Dont generate connection_ids in the rust client. (#3004)

# Description of Changes

This changes the behavior on the rust client, so that we let the server
generate the connection id if the client hasn't called the unstable
method to set a connection id.

This is awkward for the `connection_id` function, since it now panics if
the connection id hasn't been received from the server. We should
deprecate this function in favor of a `try` version.

This also changes the behavior of reusing the connection id if a client
reconnects.

The corresponding private PR is
clockworklabs/SpacetimeDBPrivate#1921.

# API and ABI breaking changes

Technically not changing any API signatures, but this is
behavior-changing, since the `connection_id` function can now panic.

# Expected complexity level and risk

2. The risk here is people relying on that behavior.

# Testing

I think some tests need to be updated.

Author: jsdt

crates/codegen/src/rust.rs

@@ -1272,6 +1272,9 @@ impl __sdk::DbContext for DbConnection {{
     fn connection_id(&self) -> __sdk::ConnectionId {{
         self.imp.connection_id()
     }}
+    fn try_connection_id(&self) -> Option<__sdk::ConnectionId> {{
+        self.imp.try_connection_id()
+    }}
 }}
 
 impl DbConnection {{
@@ -1588,6 +1591,9 @@ impl __sdk::DbContext for {struct_and_trait_name} {{
     fn connection_id(&self) -> __sdk::ConnectionId {{
         self.imp.connection_id()
     }}
+    fn try_connection_id(&self) -> Option<__sdk::ConnectionId> {{
+        self.imp.try_connection_id()
+    }}
 }}
 
 impl __sdk::{struct_and_trait_name} for {struct_and_trait_name} {{}}

crates/codegen/tests/snapshots/codegen__codegen_rust.snap

@@ -1814,6 +1814,9 @@ impl __sdk::DbContext for DbConnection {
     fn connection_id(&self) -> __sdk::ConnectionId {
         self.imp.connection_id()
     }
+    fn try_connection_id(&self) -> Option<__sdk::ConnectionId> {
+        self.imp.try_connection_id()
+    }
 }
 
 impl DbConnection {
@@ -2027,6 +2030,9 @@ impl __sdk::DbContext for EventContext {
     fn connection_id(&self) -> __sdk::ConnectionId {
         self.imp.connection_id()
     }
+    fn try_connection_id(&self) -> Option<__sdk::ConnectionId> {
+        self.imp.try_connection_id()
+    }
 }
 
 impl __sdk::EventContext for EventContext {}
@@ -2103,6 +2109,9 @@ impl __sdk::DbContext for ReducerEventContext {
     fn connection_id(&self) -> __sdk::ConnectionId {
         self.imp.connection_id()
     }
+    fn try_connection_id(&self) -> Option<__sdk::ConnectionId> {
+        self.imp.try_connection_id()
+    }
 }
 
 impl __sdk::ReducerEventContext for ReducerEventContext {}
@@ -2175,6 +2184,9 @@ impl __sdk::DbContext for SubscriptionEventContext {
     fn connection_id(&self) -> __sdk::ConnectionId {
         self.imp.connection_id()
     }
+    fn try_connection_id(&self) -> Option<__sdk::ConnectionId> {
+        self.imp.try_connection_id()
+    }
 }
 
 impl __sdk::SubscriptionEventContext for SubscriptionEventContext {}
@@ -2251,6 +2263,9 @@ impl __sdk::DbContext for ErrorContext {
     fn connection_id(&self) -> __sdk::ConnectionId {
         self.imp.connection_id()
     }
+    fn try_connection_id(&self) -> Option<__sdk::ConnectionId> {
+        self.imp.try_connection_id()
+    }
 }
 
 impl __sdk::ErrorContext for ErrorContext {}

crates/sdk/examples/quickstart-chat/main.rs

@@ -63,22 +63,22 @@ fn creds_store() -> credentials::File {
 /// Our `on_connect` callback: save our credentials to a file.
 fn on_connected(_ctx: &DbConnection, _identity: Identity, token: &str) {
     if let Err(e) = creds_store().save(token) {
-        eprintln!("Failed to save credentials: {:?}", e);
+        eprintln!("Failed to save credentials: {e:?}");
     }
 }
 
 // ### Handle errors and disconnections
 
 /// Our `on_connect_error` callback: print the error, then exit the process.
 fn on_connect_error(_ctx: &ErrorContext, err: Error) {
-    eprintln!("Connection error: {}", err);
+    eprintln!("Connection error: {err}");
     std::process::exit(1);
 }
 
 /// Our `on_disconnect` callback: print a note, then exit the process.
 fn on_disconnected(_ctx: &ErrorContext, err: Option<Error>) {
     if let Some(err) = err {
-        eprintln!("Disconnected: {}", err);
+        eprintln!("Disconnected: {err}");
         std::process::exit(1);
     } else {
         println!("Disconnected.");
@@ -166,14 +166,14 @@ fn print_message(ctx: &impl RemoteDbContext, message: &Message) {
 /// Our `on_set_name` callback: print a warning if the reducer failed.
 fn on_name_set(ctx: &ReducerEventContext, name: &String) {
     if let Status::Failed(err) = &ctx.event.status {
-        eprintln!("Failed to change name to {:?}: {}", name, err);
+        eprintln!("Failed to change name to {name:?}: {err}");
     }
 }
 
 /// Our `on_send_message` callback: print a warning if the reducer failed.
 fn on_message_sent(ctx: &ReducerEventContext, text: &String) {
     if let Status::Failed(err) = &ctx.event.status {
-        eprintln!("Failed to send message {:?}: {}", text, err);
+        eprintln!("Failed to send message {text:?}: {err}");
     }
 }
 
@@ -206,7 +206,7 @@ fn on_sub_applied(ctx: &SubscriptionEventContext) {
 /// Or `on_error` callback:
 /// print the error, then exit the process.
 fn on_sub_error(_ctx: &ErrorContext, err: Error) {
-    eprintln!("Subscription failed: {}", err);
+    eprintln!("Subscription failed: {err}");
     std::process::exit(1);
 }