+
+ set first_l [$ui_diff index "$first linestart"]
+ set last_l [$ui_diff index "$last lineend"]
+
+ if {$current_diff_path eq {} || $current_diff_header eq {}} return
+ if {![lock_index apply_hunk]} return
+
+ set apply_cmd {apply --cached --whitespace=nowarn}
+ set mi [lindex $file_states($current_diff_path) 0]
+ if {$current_diff_side eq $ui_index} {
+ set failed_msg [mc "Failed to unstage selected line."]
+ set to_context {+}
+ lappend apply_cmd --reverse
+ if {[string index $mi 0] ne {M}} {
+ unlock_index
+ return
+ }
+ } else {
+ set failed_msg [mc "Failed to stage selected line."]
+ set to_context {-}
+ if {[string index $mi 1] ne {M}} {
+ unlock_index
+ return
+ }
+ }
+
+ set wholepatch {}
+
+ while {$first_l < $last_l} {
+ set i_l [$ui_diff search -backwards -regexp ^@@ $first_l 0.0]
+ if {$i_l eq {}} {
+ # If there's not a @@ above, then the selected range
+ # must have come before the first_l @@
+ set i_l [$ui_diff search -regexp ^@@ $first_l $last_l]
+ }
+ if {$i_l eq {}} {
+ unlock_index
+ return
+ }
+ # $i_l is now at the beginning of a line
+
+ # pick start line number from hunk header
+ set hh [$ui_diff get $i_l "$i_l + 1 lines"]
+ set hh [lindex [split $hh ,] 0]
+ set hln [lindex [split $hh -] 1]
+
+ # There is a special situation to take care of. Consider this
+ # hunk:
+ #
+ # @@ -10,4 +10,4 @@
+ # context before
+ # -old 1
+ # -old 2
+ # +new 1
+ # +new 2
+ # context after
+ #
+ # We used to keep the context lines in the order they appear in
+ # the hunk. But then it is not possible to correctly stage only
+ # "-old 1" and "+new 1" - it would result in this staged text:
+ #
+ # context before
+ # old 2
+ # new 1
+ # context after
+ #
+ # (By symmetry it is not possible to *un*stage "old 2" and "new
+ # 2".)
+ #
+ # We resolve the problem by introducing an asymmetry, namely,
+ # when a "+" line is *staged*, it is moved in front of the
+ # context lines that are generated from the "-" lines that are
+ # immediately before the "+" block. That is, we construct this
+ # patch:
+ #
+ # @@ -10,4 +10,5 @@
+ # context before
+ # +new 1
+ # old 1
+ # old 2
+ # context after
+ #
+ # But we do *not* treat "-" lines that are *un*staged in a
+ # special way.
+ #
+ # With this asymmetry it is possible to stage the change "old
+ # 1" -> "new 1" directly, and to stage the change "old 2" ->
+ # "new 2" by first staging the entire hunk and then unstaging
+ # the change "old 1" -> "new 1".
+ #
+ # Applying multiple lines adds complexity to the special
+ # situation. The pre_context must be moved after the entire
+ # first block of consecutive staged "+" lines, so that
+ # staging both additions gives the following patch:
+ #
+ # @@ -10,4 +10,6 @@
+ # context before
+ # +new 1
+ # +new 2
+ # old 1
+ # old 2
+ # context after
+
+ # This is non-empty if and only if we are _staging_ changes;
+ # then it accumulates the consecutive "-" lines (after
+ # converting them to context lines) in order to be moved after
+ # "+" change lines.
+ set pre_context {}
+
+ set n 0
+ set m 0
+ set i_l [$ui_diff index "$i_l + 1 lines"]
+ set patch {}
+ while {[$ui_diff compare $i_l < "end - 1 chars"] &&
+ [$ui_diff get $i_l "$i_l + 2 chars"] ne {@@}} {
+ set next_l [$ui_diff index "$i_l + 1 lines"]
+ set c1 [$ui_diff get $i_l]
+ if {[$ui_diff compare $first_l <= $i_l] &&
+ [$ui_diff compare $i_l < $last_l] &&
+ ($c1 eq {-} || $c1 eq {+})} {
+ # a line to stage/unstage
+ set ln [$ui_diff get $i_l $next_l]
+ if {$c1 eq {-}} {
+ set n [expr $n+1]
+ set patch "$patch$pre_context$ln"
+ set pre_context {}
+ } else {
+ set m [expr $m+1]
+ set patch "$patch$ln"
+ }
+ } elseif {$c1 ne {-} && $c1 ne {+}} {
+ # context line
+ set ln [$ui_diff get $i_l $next_l]
+ set patch "$patch$pre_context$ln"
+ set n [expr $n+1]
+ set m [expr $m+1]
+ set pre_context {}
+ } elseif {$c1 eq $to_context} {
+ # turn change line into context line
+ set ln [$ui_diff get "$i_l + 1 chars" $next_l]
+ if {$c1 eq {-}} {
+ set pre_context "$pre_context $ln"
+ } else {
+ set patch "$patch $ln"
+ }
+ set n [expr $n+1]
+ set m [expr $m+1]
+ } else {
+ # a change in the opposite direction of
+ # to_context which is outside the range of
+ # lines to apply.
+ set patch "$patch$pre_context"
+ set pre_context {}
+ }
+ set i_l $next_l
+ }
+ set patch "$patch$pre_context"
+ set wholepatch "$wholepatch@@ -$hln,$n +$hln,$m @@\n$patch"
+ set first_l [$ui_diff index "$next_l + 1 lines"]
+ }
+
+ if {[catch {
+ set enc [get_path_encoding $current_diff_path]
+ set p [eval git_write $apply_cmd]
+ fconfigure $p -translation binary -encoding $enc
+ puts -nonewline $p $current_diff_header
+ puts -nonewline $p $wholepatch
+ close $p} err]} {
+ error_popup [append $failed_msg "\n\n$err"]
+ }
+
+ unlock_index