simple euristic for further free packing improvements

diff --git a/git-checkout.sh b/git-checkout.sh
index 3bbd1117739b02572aece86030bb9f02f3110d34..a11c939c30f46561adb8179570d825a85fb8b57b 100755 (executable)
--- a/git-checkout.sh
+++ b/git-checkout.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-USAGE='[-f] [-b <new_branch>] [<branch>] [<paths>...]'
+USAGE='[-f] [-b <new_branch>] [-m] [<branch>] [<paths>...]'
 SUBDIRECTORY_OK=Sometimes
 . git-sh-setup
 
@@ -9,6 +9,7 @@ new=
 force=
 branch=
 newbranch=
+merge=
 while [ "$#" != "0" ]; do
     arg="$1"
     shift
@@ -21,11 +22,14 @@ while [ "$#" != "0" ]; do
                [ -e "$GIT_DIR/refs/heads/$newbranch" ] &&
                        die "git checkout: branch $newbranch already exists"
                git-check-ref-format "heads/$newbranch" ||
-                       die "we do not like '$newbranch' as a branch name."
+                       die "git checkout: we do not like '$newbranch' as a branch name."
                ;;
        "-f")
                force=1
                ;;
+       -m)
+               merge=1
+               ;;
        --)
                break
                ;;
@@ -71,9 +75,15 @@ done
 
 if test "$#" -ge 1
 then
-       if test '' != "$newbranch$force"
+       hint=
+       if test "$#" -eq 1
+       then
+               hint="
+Did you intend to checkout '$@' which can not be resolved as commit?"
+       fi
+       if test '' != "$newbranch$force$merge"
        then
-               die "updating paths and switching branches or forcing are incompatible."
+               die "git checkout: updating paths is incompatible with switching branches/forcing$hint"
        fi
        if test '' != "$new"
        then
@@ -113,7 +123,8 @@ fi
 
 [ -z "$branch$newbranch" ] &&
        [ "$new" != "$old" ] &&
-       die "git checkout: you need to specify a new branch name"
+       die "git checkout: to checkout the requested commit you need to specify 
+              a name for a new branch which is created and switched to"
 
 if [ "$force" ]
 then
@@ -121,7 +132,51 @@ then
        git-checkout-index -q -f -u -a
 else
     git-update-index --refresh >/dev/null
-    git-read-tree -m -u $old $new
+    merge_error=$(git-read-tree -m -u $old $new 2>&1) || (
+       case "$merge" in
+       '')
+               echo >&2 "$merge_error"
+               exit 1 ;;
+       esac
+
+       # Match the index to the working tree, and do a three-way.
+       git diff-files --name-only | git update-index --remove --stdin &&
+       work=`git write-tree` &&
+       git read-tree --reset $new &&
+       git checkout-index -f -u -q -a &&
+       git read-tree -m -u --aggressive $old $new $work || exit
+
+       if result=`git write-tree 2>/dev/null`
+       then
+           echo >&2 "Trivially automerged."
+       else
+           git merge-index -o git-merge-one-file -a
+       fi
+
+       # Do not register the cleanly merged paths in the index yet.
+       # this is not a real merge before committing, but just carrying
+       # the working tree changes along.
+       unmerged=`git ls-files -u`
+       git read-tree --reset $new
+       case "$unmerged" in
+       '')     ;;
+       *)
+               (
+                       z40=0000000000000000000000000000000000000000
+                       echo "$unmerged" |
+                       sed -e 's/^[0-7]* [0-9a-f]* /'"0 $z40 /"
+                       echo "$unmerged"
+               ) | git update-index --index-info
+               ;;
+       esac
+       exit 0
+    )
+    saved_err=$?
+    if test "$saved_err" = 0
+    then
+       test "$new" = "$old" || git diff-index --name-status "$new"
+    fi
+    (exit $saved_err)
 fi
 
 #