add CLIENT_FOUND_ROWS flag to mysql connect

CHANGELOG.md

@@ -182,6 +182,8 @@ for Rust libraries in [RFC #1105](https://github.com/rust-lang/rfcs/blob/master/
 * The sqlite backend now uses a single batch insert statement if there are now default values present 
   in the values clause
 
+* The MySQL connection is using the CLIENT_FOUND_ROWS from now on. This means that updating rows without changing any values will return the number of matched rows (like most other SQL servers do), as opposed to the number of changed rows.
+
 ### Fixed
 
 * Many types were incorrectly considered non-aggregate when they should not

diesel/src/mysql/connection/mod.rs

@@ -166,4 +166,23 @@ mod tests {
         assert!(connection.execute("SELECT 1").is_ok());
         assert!(connection.execute("SELECT 1").is_ok());
     }
+
+    #[test]
+    fn check_client_found_rows_flag() {
+        let conn = &mut crate::test_helpers::connection();
+        conn.execute("DROP TABLE IF EXISTS update_test CASCADE")
+            .unwrap();
+
+        conn.execute("CREATE TABLE update_test(id INTEGER PRIMARY KEY, num INTEGER NOT NULL)")
+            .unwrap();
+
+        conn.execute("INSERT INTO update_test(id, num) VALUES (1, 5)")
+            .unwrap();
+
+        let output = conn
+            .execute("UPDATE update_test SET num = 5 WHERE id = 1")
+            .unwrap();
+
+        assert_eq!(output, 1);
+    }
 }

diesel/src/mysql/connection/raw.rs

@@ -46,6 +46,7 @@ impl RawConnection {
         let database = connection_options.database();
         let port = connection_options.port();
         let unix_socket = connection_options.unix_socket();
+        let client_flags = connection_options.client_flags();
 
         unsafe {
             // Make sure you don't use the fake one!
@@ -63,7 +64,7 @@ impl RawConnection {
                 unix_socket
                     .map(CStr::as_ptr)
                     .unwrap_or_else(|| ptr::null_mut()),
-                0,
+                client_flags.bits().into(),
             )
         };
 

diesel/src/mysql/connection/url.rs

@@ -8,13 +8,44 @@ use std::ffi::{CStr, CString};
 
 use crate::result::{ConnectionError, ConnectionResult};
 
+bitflags::bitflags! {
+    pub struct CapabilityFlags: u32 {
+        const CLIENT_LONG_PASSWORD = 0x00000001;
+        const CLIENT_FOUND_ROWS = 0x00000002;
+        const CLIENT_LONG_FLAG = 0x00000004;
+        const CLIENT_CONNECT_WITH_DB = 0x00000008;
+        const CLIENT_NO_SCHEMA = 0x00000010;
+        const CLIENT_COMPRESS = 0x00000020;
+        const CLIENT_ODBC = 0x00000040;
+        const CLIENT_LOCAL_FILES = 0x00000080;
+        const CLIENT_IGNORE_SPACE = 0x00000100;
+        const CLIENT_PROTOCOL_41 = 0x00000200;
+        const CLIENT_INTERACTIVE = 0x00000400;
+        const CLIENT_SSL = 0x00000800;
+        const CLIENT_IGNORE_SIGPIPE = 0x00001000;
+        const CLIENT_TRANSACTIONS = 0x00002000;
+        const CLIENT_RESERVED = 0x00004000;
+        const CLIENT_SECURE_CONNECTION = 0x00008000;
+        const CLIENT_MULTI_STATEMENTS = 0x00010000;
+        const CLIENT_MULTI_RESULTS = 0x00020000;
+        const CLIENT_PS_MULTI_RESULTS = 0x00040000;
+        const CLIENT_PLUGIN_AUTH = 0x00080000;
+        const CLIENT_CONNECT_ATTRS = 0x00100000;
+        const CLIENT_PLUGIN_AUTH_LENENC_CLIENT_DATA = 0x00200000;
+        const CLIENT_CAN_HANDLE_EXPIRED_PASSWORDS = 0x00400000;
+        const CLIENT_SESSION_TRACK = 0x00800000;
+        const CLIENT_DEPRECATE_EOF = 0x01000000;
+    }
+}
+
 pub struct ConnectionOptions {
     host: Option<CString>,
     user: CString,
     password: Option<CString>,
     database: Option<CString>,
     port: Option<u16>,
     unix_socket: Option<CString>,
+    client_flags: CapabilityFlags,
 }
 
 impl ConnectionOptions {
@@ -59,13 +90,17 @@ impl ConnectionOptions {
             Some(segment) => Some(CString::new(segment.as_bytes())?),
         };
 
+        // this is not present in the database_url, using a default value
+        let client_flags = CapabilityFlags::CLIENT_FOUND_ROWS;
+
         Ok(ConnectionOptions {
             host: host,
             user: user,
             password: password,
             database: database,
             port: url.port(),
             unix_socket: unix_socket,
+            client_flags: client_flags,
         })
     }
 
@@ -92,6 +127,10 @@ impl ConnectionOptions {
     pub fn unix_socket(&self) -> Option<&CStr> {
         self.unix_socket.as_deref()
     }
+
+    pub fn client_flags(&self) -> CapabilityFlags {
+        self.client_flags
+    }
 }
 
 fn decode_into_cstring(s: &str) -> ConnectionResult<CString> {