git-gui: Refactor branch switch to support detached head

This is a major rewrite of the way we perform switching between
branches and the subsequent update of the working directory.  Like
core Git we now use a single code path to perform all changes: our
new checkout_op class.  We also use it for branch creation/update
as it integrates the tracking branch fetch process along with a
very basic merge (fast-forward and reset only currently).

Because some users have literally hundreds of local branches we
use the standard revision picker (with its branch filtering tool)
to select the local branch, rather than keeping all of the local
branches in the Branch menu.  The branch menu listing out all of
the available branches is simply not sane for those types of huge
repositories.

Users can now checkout a detached head by ticking off the option
in the checkout dialog.  This option is off by default for the
obvious reason, but it can be easily enabled for any local branch
by simply checking it.  We also detach the head if any non local
branch was selected, or if a revision expression was entered.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

10 files changed, 727 insertions, 436 deletions

diff --git a/lib/branch.tcl b/lib/branch.tcl
index a6e6921174..b948d926ae 100644
--- a/lib/branch.tcl
+++ b/lib/branch.tcl
@@ -2,7 +2,6 @@
 # Copyright (C) 2006, 2007 Shawn Pearce
 
 proc load_all_heads {} {
-	global all_heads
 	global some_heads_tracking
 
 	set rh refs/heads
@@ -16,7 +15,7 @@ proc load_all_heads {} {
 	}
 	close $fd
 
-	set all_heads [lsort $all_heads]
+	return [lsort $all_heads]
 }
 
 proc load_all_tags {} {
@@ -30,173 +29,7 @@ proc load_all_tags {} {
 	return $all_tags
 }
 
