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>

1 files changed, 36 insertions, 7 deletions

diff --git a/lib/choose_rev.tcl b/lib/choose_rev.tcl
index e6af073595..7f2b4e603d 100644
--- a/lib/choose_rev.tcl
+++ b/lib/choose_rev.tcl
@@ -18,7 +18,7 @@ field spec_trck       ; # list of all tracking branch specs
 field spec_tag        ; # list of all tag specs
 
 constructor new {path {title {}}} {
-	global all_heads current_branch
+	global current_branch is_detached
 
 	set w $path
 
@@ -29,6 +29,15 @@ constructor new {path {title {}}} {
 	}
 	bind $w <Destroy> [cb _delete %W]
 
+	if {$is_detached} {
+		radiobutton $w.detachedhead_r \
+			-anchor w \
+			-text {This Detached Checkout} \
+			-value HEAD \
+			-variable @revtype
+		grid $w.detachedhead_r -sticky we -padx {0 5} -columnspan 2
+	}
+
 	radiobutton $w.expr_r \
 		-text {Revision Expression:} \
 		-value expr \
@@ -86,14 +95,18 @@ constructor new {path {title {}}} {
 	grid $w.list -sticky nswe -padx {20 5} -columnspan 2
 
 	grid columnconfigure $w 1 -weight 1
-	grid rowconfigure    $w 2 -weight 1
+	if {$is_detached} {
+		grid rowconfigure $w 3 -weight 1
+	} else {
+		grid rowconfigure $w 2 -weight 1
+	}
 
 	trace add variable @revtype write [cb _select]
 	bind $w_filter <Key-Return> [list focus $w_list]\;break
 	bind $w_filter <Key-Down>   [list focus $w_list]
 
 	set spec_head [list]
-	foreach name $all_heads {
+	foreach name [load_all_heads] {
 		lappend spec_head [list $name refs/heads/$name]
 	}
 
@@ -109,7 +122,8 @@ constructor new {path {title {}}} {
 		lappend spec_tag [list $name refs/tags/$name]
 	}
 
-	      if {[llength $spec_head] > 0} { set revtype head
+		  if {$is_detached}             { set revtype HEAD
+	} elseif {[llength $spec_head] > 0} { set revtype head
 	} elseif {[llength $spec_trck] > 0} { set revtype trck
 	} elseif {[llength $spec_tag ] > 0} { set revtype tag
 	} else {                              set revtype expr
@@ -153,6 +167,7 @@ method get {} {
 		}
 	}
 
+	HEAD { return HEAD                     }
 	expr { return $c_expr                  }
 	none { return {}                       }
 	default { error "unknown type of revision" }
@@ -163,6 +178,20 @@ method pick_tracking_branch {} {
 	set revtype trck
 }
 
+method focus_filter {} {
+	if {[$w_filter cget -state] eq {normal}} {
+		focus $w_filter
+	}
+}
+
+method get_local_branch {} {
+	if {$revtype eq {head}} {
+		return [_expr $this]
+	} else {
+		return {}
+	}
+}
+
 method get_tracking_branch {} {
 	set i [$w_list curselection]
 	if {$i eq {} || $revtype ne {trck}} {
@@ -222,6 +251,7 @@ method _expr {} {
 			error "Revision expression is empty."
 		}
 	}
+	HEAD { return HEAD                     }
 	none { return {}                       }
 	default { error "unknown type of revision"      }
 	}
@@ -249,9 +279,7 @@ method _filter {P} {
 
 method _select {args} {
 	_rebuild $this $filter
-	if {[$w_filter cget -state] eq {normal}} {
-		focus $w_filter
-	}
+	focus_filter $this
 }
 
 method _rebuild {pat} {
@@ -261,6 +289,7 @@ method _rebuild {pat} {
 	trck { set new $spec_trck }
 	tag  { set new $spec_tag  }
 	expr -
+	HEAD -
 	none {
 		set new [list]
 		set ste disabled