OldName, testcase.oldFilename)
+			}
+			if file.Name != testcase.filename {
+				t.Errorf("ParsePath() did not have correct Name %s, wanted %s", file.Name, testcase.filename)
+			}
+		})
+	}
+
 	var diff = `diff --git "a/README.md" "b/README.md"
 --- a/README.md
 +++ b/README.md