-proc populate_branch_menu {} {
-	global all_heads disable_on_lock
-
-	set m .mbar.branch
-	set last [$m index last]
-	for {set i 0} {$i <= $last} {incr i} {
-		if {[$m type $i] eq {separator}} {
-			$m delete $i last
-			set new_dol [list]
-			foreach a $disable_on_lock {
-				if {[lindex $a 0] ne $m || [lindex $a 2] < $i} {
-					lappend new_dol $a
-				}
-			}
-			set disable_on_lock $new_dol
-			break
-		}
-	}
-
-	if {$all_heads ne {}} {
-		$m add separator
-	}
-	foreach b $all_heads {
-		$m add radiobutton \
-			-label $b \
-			-command [list switch_branch $b] \
-			-variable current_branch \
-			-value $b
-		lappend disable_on_lock \
-			[list $m entryconf [$m index last] -state]
-	}
-}
-
 proc radio_selector {varname value args} {
 	upvar #0 $varname var
 	set var $value
 }
-
-proc switch_branch {new_branch} {
-	global HEAD commit_type current_branch repo_config
-
-	if {![lock_index switch]} return
-
-	# -- Our in memory state should match the repository.
-	#
-	repository_state curType curHEAD curMERGE_HEAD
-	if {[string match amend* $commit_type]
-		&& $curType eq {normal}
-		&& $curHEAD eq $HEAD} {
-	} elseif {$commit_type ne $curType || $HEAD ne $curHEAD} {
-		info_popup {Last scanned state does not match repository state.
-
-Another Git program has modified this repository since the last scan.  A rescan must be performed before the current branch can be changed.
-
-The rescan will be automatically started now.
-}
-		unlock_index
-		rescan {set ui_status_value {Ready.}}
-		return
-	}
-
-	# -- Don't do a pointless switch.
-	#
-	if {$current_branch eq $new_branch} {
-		unlock_index
-		return
-	}
-
-	if {$repo_config(gui.trustmtime) eq {true}} {
-		switch_branch_stage2 {} $new_branch
-	} else {
-		set ui_status_value {Refreshing file status...}
-		set cmd [list git update-index]
-		lappend cmd -q
-		lappend cmd --unmerged
-		lappend cmd --ignore-missing
-		lappend cmd --refresh
-		set fd_rf [open "| $cmd" r]
-		fconfigure $fd_rf -blocking 0 -translation binary
-		fileevent $fd_rf readable \
-			[list switch_branch_stage2 $fd_rf $new_branch]
-	}
-}
-
-proc switch_branch_stage2 {fd_rf new_branch} {
-	global ui_status_value HEAD
-
-	if {$fd_rf ne {}} {
-		read $fd_rf
-		if {![eof $fd_rf]} return
-		close $fd_rf
-	}
-
-	set ui_status_value "Updating working directory to '$new_branch'..."
-	set cmd [list git read-tree]
-	lappend cmd -m
-	lappend cmd -u
-	lappend cmd --exclude-per-directory=.gitignore
-	lappend cmd $HEAD
-	lappend cmd $new_branch
-	set fd_rt [open "| $cmd" r]
-	fconfigure $fd_rt -blocking 0 -translation binary
-	fileevent $fd_rt readable \
-		[list switch_branch_readtree_wait $fd_rt $new_branch]
-}
-
-proc switch_branch_readtree_wait {fd_rt new_branch} {
-	global selected_commit_type commit_type HEAD MERGE_HEAD PARENT
-	global current_branch
-	global ui_comm ui_status_value
-
-	# -- We never get interesting output on stdout; only stderr.
-	#
-	read $fd_rt
-	fconfigure $fd_rt -blocking 1
-	if {![eof $fd_rt]} {
-		fconfigure $fd_rt -blocking 0
-		return
-	}
-
-	# -- The working directory wasn't in sync with the index and
-	#    we'd have to overwrite something to make the switch. A
-	#    merge is required.
-	#
-	if {[catch {close $fd_rt} err]} {
-		regsub {^fatal: } $err {} err
-		warn_popup "File level merge required.
-
-$err
-
-Staying on branch '$current_branch'."
-		set ui_status_value "Aborted checkout of '$new_branch' (file level merging is required)."
-		unlock_index
-		return
-	}
-
-	# -- Update the symbolic ref.  Core git doesn't even check for failure
-	#    here, it Just Works(tm).  If it doesn't we are in some really ugly
-	#    state that is difficult to recover from within git-gui.
-	#
-	if {[catch {git symbolic-ref HEAD "refs/heads/$new_branch"} err]} {
-		error_popup "Failed to set current branch.
-
-This working directory is only partially switched.  We successfully updated your files, but failed to update an internal Git file.
-
-This should not have occurred.  [appname] will now close and give up.
-
-$err"
-		do_quit
-		return
-	}
-
-	# -- Update our repository state.  If we were previously in amend mode
-	#    we need to toss the current buffer and do a full rescan to update
-	#    our file lists.  If we weren't in amend mode our file lists are
-	#    accurate and we can avoid the rescan.
-	#
-	unlock_index
-	set selected_commit_type new
-	if {[string match amend* $commit_type]} {
-		$ui_comm delete 0.0 end
-		$ui_comm edit reset
-		$ui_comm edit modified false
-		rescan {set ui_status_value "Checked out branch '$current_branch'."}
-	} else {
-		repository_state commit_type HEAD MERGE_HEAD
-		set PARENT $HEAD
-		set ui_status_value "Checked out branch '$current_branch'."
-	}
-}
diff --git a/lib/branch_checkout.tcl b/lib/branch_checkout.tcl
new file mode 100644
index 0000000000..62230efe43
--- /dev/null
+++ b/lib/branch_checkout.tcl
@@ -0,0 +1,88 @@
+# git-gui branch checkout support
+# Copyright (C) 2007 Shawn Pearce
+
+class branch_checkout {
+
+field w              ; # widget path
+field w_rev          ; # mega-widget to pick the initial revision
+
+field opt_fetch     1; # refetch tracking branch if used?
+field opt_detach    0; # force a detached head case?
+
+constructor dialog {} {
+	make_toplevel top w
+	wm title $top "[appname] ([reponame]): Checkout Branch"
+	if {$top ne {.}} {
+		wm geometry $top "+[winfo rootx .]+[winfo rooty .]"
+	}
+
+	label $w.header -text {Checkout Branch} -font font_uibold
+	pack $w.header -side top -fill x
+
+	frame $w.buttons
+	button $w.buttons.create -text Checkout \
+		-default active \
+		-command [cb _checkout]
+	pack $w.buttons.create -side right
+	button $w.buttons.cancel -text {Cancel} \
+		-command [list destroy $w]
+	pack $w.buttons.cancel -side right -padx 5
+	pack $w.buttons -side bottom -fill x -pady 10 -padx 10
+
+	set w_rev [::choose_rev::new $w.rev {Revision}]
+	pack $w.rev -anchor nw -fill both -expand 1 -pady 5 -padx 5
+
+	labelframe $w.options -text {Options}
+
+	checkbutton $w.options.fetch \
+		-text {Fetch Tracking Branch} \
+		-variable @opt_fetch
+	pack $w.options.fetch -anchor nw
+
+	checkbutton $w.options.detach \
+		-text {Detach From Local Branch} \
+		-variable @opt_detach
+	pack $w.options.detach -anchor nw
+
+	pack $w.options -anchor nw -fill x -pady 5 -padx 5
+
+	bind $w <Visibility> [cb _visible]
+	bind $w <Key-Escape> [list destroy $w]
+	bind $w <Key-Return> [cb _checkout]\;break
+	tkwait window $w
+}
+
+method _checkout {} {
+	set spec [$w_rev get_tracking_branch]
+	if {$spec ne {} && $opt_fetch} {
+		set new {}
+	} elseif {[catch {set new [$w_rev commit_or_die]}]} {
+		return
+	}
+
+	if {$opt_detach} {
+		set ref {}
+	} else {
+		set ref [$w_rev get_local_branch]
+	}
+
+	set co [::checkout_op::new [$w_rev get] $new $ref]
+	$co parent $w
+	$co enable_checkout 1
+	if {$spec ne {} && $opt_fetch} {
+		$co enable_fetch $spec
+	}
+
+	if {[$co run]} {
+		destroy $w
+	} else {
+		$w_rev focus_filter
+	}
+}
+
+method _visible {} {
+	grab $w
+	$w_rev focus_filter
+}
+
+}
diff --git a/lib/branch_create.tcl b/lib/branch_create.tcl
index f708957b22..def615d19d 100644
--- a/lib/branch_create.tcl
+++ b/lib/branch_create.tcl
@@ -73,7 +73,7 @@ constructor dialog {} {
 	pack $w.options.merge.l -side left
 	radiobutton $w.options.merge.no \
 		-text No \
-		-value no \
+		-value none \
 		-variable @opt_merge
 	pack $w.options.merge.no -side left
 	radiobutton $w.options.merge.ff \
@@ -113,7 +113,7 @@ constructor dialog {} {
 }
 
