[PATCH v2 3/6] worktree: teach worktree_lock_reason() to gently handle main worktree

[Rafael Silva <rafaeloliveira.cs@gmail.com>]

worktree_lock_reason() aborts with an assertion failure when called on
the main worktree since locking the main worktree is nonsensical. Not
only is this behaviour undocumented, thus callers might not even be aware
that the call could potentially crash the program, but it also forces
clients to be extra careful:

    if (!is_main_worktree(wt) && worktree_locked_reason(...))
        ...

Since we know that locking makes no sense in the context of the main
worktree, we can simpliy return false for the main worktree, thus making
client code less complex by eliminating the need for the callers to have
inside knowledge about the implementation:

    if (worktree_lock_reason(...))
        ...

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Rafael Silva <rafaeloliveira.cs@gmail.com>
---
 worktree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/worktree.c b/worktree.c
index 474ed46562..39495b261b 100644
--- a/worktree.c
+++ b/worktree.c
@@ -225,7 +225,8 @@ int is_main_worktree(const struct worktree *wt)
 
 const char *worktree_lock_reason(struct worktree *wt)
 {
-	assert(!is_main_worktree(wt));
+	if (is_main_worktree(wt))
+		return NULL;
 
 	if (!wt->lock_reason_valid) {
 		struct strbuf path = STRBUF_INIT;
-- 
2.30.0.372.gbc7e965391