Fix mode on index lines, add more test cases

Author: bluekeyes

gitdiff/gitdiff.go

@@ -119,9 +119,12 @@ func (f *File) String() string {
 
 	if f.OldOIDPrefix != "" && f.NewOIDPrefix != "" {
 		fmt.Fprintf(&diff, "index %s..%s", f.OldOIDPrefix, f.NewOIDPrefix)
-		if f.OldMode != 0 && !f.IsDelete {
+
+		// Mode is only included on the index line when it is not changing
+		if f.OldMode != 0 && ((f.NewMode == 0 && !f.IsDelete) || f.OldMode == f.NewMode) {
 			fmt.Fprintf(&diff, " %o", f.OldMode)
 		}
+
 		diff.WriteByte('\n')
 	}
 

gitdiff/gitdiff_string_test.go

@@ -8,14 +8,17 @@ import (
 
 func TestFile_String(t *testing.T) {
 	sources := []string{
+		"testdata/string/copy.patch",
 		"testdata/string/delete.patch",
 		"testdata/string/mode.patch",
+		"testdata/string/mode_modify.patch",
 		"testdata/string/modify.patch",
 		"testdata/string/new.patch",
 		"testdata/string/new_empty.patch",
 		"testdata/string/new_mode.patch",
 		"testdata/string/rename.patch",
 		"testdata/string/rename_modify.patch",
+		"testdata/string/copy_modify.patch",
 	}
 
 	for _, src := range sources {

gitdiff/testdata/string/copy.patch

@@ -0,0 +1,4 @@
+diff --git a/file.txt b/numbers.txt
+similarity index 100%
+copy from file.txt
+copy to numbers.txt

gitdiff/testdata/string/copy_modify.patch

@@ -0,0 +1,21 @@
+diff --git a/file.txt b/numbers.txt
+similarity index 57%
+copy from file.txt
+copy to numbers.txt
+index c9e9e05..6c4a3e0 100644
+--- a/file.txt
++++ b/numbers.txt
+@@ -1,6 +1,6 @@
+ one
+ two
+-three
++three three three
+ four
+ five
+ six
+@@ -8,3 +8,5 @@ seven
+ eight
+ nine
+ ten
++eleven
++twelve

gitdiff/testdata/string/mode_modify.patch

@@ -0,0 +1,10 @@
+diff --git a/script.sh b/script.sh
+old mode 100644
+new mode 100755
+index 7a870bd..68d501e
+--- a/script.sh
++++ b/script.sh
+@@ -1,2 +1,2 @@
+ #!/bin/bash
+-echo "Hello World"
++echo "Hello, World!"