 method _create {} {
-	global repo_config current_branch
+	global repo_config
 	global M1B
 
 	set spec [$w_rev get_tracking_branch]
@@ -155,17 +155,6 @@ method _create {} {
 		return
 	}
 
-	if {$newbranch eq $current_branch} {
-		tk_messageBox \
-			-icon error \
-			-type ok \
-			-title [wm title $w] \
-			-parent $w \
-			-message "'$newbranch' already exists and is the current branch."
-		focus $w_name
-		return
-	}
-
 	if {[catch {git check-ref-format "heads/$newbranch"}]} {
 		tk_messageBox \
 			-icon error \
@@ -178,228 +167,28 @@ method _create {} {
 	}
 
 	if {$spec ne {} && $opt_fetch} {
-		set l_trck [lindex $spec 0]
-		set remote [lindex $spec 1]
-		set r_head [lindex $spec 2]
-		regsub ^refs/heads/ $r_head {} r_head
-
-		set c $w.fetch_trck
-		toplevel $c
-		wm title $c "Refreshing Tracking Branch"
-		wm geometry $c "+[winfo rootx $w]+[winfo rooty $w]"
-
-		set e [::console::embed \
-			$c.console \
-			"Fetching $r_head from $remote"]
-		pack $c.console -fill both -expand 1
-		$e exec \
-			[list git fetch $remote +$r_head:$l_trck] \
-			[cb _finish_fetch $newbranch $c $e]
-
-		bind $c <Visibility> [list grab $c]
-		bind $c <$M1B-Key-w> break
-		bind $c <$M1B-Key-W> break
-		wm protocol $c WM_DELETE_WINDOW [cb _noop]
-	} else {
-		_finish_create $this $newbranch
-	}
-}
-
-method _noop {} {}
-
-method _finish_fetch {newbranch c e ok} {
-	wm protocol $c WM_DELETE_WINDOW {}
-
-	if {$ok} {
-		destroy $c
-		_finish_create $this $newbranch
-	} else {
-		$e done $ok
-		button $c.close -text Close -command [list destroy $c]
-		pack $c.close -side bottom -anchor e -padx 10 -pady 10
-	}
-}
-
-method _finish_create {newbranch} {
-	global null_sha1 all_heads
-
-	if {[catch {set new [$w_rev commit_or_die]}]} {
+		set new {}
+	} elseif {[catch {set new [$w_rev commit_or_die]}]} {
 		return
 	}
 
