git-gui: Include commit id/subject in merge choices

When merging branches using our local merge feature it can be
handy to know the first few digits of the commit the ref points
at as well as the short description of the branch name.

Unfortunately I'm unable to use three listboxes in a row, as Tcl
freaks out and refuses to let me have a selection in more than
one of them at any given point in time.  So instead we use a
fixed width font in the existing listbox and organize the data
into three columns.  Not nearly as nice looking, but users can
continue to use the listbox's features.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

lib/merge.tcl

@@ -63,28 +63,28 @@ You should complete the current commit before starting a merge.  Doing so will h
 	return 1
 }
 
-proc _visualize {w} {
-	set revs {}
+proc _refs {w list} {
+	set r {}
 	foreach i [$w.source.l curselection] {
-		lappend revs [$w.source.l get $i]
+		lappend r [lindex [lindex $list $i] 0]
 	}
+	return $r
+}
+
+proc _visualize {w list} {
+	set revs [_refs $w $list]
 	if {$revs eq {}} return
 	lappend revs --not HEAD
 	do_gitk $revs
 }
 
-proc _start {w} {
+proc _start {w list} {
 	global HEAD ui_status_value current_branch
 
 	set cmd [list git merge]
-	set names {}
-	set revcnt 0
-	foreach i [$w.source.l curselection] {
-		set b [$w.source.l get $i]
-		lappend cmd $b
-		lappend names $b
-		incr revcnt
-	}
+	set names [_refs $w $list]
+	set revcnt [llength $names]
+	append cmd { } $names
 
 	if {$revcnt == 0} {
 		return
@@ -163,6 +163,36 @@ proc dialog {} {
 
 	if {![_can_merge]} return
 
+	set fmt {list %(objectname) %(*objectname) %(refname) %(subject)}
+	set cmd [list git for-each-ref --tcl --format=$fmt]
+	lappend cmd refs/heads
+	lappend cmd refs/remotes
+	lappend cmd refs/tags
+	set fr_fd [open "| $cmd" r]
+	fconfigure $fr_fd -translation binary
+	while {[gets $fr_fd line] > 0} {
+		set line [eval $line]
+		set ref [lindex $line 2]
+		regsub ^refs/(heads|remotes|tags)/ $ref {} ref
+		set subj($ref) [lindex $line 3]
+		lappend sha1([lindex $line 0]) $ref
+		if {[lindex $line 1] ne {}} {
+			lappend sha1([lindex $line 1]) $ref
+		}
+	}
+	close $fr_fd
+
+	set to_show {}
+	set fr_fd [open "| git rev-list --all --not HEAD"]
+	while {[gets $fr_fd line] > 0} {
+		if {[catch {set ref $sha1($line)}]} continue
+		foreach n $ref {
+			lappend to_show [list $n $line]
+		}
+	}
+	close $fr_fd
+	set to_show [lsort -unique $to_show]
+
 	set w .merge_setup
 	toplevel $w
 	wm geometry $w "+[winfo rootx .]+[winfo rooty .]"
@@ -174,10 +204,10 @@ proc dialog {} {
 
 	frame $w.buttons
 	button $w.buttons.visualize -text Visualize \
-		-command [namespace code [list _visualize $w]]
+		-command [namespace code [list _visualize $w $to_show]]
 	pack $w.buttons.visualize -side left
 	button $w.buttons.create -text Merge \
-		-command [namespace code [list _start $w]]
+		-command [namespace code [list _start $w $to_show]]
 	pack $w.buttons.create -side right
 	button $w.buttons.cancel -text {Cancel} \
 		-command [list destroy $w]
@@ -188,6 +218,7 @@ proc dialog {} {
 	listbox $w.source.l \
 		-height 10 \
 		-width 70 \
+		-font font_diff \
 		-selectmode extended \
 		-yscrollcommand [list $w.source.sby set]
 	scrollbar $w.source.sby -command [list $w.source.l yview]
@@ -195,40 +226,18 @@ proc dialog {} {
 	pack $w.source.l -side left -fill both -expand 1
 	pack $w.source -fill both -expand 1 -pady 5 -padx 5
 
-	set fmt {list %(objectname) %(*objectname) %(refname) %(subject)}
-	set cmd [list git for-each-ref --tcl --format=$fmt]
-	lappend cmd refs/heads
-	lappend cmd refs/remotes
-	lappend cmd refs/tags
-	set fr_fd [open "| $cmd" r]
-	fconfigure $fr_fd -translation binary
-	while {[gets $fr_fd line] > 0} {
-		set line [eval $line]
-		set ref [lindex $line 2]
-		regsub ^refs/(heads|remotes|tags)/ $ref {} ref
-		set subj($ref) [lindex $line 3]
-		lappend sha1([lindex $line 0]) $ref
-		if {[lindex $line 1] ne {}} {
-			lappend sha1([lindex $line 1]) $ref
-		}
-	}
-	close $fr_fd
-
-	set to_show {}
-	set fr_fd [open "| git rev-list --all --not HEAD"]
-	while {[gets $fr_fd line] > 0} {
-		if {[catch {set ref $sha1($line)}]} continue
-		foreach n $ref {
-			lappend to_show $n
+	foreach ref $to_show {
+		set n [lindex $ref 0]
+		if {[string length $n] > 20} {
+			set n "[string range $n 0 16]..."
 		}
-	}
-	close $fr_fd
-
-	foreach ref [lsort -unique $to_show] {
-		$w.source.l insert end $ref
+		$w.source.l insert end [format {%s %-20s %s} \
+			[string range [lindex $ref 1] 0 5] \
+			$n \
+			$subj([lindex $ref 0])]
 	}
 
-	bind $w <Visibility> "grab $w"
+	bind $w <Visibility> "grab $w; focus $w.source.l"
 	bind $w <Key-Escape> "unlock_index;destroy $w"
 	bind $w <Destroy> unlock_index
 	wm title $w "[appname] ([reponame]): Merge"