[PATCH] git-gui: handle bare repo or missing worktree

[Shroom Moo <egg_mushroomcow@foxmail.com>]

When starting git-gui from a directory that Git recognizes as a valid
repository but the repository is either bare or its working tree is
missing, git-gui previously attempted to execute 'rev-parse
--show-toplevel' without error handling. This caused a fatal Tcl error
("this operation must be run in a work tree") and prevented the user
from opening the repository selection dialog.

Improve the repository setup logic:
- After obtaining the git directory via 'rev-parse --git-dir', check
  whether the repository is bare or if the working tree can be
  successfully located.
- If the repository is unusable as a working tree, display a warning
  and present the "Create/Clone/Open" repository selection dialog.

This makes git-gui robust when launched from a bare repository, from
inside a .git directory without a worktree, or when GIT_DIR points to
an invalid location. No regressions observed in normal working trees.

Signed-off-by: Shroom Moo <egg_mushroomcow@foxmail.com>
---
 git-gui/git-gui.sh | 75 +++++++++++++++++++++++++++++++++++-----------
 1 file changed, 57 insertions(+), 18 deletions(-)

diff --git a/git-gui/git-gui.sh b/git-gui/git-gui.sh
index 23fe76e498..2e4bc2f226 100755
--- a/git-gui/git-gui.sh
+++ b/git-gui/git-gui.sh
@@ -1123,24 +1123,63 @@ unset argv0dir
 ## repository setup
 
 set picked 0
-if {[catch {
-		set _gitdir $env(GIT_DIR)
-		set _prefix {}
-		}]
-	&& [catch {
-		# beware that from the .git dir this sets _gitdir to .
-		# and _prefix to the empty string
-		set _gitdir [git rev-parse --git-dir]
-		set _prefix [git rev-parse --show-prefix]
-	} err]} {
-	load_config 1
-	apply_config
-	choose_repository::pick
-	if {![file isdirectory $_gitdir]} {
-		exit 1
-	}
-	set picked 1
-}
+# Save temporarily for restoration later
+set _startup_cwd [pwd]
+
+set need_pick 0
+if {[catch {set _gitdir $env(GIT_DIR); set _prefix {}}]} {
+    # GIT_DIR not set in environment, attempt auto-detection
+	# beware that from the .git dir this sets _gitdir to .
+	# and _prefix to the empty string
+    if {[catch {set _gitdir [git rev-parse --git-dir]; set _prefix [git rev-parse --show-prefix]} err]} {
+        # Not inside any Git repository, proceed to repository selection UI
+        set need_pick 1
+    } else {
+        # Inside a Git repository, but need to verify its usability
+        cd [file dirname $_gitdir]
+        set bare 0
+        set worktree_missing 0
+		# Check if this is a bare repository (no working tree)
+        if {![catch {set bare [git rev-parse --is-bare-repository]}]} {
+            if {$bare eq "true"} {
+                set bare 1
+            }
+        }
+		# Check if working tree is present and accessible
+        if {[catch {git rev-parse --show-toplevel}]} {
+            set worktree_missing 1
+        }
+
+        cd $_startup_cwd
+
+        # For bare repos or missing worktrees, warn and guide to selection
+        if {$bare || $worktree_missing} {
+            set msg [mc "The repository at '%s' cannot be opened:" [file normalize $_gitdir]]
+            if {$bare} {
+                append msg "\n\n" [mc "It is a bare repository (no working tree)."]
+            } else {
+                append msg "\n\n" [mc "The working tree appears to be missing or inaccessible."]
+            }
+            append msg "\n\n" [mc "Please select a valid working repository, or create/clone one."]
+            tk_messageBox -icon warning -type ok -title [mc "Repository Unusable"] -message $msg
+
+            set need_pick 1
+        }
+    }
+}
+
+if {$need_pick} {
+    load_config 1
+    apply_config
+    choose_repository::pick
+    if {![file isdirectory $_gitdir]} {
+        exit 1
+    }
+    set picked 1
+}
+
+# Clean up working tree checking temporary variables
+unset -nocomplain _startup_cwd need_pick bare worktree_missing
 
 # Use object format as hash algorithm (either "sha1" or "sha256")
 set hashalgorithm [git rev-parse --show-object-format]
-- 
2.52.0.windows.1