-	set ref refs/heads/$newbranch
-	if {[catch {set cur [git rev-parse --verify "$ref^0"]}]} {
-		# Assume it does not exist, and that is what the error was.
-		#
-		set reflog_msg "branch: Created from [$w_rev get]"
-		set cur $null_sha1
-	} elseif {$opt_merge eq {no}} {
-		tk_messageBox \
-			-icon error \
-			-type ok \
-			-title [wm title $w] \
-			-parent $w \
-			-message "Branch '$newbranch' already exists."
-		focus $w_name
-		return
-	} else {
-		set mrb {}
-		catch {set mrb [git merge-base $new $cur]}
-		switch -- $opt_merge {
-		ff {
-			if {$mrb eq $new} {
-				# The current branch is actually newer.
-				#
-				set new $cur
-			} elseif {$mrb eq $cur} {
-				# The current branch is older.
-				#
-				set reflog_msg "merge [$w_rev get]: Fast-forward"
-			} else {
-				tk_messageBox \
-					-icon error \
-					-type ok \
-					-title [wm title $w] \
-					-parent $w \
-					-message "Branch '$newbranch' already exists.\n\nIt cannot fast-forward to [$w_rev get].\nA merge is required."
-				focus $w_name
-				return
-			}
-		}
-		reset {
-			if {$mrb eq $cur} {
-				# The current branch is older.
-				#
-				set reflog_msg "merge [$w_rev get]: Fast-forward"
-			} else {
-				# The current branch will lose things.
-				#
-				if {[_confirm_reset $this $newbranch $cur $new]} {
-					set reflog_msg "reset [$w_rev get]"
-				} else {
-					return
-				}
-			}
-		}
-		default {
-			tk_messageBox \
-				-icon error \
-				-type ok \
-				-title [wm title $w] \
-				-parent $w \
-				-message "Branch '$newbranch' already exists."
-			focus $w_name
-			return
-		}
-		}
-	}
-
-	if {$new ne $cur} {
-		if {[catch {
-				git update-ref -m $reflog_msg $ref $new $cur
-			} err]} {
-			tk_messageBox \
-				-icon error \
-				-type ok \
-				-title [wm title $w] \
-				-parent $w \
-				-message "Failed to create '$newbranch'.\n\n$err"
-			return
-		}
-	}
-
-	if {$cur eq $null_sha1} {
-		lappend all_heads $newbranch
-		set all_heads [lsort -uniq $all_heads]
-		populate_branch_menu
-	}
-
-	destroy $w
-	if {$opt_checkout} {
-		switch_branch $newbranch
+	set co [::checkout_op::new \
+		[$w_rev get] \
+		$new \
+		refs/heads/$newbranch]
+	$co parent $w
+	$co enable_create   1
+	$co enable_merge    $opt_merge
+	$co enable_checkout $opt_checkout
+	if {$spec ne {} && $opt_fetch} {
+		$co enable_fetch $spec
 	}
-}
-
-method _confirm_reset {newbranch cur new} {
-	set reset_ok 0
-	set gitk [list do_gitk [list $cur ^$new]]
-
-	set c $w.confirm_reset
-	toplevel $c
-	wm title $c "Confirm Branch Reset"
-	wm geometry $c "+[winfo rootx $w]+[winfo rooty $w]"
 
-	pack [label $c.msg1 \
-		-anchor w \
-		-justify left \
-		-text "Resetting '$newbranch' to [$w_rev get] will lose the following commits:" \
-		] -anchor w
-
-	set list $c.list.l
-	frame $c.list
-	text $list \
-		-font font_diff \
-		-width 80 \
-		-height 10 \
-		-wrap none \
-		-xscrollcommand [list $c.list.sbx set] \
-		-yscrollcommand [list $c.list.sby set]
-	scrollbar $c.list.sbx -orient h -command [list $list xview]
-	scrollbar $c.list.sby -orient v -command [list $list yview]
-	pack $c.list.sbx -fill x -side bottom
-	pack $c.list.sby -fill y -side right
-	pack $list -fill both -expand 1
-	pack $c.list -fill both -expand 1 -padx 5 -pady 5
-
-	pack [label $c.msg2 \
-		-anchor w \
-		-justify left \
-		-text "Recovering lost commits may not be easy." \
-		]
-	pack [label $c.msg3 \
-		-anchor w \
-		-justify left \
-		-text "Reset '$newbranch'?" \
-		]
-
-	frame $c.buttons
-	button $c.buttons.visualize \
-		-text Visualize \
-		-command $gitk
-	pack $c.buttons.visualize -side left
-	button $c.buttons.reset \
-		-text Reset \
-		-command "
-			set @reset_ok 1
-			destroy $c
-		"
-	pack $c.buttons.reset -side right
-	button $c.buttons.cancel \
-		-default active \
-		-text Cancel \
-		-command [list destroy $c]
-	pack $c.buttons.cancel -side right -padx 5
-	pack $c.buttons -side bottom -fill x -pady 10 -padx 10
-
-	set fd [open "| git rev-list --pretty=oneline $cur ^$new" r]
-	while {[gets $fd line] > 0} {
-		set abbr [string range $line 0 7]
-		set subj [string range $line 41 end]
-		$list insert end "$abbr  $subj\n"
+	if {[$co run]} {
+		destroy $w
+	} else {
+		focus $w_name
 	}
-	close $fd
-	$list configure -state disabled
-
-	bind $c    <Key-v> $gitk
-
-	bind $c <Visibility> "
-		grab $c
-		focus $c.buttons.cancel
-	"
-	bind $c <Key-Return> [list destroy $c]
-	bind $c <Key-Escape> [list destroy $c]
-	tkwait window $c
-	return $reset_ok
 }
 
