[PATCH 2/2] vcs_info quilt: Extract a patch subject, 2.0.

[Daniel Shahaf <d.s@xxxxxxxxxxxxxxxxxx>]

---
 Functions/VCS_Info/VCS_INFO_quilt | 42 +++++++++++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/Functions/VCS_Info/VCS_INFO_quilt b/Functions/VCS_Info/VCS_INFO_quilt
index e31deb0..009c9d4 100644
--- a/Functions/VCS_Info/VCS_INFO_quilt
+++ b/Functions/VCS_Info/VCS_INFO_quilt
@@ -83,15 +83,49 @@ function VCS_INFO_quilt-dirfind() {
 # This function takes as an argument a filename of a patch and sets $REPLY to
 # a single-line "subject", or unsets it if no subject could be extracted.
 function VCS_INFO_quilt-patch2subject() {
-    local line
-    if [[ -f "$1" ]] && read -r line < "$1"; then
-        if [[ $line != (#b)(---|Index:)* ]]; then
-            REPLY=$line
+    integer i
+    integer -r LIMIT=10
+    local -a lines
+    local needle
+    if [[ -f "$1" ]]; then
+        # Extract the first LIMIT lines, or up to the first empty line or the start of the unidiffs,
+        # whichever comes first.
+        while (( i++ < LIMIT )); do
+            IFS= read -r "lines[$i]"
+            if [[ -z ${lines[$i]} ]] || [[ ${lines[$i]} == (#b)(---|Index:)* ]]; then
+                lines[$i]=()
+                break
+            fi
+        done < "$1"
+        
+        if needle=${lines[(i)Subject:*]}; (( needle <= $#lines )); then
+            # "Subject: foo" line, plus rfc822 whitespace unfolding.
+            #
+            # Example: 'git format-patch' patches.
+            REPLY=${lines[needle]}
+            REPLY=${REPLY#*: }
+            REPLY=${REPLY#\[PATCH\] }
+            while [[ ${${lines[++needle]}[1]} == ' ' ]]; do
+                REPLY+=${lines[needle]}
+            done
+        elif needle=${lines[(r)Description:*]}; [[ -n $needle ]]; then
+            # "Description: foo" line.
+            #
+            # Example: DEP-3 patches.
+            REPLY=${needle#*: }
+        elif [[ ${lines[1]} == '# HG changeset patch' ]] && { needle=${${lines:#([#]*)}[1]}; [[ -n $needle ]] }; then
+            # Mercurial patch
+            REPLY=$needle
+        elif (( $+lines[1] )); then
+            # The first line of the file is not part of the diff.
+            REPLY=${lines[1]}
         else
+            # The patch has no subject.
             unset REPLY
             return 0
         fi
     else
+        # The patch cannot be examined, or invalid arguments.
         unset REPLY
         return 1
     fi