gitk: Show branch name(s) as well, if "show nearby tags" is enabled

This is a small extension to the code that reads the complete commit
graph, to make it compute descendent heads as well as descendent tags.
We don't exclude descendent heads that are descendents of other
descendent heads as we do for tags, since it is useful to know all the
branches that a commit is on.
Signed-off-by: NPaul Mackerras <paulus@samba.org>

gitk

@@ -3568,14 +3568,17 @@ proc viewnextline {dir} {
     allcanvs yview moveto [expr {$newtop * 1.0 / $ymax}]
 }
 
-# add a list of tag names at position pos
-proc appendrefs {pos l} {
-    global ctext commitrow linknum curview idtags
+# add a list of tag or branch names at position pos
+# returns the number of names inserted
+proc appendrefs {pos l var} {
+    global ctext commitrow linknum curview idtags $var
 
-    if {[catch {$ctext index $pos}]} return
+    if {[catch {$ctext index $pos}]} {
+	return 0
+    }
     set tags {}
     foreach id $l {
-	foreach tag $idtags($id) {
+	foreach tag [set $var\($id\)] {
 	    lappend tags [concat $tag $id]
 	}
     }
@@ -3598,20 +3601,27 @@ proc appendrefs {pos l} {
 	}
 	set sep ", "
     }
+    return [llength $tags]
 }
 
 # called when we have finished computing the nearby tags
 proc dispneartags {} {
     global selectedline currentid ctext anc_tags desc_tags showneartags
+    global desc_heads
 
     if {![info exists selectedline] || !$showneartags} return
     set id $currentid
     $ctext conf -state normal
+    if {[info exists desc_heads($id)]} {
+	if {[appendrefs branch $desc_heads($id) idheads] > 1} {
+	    $ctext insert "branch -2c" "es"
+	}
+    }
     if {[info exists anc_tags($id)]} {
-	appendrefs follows $anc_tags($id)
+	appendrefs follows $anc_tags($id) idtags
     }
     if {[info exists desc_tags($id)]} {
-	appendrefs precedes $desc_tags($id)
+	appendrefs precedes $desc_tags($id) idtags
     }
     $ctext conf -state disabled
 }
@@ -3623,7 +3633,7 @@ proc selectline {l isnew} {
     global currentid sha1entry
     global commentend idtags linknum
     global mergemax numcommits pending_select
-    global cmitmode desc_tags anc_tags showneartags allcommits
+    global cmitmode desc_tags anc_tags showneartags allcommits desc_heads
 
     catch {unset pending_select}
     $canv delete hover
@@ -3740,17 +3750,26 @@ proc selectline {l isnew} {
 	if {![info exists allcommits]} {
 	    getallcommits
 	}
-	$ctext insert end "Follows: "
+	$ctext insert end "Branch: "
+	$ctext mark set branch "end -1c"
+	$ctext mark gravity branch left
+	if {[info exists desc_heads($id)]} {
+	    if {[appendrefs branch $desc_heads($id) idheads] > 1} {
+		# turn "Branch" into "Branches"
+		$ctext insert "branch -2c" "es"
+	    }
+	}
+	$ctext insert end "\nFollows: "
 	$ctext mark set follows "end -1c"
 	$ctext mark gravity follows left
 	if {[info exists anc_tags($id)]} {
-	    appendrefs follows $anc_tags($id)
+	    appendrefs follows $anc_tags($id) idtags
 	}
 	$ctext insert end "\nPrecedes: "
 	$ctext mark set precedes "end -1c"
 	$ctext mark gravity precedes left
 	if {[info exists desc_tags($id)]} {
-	    appendrefs precedes $desc_tags($id)
+	    appendrefs precedes $desc_tags($id) idtags
 	}
 	$ctext insert end "\n"
     }
@@ -5042,6 +5061,7 @@ proc combine_atags {l1 l2} {
 proc getallclines {fd} {
     global allparents allchildren allcommits allcstart
     global desc_tags anc_tags idtags alldtags tagisdesc allids
+    global desc_heads idheads
 
     while {[gets $fd line] >= 0} {
 	set id [lindex $line 0]
@@ -5055,7 +5075,9 @@ proc getallclines {fd} {
 	    lappend allchildren($p) $id
 	}
 	# compute nearest tagged descendents as we go
+	# also compute descendent heads
 	set dtags {}
+	set dheads {}
 	foreach child $allchildren($id) {
 	    if {[info exists idtags($child)]} {
 		set ctags [list $child]
@@ -5067,6 +5089,12 @@ proc getallclines {fd} {
 	    } elseif {$ctags ne $dtags} {
 		set dtags [combine_dtags $dtags $ctags]
 	    }
+	    set cheads $desc_heads($child)
+	    if {$dheads eq {}} {
+		set dheads $cheads
+	    } elseif {$cheads ne $dheads} {
+		set dheads [lsort -unique [concat $dheads $cheads]]
+	    }
 	}
 	set desc_tags($id) $dtags
 	if {[info exists idtags($id)]} {
@@ -5081,6 +5109,10 @@ proc getallclines {fd} {
 		set tagisdesc($tag,$id) 1
 	    }
 	}
+	if {[info exists idheads($id)]} {
+	    lappend dheads $id
+	}
+	set desc_heads($id) $dheads
 	if {[clock clicks -milliseconds] - $allcstart >= 50} {
 	    fileevent $fd readable {}
 	    after idle restartgetall $fd