 method _validate {d S} {
diff --git a/lib/branch_delete.tcl b/lib/branch_delete.tcl
index 138e84192c..c7573c6c72 100644
--- a/lib/branch_delete.tcl
+++ b/lib/branch_delete.tcl
@@ -9,7 +9,7 @@ field w_check         ; # revision picker for merge test
 field w_delete        ; # delete button
 
 constructor dialog {} {
-	global all_heads current_branch
+	global current_branch
 
 	make_toplevel top w
 	wm title $top "[appname] ([reponame]): Delete Branch"
@@ -54,7 +54,7 @@ constructor dialog {} {
 	$w_check none {Always (Do not perform merge test.)}
 	pack $w.check -anchor nw -fill x -pady 5 -padx 5
 
-	foreach h $all_heads {
+	foreach h [load_all_heads] {
 		if {$h ne $current_branch} {
 			$w_heads insert end $h
 		}
@@ -79,8 +79,6 @@ method _select {} {
 }
 
 method _delete {} {
-	global all_heads
-
 	if {[catch {set check_cmt [$w_check commit_or_die]}]} {
 		return
 	}
@@ -133,11 +131,6 @@ Delete the selected branches?}
 		set o [lindex $i 1]
 		if {[catch {git update-ref -d "refs/heads/$b" $o} err]} {
 			append failed " - $b: $err\n"
-		} else {
-			set x [lsearch -sorted -exact $all_heads $b]
-			if {$x >= 0} {
-				set all_heads [lreplace $all_heads $x $x]
-			}
 		}
 	}
 
@@ -150,8 +143,6 @@ Delete the selected branches?}
 			-message "Failed to delete branches:\n$failed"
 	}
 
-	set all_heads [lsort $all_heads]
-	populate_branch_menu
 	destroy $w
 }
 
diff --git a/lib/branch_rename.tcl b/lib/branch_rename.tcl
index 405101637f..1cadc31d20 100644
--- a/lib/branch_rename.tcl
+++ b/lib/branch_rename.tcl
@@ -8,7 +8,7 @@ field oldname
 field newname
 
 constructor dialog {} {
-	global all_heads current_branch
+	global current_branch
 
 	make_toplevel top w
 	wm title $top "[appname] ([reponame]): Rename Branch"
@@ -34,7 +34,7 @@ constructor dialog {} {
 
 	frame $w.rename
 	label $w.rename.oldname_l -text {Branch:}
-	eval tk_optionMenu $w.rename.oldname_m @oldname $all_heads
+	eval tk_optionMenu $w.rename.oldname_m @oldname [load_all_heads]
 
 	label $w.rename.newname_l -text {New Name:}
 	entry $w.rename.newname_t \
@@ -64,7 +64,7 @@ constructor dialog {} {
 }
 
 method _rename {} {
-	global all_heads current_branch
+	global current_branch
 
 	if {$oldname eq {}} {
 		tk_messageBox \
@@ -118,14 +118,6 @@ method _rename {} {
 		return
 	}
 
