remove depth from Savepoint

Savepoints with the same name nest properly without issue.  This doesn't
work with rusqlite unless savepoints are always released on drop.

src/transaction.rs

@@ -91,7 +91,6 @@ pub struct Transaction<'conn> {
 pub struct Savepoint<'conn> {
     conn: &'conn Connection,
     name: String,
-    depth: u32,
     drop_behavior: DropBehavior,
     committed: bool,
 }
@@ -158,13 +157,13 @@ impl Transaction<'_> {
     /// ```
     #[inline]
     pub fn savepoint(&mut self) -> Result<Savepoint<'_>> {
-        Savepoint::with_depth(self.conn, 1)
+        Savepoint::new_(self.conn)
     }
 
     /// Create a new savepoint with a custom savepoint name. See `savepoint()`.
     #[inline]
     pub fn savepoint_with_name<T: Into<String>>(&mut self, name: T) -> Result<Savepoint<'_>> {
-        Savepoint::with_depth_and_name(self.conn, 1, name)
+        Savepoint::with_name_(self.conn, name)
     }
 
     /// Get the current setting for what happens to the transaction when it is
@@ -249,50 +248,44 @@ impl Drop for Transaction<'_> {
 
 impl Savepoint<'_> {
     #[inline]
-    fn with_depth_and_name<T: Into<String>>(
-        conn: &Connection,
-        depth: u32,
-        name: T,
-    ) -> Result<Savepoint<'_>> {
+    fn with_name_<T: Into<String>>(conn: &Connection, name: T) -> Result<Savepoint<'_>> {
         let name = name.into();
         conn.execute_batch(&format!("SAVEPOINT {name}"))
             .map(|_| Savepoint {
                 conn,
                 name,
-                depth,
                 drop_behavior: DropBehavior::Rollback,
                 committed: false,
             })
     }
 
     #[inline]
-    fn with_depth(conn: &Connection, depth: u32) -> Result<Savepoint<'_>> {
-        let name = format!("_rusqlite_sp_{depth}");
-        Savepoint::with_depth_and_name(conn, depth, name)
+    fn new_(conn: &Connection) -> Result<Savepoint<'_>> {
+        Savepoint::with_name_(conn, "_rusqlite_sp")
     }
 
     /// Begin a new savepoint. Can be nested.
     #[inline]
     pub fn new(conn: &mut Connection) -> Result<Savepoint<'_>> {
-        Savepoint::with_depth(conn, 0)
+        Savepoint::new_(conn)
     }
 
     /// Begin a new savepoint with a user-provided savepoint name.
     #[inline]
     pub fn with_name<T: Into<String>>(conn: &mut Connection, name: T) -> Result<Savepoint<'_>> {
-        Savepoint::with_depth_and_name(conn, 0, name)
+        Savepoint::with_name_(conn, name)
     }
 
     /// Begin a nested savepoint.
     #[inline]
     pub fn savepoint(&mut self) -> Result<Savepoint<'_>> {
-        Savepoint::with_depth(self.conn, self.depth + 1)
+        Savepoint::new_(self.conn)
     }
 
     /// Begin a nested savepoint with a user-provided savepoint name.
     #[inline]
     pub fn savepoint_with_name<T: Into<String>>(&mut self, name: T) -> Result<Savepoint<'_>> {
-        Savepoint::with_depth_and_name(self.conn, self.depth + 1, name)
+        Savepoint::with_name_(self.conn, name)
     }
 
     /// Get the current setting for what happens to the savepoint when it is
@@ -352,7 +345,7 @@ impl Savepoint<'_> {
         }
         match self.drop_behavior() {
             DropBehavior::Commit => self.commit_().or_else(|_| self.rollback()),
-            DropBehavior::Rollback => self.rollback(),
+            DropBehavior::Rollback => self.rollback().and_then(|_| self.commit_()),
             DropBehavior::Ignore => Ok(()),
             DropBehavior::Panic => panic!("Savepoint dropped unexpectedly."),
         }