git-gui: Allow users to match remote branch names locally

Some workflows have users create a local branch that matches a remote
branch they have fetched from another repository.  If the user wants
to push their changes back to that remote repository then they probably
want to use the same branch name locally so that git-gui's push dialog
can setup the push refspec automatically.

To prevent typos with the local branch name we now offer an option to
use the remote tracking branch name as the new local branch name.

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

lib/branch_create.tcl

@@ -8,6 +8,8 @@ field w_rev          ; # mega-widget to pick the initial revision
 field w_name         ; # new branch name widget
 
 field name         {}; # name of the branch the user has chosen
+field name_type  user; # type of branch name to use
+
 field opt_checkout  1; # automatically checkout the new branch?
 
 constructor dialog {} {
@@ -32,10 +34,12 @@ constructor dialog {} {
 	pack $w.buttons.cancel -side right -padx 5
 	pack $w.buttons -side bottom -fill x -pady 10 -padx 10
 
-	labelframe $w.desc -text {Branch Description}
-	label $w.desc.name_r \
+	labelframe $w.desc -text {Branch Name}
+	radiobutton $w.desc.name_r \
 		-anchor w \
-		-text {Name:}
+		-text {Name:} \
+		-value user \
+		-variable @name_type
 	set w_name $w.desc.name_t
 	entry $w_name \
 		-borderwidth 1 \
@@ -46,6 +50,13 @@ constructor dialog {} {
 		-validatecommand [cb _validate %d %S]
 	grid $w.desc.name_r $w_name -sticky we -padx {0 5}
 
+	radiobutton $w.desc.match_r \
+		-anchor w \
+		-text {Match Tracking Branch Name} \
+		-value match \
+		-variable @name_type
+	grid $w.desc.match_r -sticky we -padx {0 5} -columnspan 2
+
 	grid columnconfigure $w.desc 1 -weight 1
 	pack $w.desc -anchor nw -fill x -pady 5 -padx 5
 
@@ -75,7 +86,33 @@ method _create {} {
 	global null_sha1 repo_config
 	global all_heads
 
-	set newbranch $name
+	switch -- $name_type {
+	user {
+		set newbranch $name
+	}
+	match {
+		set spec [$w_rev get_tracking_branch]
+		if {$spec eq {}} {
+			tk_messageBox \
+				-icon error \
+				-type ok \
+				-title [wm title $w] \
+				-parent $w \
+				-message "Please select a tracking branch."
+			return
+		}
+		if {![regsub ^refs/heads/ [lindex $spec 2] {} newbranch]} {
+			tk_messageBox \
+				-icon error \
+				-type ok \
+				-title [wm title $w] \
+				-parent $w \
+				-message "Tracking branch [$w get] is not a branch in the remote repository."
+			return
+		}
+	}
+	}
+
 	if {$newbranch eq {}
 		|| $newbranch eq $repo_config(gui.newbranchtemplate)} {
 		tk_messageBox \

lib/choose_rev.tcl

@@ -128,6 +128,14 @@ method get {} {
 	}
 }
 
+method get_tracking_branch {} {
+	if {$revtype eq {trck}} {
+		return $trck_spec($c_trck)
+	} else {
+		return {}
+	}
+}
+
 method get_expr {} {
 	switch -- $revtype {
 	head { return refs/heads/$c_head             }