-	set oldidx [lsearch -exact -sorted $all_heads $oldname]
-	if {$oldidx >= 0} {
-		set all_heads [lreplace $all_heads $oldidx $oldidx]
-	}
-	lappend all_heads $newname
-	set all_heads [lsort $all_heads]
-	populate_branch_menu
-
 	if {$current_branch eq $oldname} {
 		set current_branch $newname
 	}
diff --git a/lib/checkout_op.tcl b/lib/checkout_op.tcl
new file mode 100644
index 0000000000..844d8e551c
--- /dev/null
+++ b/lib/checkout_op.tcl
@@ -0,0 +1,569 @@
+# git-gui commit checkout support
+# Copyright (C) 2007 Shawn Pearce
+
+class checkout_op {
+
+field w        {}; # our window (if we have one)
+field w_cons   {}; # embedded console window object
+
+field new_expr   ; # expression the user saw/thinks this is
+field new_hash   ; # commit SHA-1 we are switching to
+field new_ref    ; # ref we are updating/creating
+
+field parent_w      .; # window that started us
+field merge_type none; # type of merge to apply to existing branch
+field fetch_spec   {}; # refetch tracking branch if used?
+field checkout      1; # actually checkout the branch?
+field create        0; # create the branch if it doesn't exist?
+
+field reset_ok      0; # did the user agree to reset?
+field fetch_ok      0; # did the fetch succeed?
+
+field update_old   {}; # was the update-ref call deferred?
+field reflog_msg   {}; # log message for the update-ref call
+
+constructor new {expr hash {ref {}}} {
+	set new_expr $expr
+	set new_hash $hash
+	set new_ref  $ref
+
+	return $this
+}
+
+method parent {path} {
+	set parent_w [winfo toplevel $path]
+}
+
+method enable_merge {type} {
+	set merge_type $type
+}
+
+method enable_fetch {spec} {
+	set fetch_spec $spec
+}
+
+method enable_checkout {co} {
+	set checkout $co
+}
+
+method enable_create {co} {
+	set create $co
+}
+
+method run {} {
+	if {$fetch_spec ne {}} {
+		global M1B
+
+		# We were asked to refresh a single tracking branch
+		# before we get to work.  We should do that before we
+		# consider any ref updating.
+		#
+		set fetch_ok 0
+		set l_trck [lindex $fetch_spec 0]
+		set remote [lindex $fetch_spec 1]
+		set r_head [lindex $fetch_spec 2]
+		regsub ^refs/heads/ $r_head {} r_name
+
+		_toplevel $this {Refreshing Tracking Branch}
+		set w_cons [::console::embed \
+			$w.console \
+			"Fetching $r_name from $remote"]
+		pack $w.console -fill both -expand 1
+		$w_cons exec \
+			[list git fetch $remote +$r_head:$l_trck] \
+			[cb _finish_fetch]
+
+		bind $w <$M1B-Key-w> break
+		bind $w <$M1B-Key-W> break
+		bind $w <Visibility> "
+			[list grab $w]
+			[list focus $w]
+		"
+		wm protocol $w WM_DELETE_WINDOW [cb _noop]
+		tkwait window $w
+
+		if {!$fetch_ok} {
+			delete_this
+			return 0
+		}
+	}
+
+	if {$new_ref ne {}} {
+		# If we have a ref we need to update it before we can
+		# proceed with a checkout (if one was enabled).
+		#
+		if {![_update_ref $this]} {
+			delete_this
+			return 0
+		}
+	}
+
+	if {$checkout} {
+		_checkout $this
+		return 1
+	}
+
+	delete_this
+	return 1
+}
+
+method _noop {} {}
+
+method _finish_fetch {ok} {
+	if {$ok} {
+		set l_trck [lindex $fetch_spec 0]
+		if {[catch {set new_hash [git rev-parse --verify "$l_trck^0"]} err]} {
+			set ok 0
+			$w_cons insert "fatal: Cannot resolve $l_trck"
+			$w_cons insert $err
+		}
+	}
+
+	$w_cons done $ok
+	set w_cons {}
+	wm protocol $w WM_DELETE_WINDOW {}
+
+	if {$ok} {
+		destroy $w
+		set w {}
+	} else {
+		button $w.close -text Close -command [list destroy $w]
+		pack $w.close -side bottom -anchor e -padx 10 -pady 10
+	}
+
+	set fetch_ok $ok
+}
+
+method _update_ref {} {
+	global null_sha1 current_branch
+
+	set ref $new_ref
+	set new $new_hash
+
+	set is_current 0
+	set rh refs/heads/
+	set rn [string length $rh]
+	if {[string equal -length $rn $rh $ref]} {
+		set newbranch [string range $ref $rn end]
+		if {$current_branch eq $newbranch} {
