hgmerge: logic changes

Details:
  - keep automatic merge conflicts in $LOCAL
  - do not assume that $EDITOR returns proper error code
  - fix a slight mistake in diff+patch merge success detection
    (it could succeed if the $EDITOR failed to run)

hgmerge

@@ -1,171 +1,159 b''
 #!/bin/sh
 #
 # hgmerge - default merge helper for Mercurial
 #
 # This tries to find a way to do three-way merge on the current system.
 # The result ought to end up in $1.
 
 set -e # bail out quickly on failure
 
 LOCAL="$1"
 BASE="$2"
 OTHER="$3"
 
 if [ -z "$EDITOR" ]; then
     EDITOR="vi"
 fi
 
 # find decent versions of our utilities, insisting on the GNU versions where we
 # need to
 MERGE="merge"
 DIFF3="gdiff3"
 DIFF="gdiff"
 PATCH="gpatch"
 
 type "$MERGE" >/dev/null 2>&1 || MERGE=
 type "$DIFF3" >/dev/null 2>&1 || DIFF3="diff3"
 $DIFF3 --version >/dev/null 2>&1 || DIFF3=
 type "$DIFF"  >/dev/null 2>&1 || DIFF="diff"
 type "$DIFF"  >/dev/null 2>&1 || DIFF=
 type "$PATCH" >/dev/null 2>&1 || PATCH="patch"
 type "$PATCH" >/dev/null 2>&1 || PATCH=
 
 # find optional visual utilities
 FILEMERGE="/Developer/Applications/Utilities/FileMerge.app/Contents/MacOS/FileMerge"
 KDIFF3="kdiff3"
 TKDIFF="tkdiff"
 
 type "$FILEMERGE" >/dev/null 2>&1 || FILEMERGE=
 type "$KDIFF3"    >/dev/null 2>&1 || KDIFF3=
 type "$TKDIFF"    >/dev/null 2>&1 || TKDIFF=
 
 # random part of names
 RAND="$RANDOM$RANDOM"
 
 # temporary directory for diff+patch merge
 HGTMP="${TMPDIR-'/tmp'}/hgmerge.$RAND"
 
 # backup file
 BACKUP="$LOCAL.orig.$RAND"
 
 # file used to test for file change
 CHGTEST="$LOCAL.chg.$RAND"
 
 # put all your required cleanup here
 cleanup() {
     rm -f "$BACKUP" "$CHGTEST"
     rm -rf "$HGTMP"
 }
 
 # functions concerning program exit
 success() {
     cleanup
     exit 0
 }
 
 failure() {
     echo "merge failed" 1>&2
     mv "$BACKUP" "$LOCAL"
     cleanup
     exit 1
 }
 
 # Ask if the merge was successful
 ask_if_merged() {
     while 1; do
         echo "$LOCAL seems unchanged. Was the merge successful? [y/n]"
         read answer
         case answer in
             y*|Y*) success;;
             n*|N*) failure;;
         esac
     done
 }
 
 # Clean up when interrupted
 trap "failure" 1 2 3 6 15 # HUP INT QUIT ABRT TERM
 
 # Back up our file (and try hard to keep the mtime unchanged)
 mv "$LOCAL" "$BACKUP"
 cp "$BACKUP" "$LOCAL"
 
 # Attempt to do a non-interactive merge
 if [ -n "$MERGE" -o -n "$DIFF3" ]; then
     if [ -n "$MERGE" ]; then
         $MERGE "$LOCAL" "$BASE" "$OTHER" 2> /dev/null && success
     elif [ -n "$DIFF3" ]; then
         $DIFF3 -m "$BACKUP" "$BASE" "$OTHER" > "$LOCAL" && success
     fi
     if [ $? -gt 1 ]; then
         echo "automatic merge failed! Exiting." 1>&2
         failure
     fi
 fi
-cp "$BACKUP" "$LOCAL"
 
 # on MacOS X try FileMerge.app, shipped with Apple's developer tools
 if [ -n "$FILEMERGE" ]; then
     cp "$BACKUP" "$LOCAL"
     cp "$BACKUP" "$CHGTEST"
     # filemerge prefers the right by default
     $FILEMERGE -left "$OTHER" -right "$LOCAL" -ancestor "$BASE" -merge "$LOCAL"
     [ $? -ne 0 ] && echo "FileMerge failed to launch" && failure
     test "$LOCAL" -nt "$CHGTEST" && success || ask_if_merged
-    failure
 fi
 
 if [ -n "$DISPLAY" ]; then
     # try using kdiff3, which is fairly nice
     if [ -n "$KDIFF3" ]; then
         $KDIFF3 --auto "$BASE" "$LOCAL" "$OTHER" -o "$LOCAL" || failure
         success
     fi
 
     # try using tkdiff, which is a bit less sophisticated
     if [ -n "$TKDIFF" ]; then
         $TKDIFF "$LOCAL" "$OTHER" -a "$BASE" -o "$LOCAL" || failure
         success
     fi
 fi
 
 # Attempt to do a merge with $EDITOR
-if [ -n "$MERGE" ]; then
-    echo "conflicts detected in $LOCAL"
-    $MERGE "$LOCAL" "$BASE" "$OTHER" 2>/dev/null || $EDITOR "$LOCAL"
-    success
-fi
-
-if [ -n "$DIFF3" ]; then
+if [ -n "$MERGE" -o -n "$DIFF3" ]; then
     echo "conflicts detected in $LOCAL"
-    $DIFF3 -m "$BACKUP" "$BASE" "$OTHER" > "$LOCAL" || {
-        case $? in
-            1)
-                $EDITOR "$LOCAL" ;;
-            2)  echo "$DIFF3 failed! Exiting." 1>&2
-                cp "$BACKUP" "$LOCAL"
-                failure ;;
-        esac
-        success
-    }
+    cp "$BACKUP" "$CHGTEST"
+    $EDITOR "$LOCAL" || failure
+    # Some editors do not return meaningful error codes
+    # Do not take any chances
+    test "$LOCAL" -nt "$CHGTEST" && success || ask_if_merged
 fi
 
 # attempt to manually merge with diff and patch
 if [ -n "$DIFF" -a -n "$PATCH" ]; then
 
     (umask 077 && mkdir "$HGTMP") || {
         echo "Could not create temporary directory $HGTMP" 1>&2
         failure
     }
 
     $DIFF -u "$BASE" "$OTHER" > "$HGTMP/diff" || :
     if $PATCH "$LOCAL" < "$HGTMP/diff"; then
         success
     else
         # If rejects are empty after using the editor, merge was ok
-        $EDITOR "$LOCAL" "$LOCAL.rej" && test -s "$LOCAL.rej" || success
+        $EDITOR "$LOCAL" "$LOCAL.rej" || failure
+        test -s "$LOCAL.rej" || success
     fi
     failure
 fi
 
 echo "hgmerge: unable to find merge, tkdiff, kdiff3, or diff+patch!"
 failure