Let cat_to_new_file handle the file backup

Let function cat_to_new_file optionally backup the destination file
before overwriting it. This has two advantages:
* This avoids duplicating code on the caller's side. Functions header
  and refresh both need to perform a backup.
* This guarantees the consistency of the backup logic. At the moment,
  the refresh command would handle the backup of a symlinked file
  just fine while the header command would misbehave in that case.

Now that the header command handles symlinked patches properly, also
test it so that we don't break it accidentally later.

4 files changed, 52 insertions, 12 deletions

diff --git a/quilt/header.in b/quilt/header.in
index a3bbcbc..6a9121f 100644
--- a/quilt/header.in
+++ b/quilt/header.in
@@ -159,9 +159,7 @@ else
 
 	cat_file "$patch_file_or_null" | patch_body >> $tmp2 || exit 1
 
-	if ( [ -z "$QUILT_BACKUP" -o ! -e $patch_file ] || \
-	       mv $patch_file $patch_file~ ) && \
-	       cat_to_new_file $patch_file < $tmp2
+	if cat_to_new_file $patch_file $QUILT_BACKUP < $tmp2
 	then
 		if [ -z "$opt_append" ]
 		then
diff --git a/quilt/refresh.in b/quilt/refresh.in
index aa9a2ae..a10659f 100644
--- a/quilt/refresh.in
+++ b/quilt/refresh.in
@@ -323,14 +323,7 @@ if [ -e "$patch_file" ] && \
    diff -q "$patch_file" $tmp_result > /dev/null
 then
 	printf $"Patch %s is unchanged\n" "$(print_patch "$patch")"
-elif ( [ -z "$QUILT_BACKUP" -o ! -e "$patch_file" ] || \
-       if [ -L "$patch_file" ] ; \
-       then \
-          cp -p "$patch_file" "$patch_file~"; \
-       else \
-          mv "$patch_file" "$patch_file~"; \
-       fi ) && \
-     cat_to_new_file "$patch_file" < $tmp_result
+elif cat_to_new_file "$patch_file" $QUILT_BACKUP < $tmp_result
 then
 	if [ -n "$opt_fork" ]
 	then
diff --git a/quilt/scripts/patchfns.in b/quilt/scripts/patchfns.in
index efb6e8e..ab4e725 100644
--- a/quilt/scripts/patchfns.in
+++ b/quilt/scripts/patchfns.in
@@ -783,7 +783,19 @@ cat_file()
 
 cat_to_new_file()
 {
-	local filename="$1"
+	local filename=$1 backup=$2
+
+	# If the file exists, back it up if requested. Return immediately upon
+	# failure.
+	if [ -e "$filename" -a -n "$backup" ]
+	then
+		if [ -L "$filename" ]
+		then
+			cp -p "$filename" "$filename~"
+		else
+			mv "$filename" "$filename~"
+		fi || return
+	fi
 
 	# If the destination file is a symbolic link, preserve it unless its
 	# target is read-only. In other cases, delete the patch file first in
diff --git a/test/symlink.test b/test/symlink.test
index a9fa45a..342ec10 100644
--- a/test/symlink.test
+++ b/test/symlink.test
@@ -55,6 +55,43 @@
 
 	$ [ patches/test.diff~ -nt test.timeref ] && echo "mtimes differ"
 
+# Test the header update
+	$ quilt header -a
+	< A test patch
+	> Appended text to header of patch patches/test.diff
+
+	$ readlink patches/test.diff
+	> ../test.diff
+
+# Test the header update with a backup
+	$ touch -r patches/test.diff test.timeref
+	$ quilt header -r --backup
+	> Replaced header of patch patches/test.diff
+
+	$ readlink patches/test.diff
+	> ../test.diff
+
+	$ cat patches/test.diff
+	> --- a/foo
+	> +++ b/foo
+	> @@ -1 +1 @@
+	> -foo
+	> +foo changed 3
+
+	$ readlink patches/test.diff~
+	$ echo %{?}
+	> 1
+
+	$ cat patches/test.diff~
+	> A test patch
+	> --- a/foo
+	> +++ b/foo
+	> @@ -1 +1 @@
+	> -foo
+	> +foo changed 3
+
+	$ [ patches/test.diff~ -nt test.timeref ] && echo "mtimes differ"
+
 # Test the refresh when target is read-only
 	$ chmod -w test.diff
 	$ echo "foo changed 4" > foo