From 0d39aa39f3b00992fd0758936c9e42c2228cf1c1 Mon Sep 17 00:00:00 2001
From: Georg Semmler <semmlerg@mailserver.tu-freiberg.de>
Date: Fri, 11 Jun 2021 12:31:50 +0200
Subject: [PATCH] Port the mysql backend to use iterators

---
 diesel/src/mysql/connection/mod.rs           | 45 +++++++++++++-------
 diesel/src/mysql/connection/stmt/iterator.rs |  3 +-
 diesel/src/mysql/connection/stmt/mod.rs      |  8 ++--
 3 files changed, 35 insertions(+), 21 deletions(-)

diff --git a/diesel/src/mysql/connection/mod.rs b/diesel/src/mysql/connection/mod.rs
index e5d4b486d4df..efae0ca6a6bf 100644
--- a/diesel/src/mysql/connection/mod.rs
+++ b/diesel/src/mysql/connection/mod.rs
@@ -20,6 +20,7 @@ pub struct MysqlConnection {
     raw_connection: RawConnection,
     transaction_state: AnsiTransactionManager,
     statement_cache: StatementCache<Mysql, Statement>,
+    current_statement: Option<Statement>,
 }
 
 unsafe impl Send for MysqlConnection {}
@@ -50,6 +51,7 @@ impl Connection for MysqlConnection {
             raw_connection,
             transaction_state: AnsiTransactionManager::default(),
             statement_cache: StatementCache::new(),
+            current_statement: None,
         };
         conn.set_config_options()
             .map_err(CouldntSetupConfiguration)?;
@@ -73,11 +75,22 @@ impl Connection for MysqlConnection {
         T::Query: QueryFragment<Self::Backend> + QueryId,
         Self::Backend: QueryMetadata<T::SqlType>,
     {
-        let mut stmt = self.prepare_query(&source.as_query())?;
-        let mut metadata = Vec::new();
-        Mysql::row_metadata(&mut (), &mut metadata);
-        let results = unsafe { stmt.results(metadata)? };
-        Ok(results)
+        self.with_prepared_query(&source.as_query(), |stmt, current_statement| {
+            let mut metadata = Vec::new();
+            Mysql::row_metadata(&mut (), &mut metadata);
+            let stmt = match stmt {
+                MaybeCached::CannotCache(stmt) => {
+                    *current_statement = Some(stmt);
+                    current_statement
+                        .as_mut()
+                        .expect("We set it literally above")
+                }
+                MaybeCached::Cached(stmt) => stmt,
+            };
+
+            let results = unsafe { stmt.results(metadata)? };
+            Ok(results)
+        })
     }
 
     #[doc(hidden)]
@@ -85,11 +98,12 @@ impl Connection for MysqlConnection {
     where
         T: QueryFragment<Self::Backend> + QueryId,
     {
-        let stmt = self.prepare_query(source)?;
-        unsafe {
-            stmt.execute()?;
-        }
-        Ok(stmt.affected_rows())
+        self.with_prepared_query(source, |stmt, _| {
+            unsafe {
+                stmt.execute()?;
+            }
+            Ok(stmt.affected_rows())
+        })
     }
 
     #[doc(hidden)]
@@ -99,10 +113,11 @@ impl Connection for MysqlConnection {
 }
 
 impl MysqlConnection {
-    fn prepare_query<T>(&mut self, source: &T) -> QueryResult<MaybeCached<Statement>>
-    where
-        T: QueryFragment<Mysql> + QueryId,
-    {
+    fn with_prepared_query<'a, T: QueryFragment<Mysql> + QueryId, R>(
+        &'a mut self,
+        source: &'_ T,
+        f: impl FnOnce(MaybeCached<'a, Statement>, &'a mut Option<Statement>) -> QueryResult<R>,
+    ) -> QueryResult<R> {
         let cache = &mut self.statement_cache;
         let conn = &mut self.raw_connection;
 
@@ -114,7 +129,7 @@ impl MysqlConnection {
             .into_iter()
             .zip(bind_collector.binds);
         stmt.bind(binds)?;
-        Ok(stmt)
+        f(stmt, &mut self.current_statement)
     }
 
     fn set_config_options(&mut self) -> QueryResult<()> {
diff --git a/diesel/src/mysql/connection/stmt/iterator.rs b/diesel/src/mysql/connection/stmt/iterator.rs
index e6a78e48298b..854e5c86bee7 100644
--- a/diesel/src/mysql/connection/stmt/iterator.rs
+++ b/diesel/src/mysql/connection/stmt/iterator.rs
@@ -2,7 +2,6 @@ use std::marker::PhantomData;
 use std::rc::Rc;
 
 use super::{Binds, Statement, StatementMetadata};
-use super::metadata::MysqlFieldMetadata;
 use crate::mysql::{Mysql, MysqlType};
 use crate::result::QueryResult;
 use crate::row::*;
@@ -152,7 +151,7 @@ pub struct MysqlField<'a> {
     bind: Rc<Binds>,
     metadata: Rc<StatementMetadata>,
     idx: usize,
-    _marker: PhantomData<&'a (Binds, StatementMetadata)>
+    _marker: PhantomData<&'a (Binds, StatementMetadata)>,
 }
 
 impl<'a> Field<Mysql> for MysqlField<'a> {
diff --git a/diesel/src/mysql/connection/stmt/mod.rs b/diesel/src/mysql/connection/stmt/mod.rs
index 31b556bf2bcb..6c828a786d7b 100644
--- a/diesel/src/mysql/connection/stmt/mod.rs
+++ b/diesel/src/mysql/connection/stmt/mod.rs
@@ -9,7 +9,7 @@ use std::os::raw as libc;
 use std::ptr::NonNull;
 
 use self::iterator::*;
-use super::bind::{BindData, Binds};
+use super::bind::Binds;
 use crate::mysql::MysqlType;
 use crate::result::{DatabaseErrorKind, Error, QueryResult};
 
@@ -80,10 +80,10 @@ impl Statement {
     /// This function should be called instead of `execute` for queries which
     /// have a return value. After calling this function, `execute` can never
     /// be called on this statement.
-    pub unsafe fn results(
-        self,
+    pub unsafe fn results<'a>(
+        &'a mut self,
         types: Vec<Option<MysqlType>>,
-    ) -> QueryResult<StatementIterator> {
+    ) -> QueryResult<StatementIterator<'a>> {
         StatementIterator::new(self, types)
     }