skip COM_STMT_PREPARE in MySQL when statement_cache_capacity=0

rust-toolchain.toml

@@ -1,4 +1,4 @@
 # Note: should NOT increase during a minor/patch release cycle
 [toolchain]
-channel = "1.78"
+channel = "1.88"
 profile = "minimal"

sqlx-mysql/Cargo.toml

@@ -49,6 +49,14 @@ rust_decimal = { workspace = true, optional = true }
 time = { workspace = true, optional = true }
 uuid = { workspace = true, optional = true }
 
+# Vendored patch: client-side parameter interpolation when
+# `statement_cache_capacity == 0`. We use only `mysql_common::Value::as_sql`
+# for canonical MySQL-client quoting/escaping. mysql_common's default
+# features select a flate2 backend (required for it to compile); we unify
+# flate2 to its pure-Rust `rust_backend` here so we don't pull in libz-sys.
+mysql_common = { version = "0.37", default-features = false }
+flate2 = { version = "1", default-features = false, features = ["rust_backend"] }
+
 # Misc
 atoi = "2.0"
 base64 = { version = "0.22.0", default-features = false, features = ["std"] }

sqlx-mysql/src/connection/executor.rs

@@ -118,7 +118,21 @@ impl MySqlConnection {
             let mut columns = Arc::new(Vec::new());
 
             let (mut column_names, format, mut needs_metadata) = if let Some(arguments) = arguments {
-                if persistent && self.inner.cache_statement.is_enabled() {
+                if !self.inner.cache_statement.is_enabled() {
+                    // Vendored patch: when the prepared-statement cache is
+                    // disabled, skip COM_STMT_PREPARE entirely. Interpolate
+                    // bind values into the SQL and send a plain COM_QUERY.
+                    let no_backslash_escape = self.inner.status_flags.contains(
+                        Status::SERVER_STATUS_NO_BACKSLASH_ESCAPES,
+                    );
+                    let interpolated = super::text_query::interpolate(
+                        sql,
+                        &arguments,
+                        no_backslash_escape,
+                    )?;
+                    self.inner.stream.send_packet(Query(&interpolated)).await?;
+                    (Arc::default(), MySqlValueFormat::Text, true)
+                } else if persistent && self.inner.cache_statement.is_enabled() {
                     let (id, metadata) = self
                         .get_or_prepare_statement(sql)
                         .await?;

sqlx-mysql/src/connection/mod.rs

@@ -19,6 +19,7 @@ mod auth;
 mod establish;
 mod executor;
 mod stream;
+mod text_query;
 mod tls;
 
 const MAX_PACKET_SIZE: u32 = 1024;