fix(sqlite): reset the statement when fetch_many() stream is dropped

Unlike `Executor.fetch_optional()`, `Executor.fetch_many()` does not
have a single exit.  The stream can be dropped at any time.  To catch
this event, we create a `StatementResetter` structure inside the stream
loop and reset the statement when it is dropped.

A test case `it_resets_prepared_statement_after_fetch_many` is
similar to `it_resets_prepared_statement_after_fetch_one` which tests
`Executor.fetch_optional()`.

sqlx-core/src/sqlite/connection/executor.rs

@@ -59,6 +59,24 @@ fn bind(
     Ok(n)
 }
 
+/// A structure holding sqlite statement handle and resetting the
+/// statement when it is dropped.
+struct StatementResetter {
+    handle: StatementHandle,
+}
+
+impl StatementResetter {
+    fn new(handle: StatementHandle) -> Self {
+        Self { handle }
+    }
+}
+
+impl Drop for StatementResetter {
+    fn drop(&mut self) {
+        self.handle.reset();
+    }
+}
+
 impl<'c> Executor<'c> for &'c mut SqliteConnection {
     type Database = Sqlite;
 
@@ -91,6 +109,12 @@ impl<'c> Executor<'c> for &'c mut SqliteConnection {
             let mut num_arguments = 0;
 
             while let Some((stmt, columns, column_names, last_row_values)) = stmt.prepare(conn)? {
+                // Prepare to reset raw SQLite statement when the handle
+                // is dropped. `StatementResetter` will reliably reset the
+                // statement even if the stream returned from `fetch_many`
+                // is dropped early.
+                let _resetter = StatementResetter::new(*stmt);
+
                 // bind values to the statement
                 num_arguments += bind(stmt, &arguments, num_arguments)?;
 

sqlx-core/src/sqlite/statement/handle.rs

@@ -13,8 +13,9 @@ use libsqlite3_sys::{
     sqlite3_column_count, sqlite3_column_database_name, sqlite3_column_decltype,
     sqlite3_column_double, sqlite3_column_int, sqlite3_column_int64, sqlite3_column_name,
     sqlite3_column_origin_name, sqlite3_column_table_name, sqlite3_column_type,
-    sqlite3_column_value, sqlite3_db_handle, sqlite3_sql, sqlite3_stmt, sqlite3_stmt_readonly,
-    sqlite3_table_column_metadata, sqlite3_value, SQLITE_OK, SQLITE_TRANSIENT, SQLITE_UTF8,
+    sqlite3_column_value, sqlite3_db_handle, sqlite3_reset, sqlite3_sql, sqlite3_stmt,
+    sqlite3_stmt_readonly, sqlite3_table_column_metadata, sqlite3_value, SQLITE_OK,
+    SQLITE_TRANSIENT, SQLITE_UTF8,
 };
 
 use crate::error::{BoxDynError, Error};
@@ -278,4 +279,8 @@ impl StatementHandle {
     pub(crate) fn column_text(&self, index: usize) -> Result<&str, BoxDynError> {
         Ok(from_utf8(self.column_blob(index))?)
     }
+
+    pub(crate) fn reset(&self) {
+        unsafe { sqlite3_reset(self.0.as_ptr()) };
+    }
 }