git-gui: Internalize symbolic-ref HEAD reading logic

To improve performance on fork+exec impoverished systems (such as
Windows) we want to avoid running git-symbolic-ref on every rescan
if we can do so.  A quick way to implement such an avoidance is to
just read the HEAD ref ourselves; we'll either see it as a symref
(starts with "ref: ") or we'll see it as a detached head (40 hex
digits).  In either case we can treat that as our current branch.

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

diff --git a/git-gui.sh b/git-gui.sh
index 3bd12d20b5f787a2b5119b3a2f1eebbd310a50c1..5dc2c675a92b65598a02a74b4a27ba3db1f4f86f 100755 (executable)
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -262,6 +262,17 @@ proc git {args} {
        return [eval exec git $args]
 }
 
+proc current-branch {} {
+       set ref {}
+       set fd [open [gitdir HEAD] r]
+       if {[gets $fd ref] <16
+        || ![regsub {^ref: refs/heads/} $ref {} ref]} {
+               set ref {}
+       }
+       close $fd
+       return $ref
+}
+
 auto_load tk_optionMenu
 rename tk_optionMenu real__tkOptionMenu
 proc tk_optionMenu {w varName args} {
@@ -410,15 +421,7 @@ proc repository_state {ctvar hdvar mhvar} {
 
        set mh [list]
 
-       if {[catch {set current_branch [git symbolic-ref HEAD]}]} {
-               set current_branch {}
-       } else {
-               regsub ^refs/((heads|tags|remotes)/)? \
-                       $current_branch \
-                       {} \
-                       current_branch
-       }
-
+       set current_branch [current-branch]
        if {[catch {set hd [git rev-parse --verify HEAD]}]} {
                set hd {}
                set ct initial
@@ -1651,14 +1654,8 @@ switch -- $subcommand {
 browser {
        set subcommand_args {rev?}
        switch [llength $argv] {
-       0 {
-               set current_branch [git symbolic-ref HEAD]
-               regsub ^refs/((heads|tags|remotes)/)? \
-                       $current_branch {} current_branch
-       }
-       1 {
-               set current_branch [lindex $argv 0]
-       }
+       0 { set current_branch [current-branch] }
+       1 { set current_branch [lindex $argv 0] }
        default usage
        }
        browser::new $current_branch
@@ -1691,9 +1688,7 @@ blame {
        unset is_path
 
        if {$head eq {}} {
-               set current_branch [git symbolic-ref HEAD]
-               regsub ^refs/((heads|tags|remotes)/)? \
-                       $current_branch {} current_branch
+               set current_branch [current-branch]
        } else {
                set current_branch $head
        }