+			set is_current 1
+		}
+	} else {
+		set newbranch $ref
+	}
+
+	if {[catch {set cur [git rev-parse --verify "$ref^0"]}]} {
+		# Assume it does not exist, and that is what the error was.
+		#
+		if {!$create} {
+			_error $this "Branch '$newbranch' does not exist."
+			return 0
+		}
+
+		set reflog_msg "branch: Created from $new_expr"
+		set cur $null_sha1
+	} elseif {$create && $merge_type eq {none}} {
+		# We were told to create it, but not do a merge.
+		# Bad.  Name shouldn't have existed.
+		#
+		_error $this "Branch '$newbranch' already exists."
+		return 0
+	} elseif {!$create && $merge_type eq {none}} {
+		# We aren't creating, it exists and we don't merge.
+		# We are probably just a simple branch switch.
+		# Use whatever value we just read.
+		#
+		set new      $cur
+		set new_hash $cur
+	} elseif {$new eq $cur} {
+		# No merge would be required, don't compute anything.
+		#
+	} else {
+		set mrb {}
+		catch {set mrb [git merge-base $new $cur]}
+		switch -- $merge_type {
+		ff {
+			if {$mrb eq $new} {
+				# The current branch is actually newer.
+				#
+				set new $cur
+			} elseif {$mrb eq $cur} {
+				# The current branch is older.
+				#
+				set reflog_msg "merge $new_expr: Fast-forward"
+			} else {
+				_error $this "Branch '$newbranch' already exists.\n\nIt cannot fast-forward to $new_expr.\nA merge is required."
+				return 0
+			}
+		}
+		reset {
+			if {$mrb eq $cur} {
+				# The current branch is older.
+				#
+				set reflog_msg "merge $new_expr: Fast-forward"
+			} else {
+				# The current branch will lose things.
+				#
+				if {[_confirm_reset $this $cur]} {
+					set reflog_msg "reset $new_expr"
+				} else {
+					return 0
+				}
+			}
+		}
+		default {
+			_error $this "Only 'ff' and 'reset' merge is currently supported."
+			return 0
+		}
+		}
+	}
+
+	if {$new ne $cur} {
+		if {$is_current} {
+			# No so fast.  We should defer this in case
+			# we cannot update the working directory.
+			#
+			set update_old $cur
+			return 1
+		}
+
+		if {[catch {
+				git update-ref -m $reflog_msg $ref $new $cur
+			} err]} {
+			_error $this "Failed to update '$newbranch'.\n\n$err"
+			return 0
+		}
+	}
+
+	return 1
+}
+
+method _checkout {} {
+	if {[lock_index checkout_op]} {
+		after idle [cb _start_checkout]
+	} else {
+		_error $this "Index is already locked."
+		delete_this
+	}
+}
+
+method _start_checkout {} {
+	global HEAD commit_type
+
+	# -- Our in memory state should match the repository.
+	#
+	repository_state curType curHEAD curMERGE_HEAD
+	if {[string match amend* $commit_type]
+		&& $curType eq {normal}
+		&& $curHEAD eq $HEAD} {
+	} elseif {$commit_type ne $curType || $HEAD ne $curHEAD} {
+		info_popup {Last scanned state does not match repository state.
+
+Another Git program has modified this repository since the last scan.  A rescan must be performed before the current branch can be changed.
+
+The rescan will be automatically started now.
+}
+		unlock_index
+		rescan ui_ready
+		delete_this
+		return
+	}
+
+	if {[is_config_true gui.trustmtime]} {
+		_readtree $this
+	} else {
+		ui_status {Refreshing file status...}
+		set cmd [list git update-index]
+		lappend cmd -q
+		lappend cmd --unmerged
+		lappend cmd --ignore-missing
+		lappend cmd --refresh
+		set fd [open "| $cmd" r]
+		fconfigure $fd -blocking 0 -translation binary
+		fileevent $fd readable [cb _refresh_wait $fd]
+	}
+}
+
+method _refresh_wait {fd} {
+	read $fd
+	if {[eof $fd]} {
+		close $fd
+		_readtree $this
+	}
+}
+
+method _name {} {
+	if {$new_ref eq {}} {
+		return [string range $new_hash 0 7]
+	}
+
+	set rh refs/heads/
+	set rn [string length $rh]
+	if {[string equal -length $rn $rh $new_ref]} {
+		return [string range $new_ref $rn end]
+	} else {
+		return $new_ref
+	}
+}
+
+method _readtree {} {
+	global HEAD
+
+	ui_status "Updating working directory to '[_name $this]'..."
