git-gui: handle bare repos correctly

Refactor checking for a bare repository into its own proc, that relies
on git rev-parse --is-bare-repository if possible. For older versions of
git we fall back to a logic such that the repository is considered bare
if:
 * either the core.bare setting is true
 * or the worktree is not set and the directory name ends with .git
The error message for the case of an unhandled bare repository is also
updated to reflect the fact that the problem is not the funny name but
the bareness.

The new refactored proc is also used to disable the menu entry to
explore the working copy, and to skip changing to the worktree before
the gitk invocation.

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -122,6 +122,7 @@ unset oguimsg
 set _appname {Git Gui}
 set _gitdir {}
 set _gitworktree {}
+set _isbare {}
 set _gitexec {}
 set _githtmldir {}
 set _reponame {}
@@ -277,6 +278,32 @@ proc get_config {name} {
 	}
 }
 
+proc is_bare {} {
+	global _isbare
+	global _gitdir
+	global _gitworktree
+
+	if {$_isbare eq {}} {
+		if {[catch {
+			set _bare [git rev-parse --is-bare-repository]
+			switch  -- $_bare {
+			true { set _isbare 1 }
+			false { set _isbare 0}
+			default { throw }
+			}
+		}]} {
+			if {[is_config_true core.bare]
+				|| ($_gitworktree eq {}
+					&& [lindex [file split $_gitdir] end] ne {.git})} {
+				set _isbare 1
+			} else {
+				set _isbare 0
+			}
+		}
+	}
+	return $_isbare
+}
+
 ######################################################################
 ##
 ## handy utils
@@ -1122,9 +1149,9 @@ if {$_prefix ne {}} {
 	set _gitworktree [pwd]
 	unset cdup
 } elseif {![is_enabled bare]} {
-	if {[lindex [file split $_gitdir] end] ne {.git}} {
+	if {[is_bare]} {
 		catch {wm withdraw .}
-		error_popup [strcat [mc "Cannot use funny .git directory:"] "\n\n$_gitdir"]
+		error_popup [strcat [mc "Cannot use bare repository:"] "\n\n$_gitdir"]
 		exit 1
 	}
 	if {$_gitworktree eq {}} {
@@ -1973,7 +2000,7 @@ proc do_gitk {revs {is_submodule false}} {
 		set pwd [pwd]
 
 		if {!$is_submodule} {
-			if {$_gitworktree ne {}} {
+			if {![is_bare]} {
 				cd $_gitworktree
 			}
 			set env(GIT_DIR) [file normalize [gitdir]]
@@ -2457,10 +2484,12 @@ if {[is_enabled multicommit] || [is_enabled singlecommit]} {
 #
 menu .mbar.repository
 
-.mbar.repository add command \
-	-label [mc "Explore Working Copy"] \
-	-command {do_explore}
-.mbar.repository add separator
+if {![is_bare]} {
+	.mbar.repository add command \
+		-label [mc "Explore Working Copy"] \
+		-command {do_explore}
+	.mbar.repository add separator
+}
 
 .mbar.repository add command \
 	-label [mc "Browse Current Branch's Files"] \