+	set cmd [list git read-tree]
+	lappend cmd -m
+	lappend cmd -u
+	lappend cmd --exclude-per-directory=.gitignore
+	lappend cmd $HEAD
+	lappend cmd $new_hash
+	set fd [open "| $cmd" r]
+	fconfigure $fd -blocking 0 -translation binary
+	fileevent $fd readable [cb _readtree_wait $fd]
+}
+
+method _readtree_wait {fd} {
+	global selected_commit_type commit_type HEAD MERGE_HEAD PARENT
+	global current_branch is_detached
+	global ui_comm
+
+	# -- We never get interesting output on stdout; only stderr.
+	#
+	read $fd
+	fconfigure $fd -blocking 1
+	if {![eof $fd]} {
+		fconfigure $fd -blocking 0
+		return
+	}
+
+	set name [_name $this]
+
+	# -- The working directory wasn't in sync with the index and
+	#    we'd have to overwrite something to make the switch. A
+	#    merge is required.
+	#
+	if {[catch {close $fd} err]} {
+		regsub {^fatal: } $err {} err
+		warn_popup "File level merge required.
+
+$err
+
+Staying on branch '$current_branch'."
+		ui_status "Aborted checkout of '$name' (file level merging is required)."
+		unlock_index
+		delete_this
+		return
+	}
+
+	set log "checkout: moving"
+	if {!$is_detached} {
+		append log " from $current_branch"
+	}
+
+	# -- Move/create HEAD as a symbolic ref.  Core git does not
+	#    even check for failure here, it Just Works(tm).  If it
+	#    doesn't we are in some really ugly state that is difficult
+	#    to recover from within git-gui.
+	#
+	set rh refs/heads/
+	set rn [string length $rh]
+	if {[string equal -length $rn $rh $new_ref]} {
+		set new_branch [string range $new_ref $rn end]
+		append log " to $new_branch"
+
+		if {[catch {
+				git symbolic-ref -m $log HEAD $new_ref
+			} err]} {
+			_fatal $this $err
+		}
+		set current_branch $new_branch
+		set is_detached 0
+	} else {
+		append log " to $new_expr"
+
+		if {[catch {
+				_detach_HEAD $log $new_hash
+			} err]} {
+			_fatal $this $err
+		}
+		set current_branch HEAD
+		set is_detached 1
+	}
+
+	# -- We had to defer updating the branch itself until we
+	#    knew the working directory would update.  So now we
+	#    need to finish that work.  If it fails we're in big
+	#    trouble.
+	#
+	if {$update_old ne {}} {
+		if {[catch {
+				git update-ref \
+					-m $reflog_msg \
+					$new_ref \
+					$new_hash \
+					$update_old
+			} err]} {
+			_fatal $this $err
+		}
+	}
+
+	if {$is_detached} {
+		info_popup "You are no longer on a local branch.
+
+If you wanted to be on a branch, create one now starting from 'This Detached Checkout'."
+	}
+
+	# -- Update our repository state.  If we were previously in
+	#    amend mode we need to toss the current buffer and do a
+	#    full rescan to update our file lists.  If we weren't in
+	#    amend mode our file lists are accurate and we can avoid
+	#    the rescan.
+	#
+	unlock_index
+	set selected_commit_type new
+	if {[string match amend* $commit_type]} {
+		$ui_comm delete 0.0 end
+		$ui_comm edit reset
+		$ui_comm edit modified false
+		rescan [list ui_status "Checked out '$name'."]
+	} else {
+		repository_state commit_type HEAD MERGE_HEAD
+		set PARENT $HEAD
+		ui_status "Checked out '$name'."
+	}
+	delete_this
+}
+
+git-version proc _detach_HEAD {log new} {
+	>= 1.5.3 {
+		git update-ref --no-deref -m $log HEAD $new
+	}
+	default {
+		set p [gitdir HEAD]
+		file delete $p
+		set fd [open $p w]
+		fconfigure $fd -translation lf -encoding utf-8
+		puts $fd $new
+		close $fd
+	}
+}
+
+method _confirm_reset {cur} {
+	set reset_ok 0
+	set name [_name $this]
+	set gitk [list do_gitk [list $cur ^$new_hash]]
+
+	_toplevel $this {Confirm Branch Reset}
+	pack [label $w.msg1 \
+		-anchor w \
+		-justify left \
+		-text "Resetting '$name' to $new_expr will lose the following commits:" \
+		] -anchor w
+
+	set list $w.list.l
+	frame $w.list
+	text $list \
+		-font font_diff \
+		-width 80 \
+		-height 10 \