Error on enums with explicit discriminant values in SpacetimeType

SpacetimeDB's SATS encoding assigns variant tags by declaration
order, ignoring Rust discriminant values. An enum like:

    #[derive(SpacetimeType)]
    enum Foo { A = 5, B = 10 }

would silently encode A as tag 0 and B as tag 1, which is
confusing and error-prone. Emit a compile error instead.

Also removes explicit discriminant values from two internal
enums (UnsubscribeFlags, IndexType) that already matched the
default tag order.

Author: clockwork-labs-bot

crates/bindings-macro/src/sats.rs

@@ -64,6 +64,12 @@ pub(crate) fn sats_type_from_derive(
         }
         syn::Data::Enum(enu) => {
             let variants = enu.variants.iter().map(|var| {
+                if let Some((eq, _)) = &var.discriminant {
+                    return Err(syn::Error::new(
+                        eq.span(),
+                        "explicit discriminant values are not supported by SpacetimeDB",
+                    ));
+                }
                 let (member, ty) = variant_data(var)?.unzip();
                 Ok(SatsVariant {
                     ident: &var.ident,

crates/client-api-messages/src/websocket/v2.rs

@@ -87,9 +87,9 @@ pub struct Unsubscribe {
 #[sats(crate = spacetimedb_lib)]
 pub enum UnsubscribeFlags {
     #[default]
-    Default = 0,
+    Default,
     // If set, the server will send the full set of rows to be removed from the client cache.
-    SendDroppedRows = 1,
+    SendDroppedRows,
 }
 
 /// Sent by the client to perform a query at a single point in time.

crates/lib/src/db/raw_def/v8.rs

@@ -83,9 +83,9 @@ impl RawSequenceDefV8 {
 #[sats(crate = crate)]
 pub enum IndexType {
     /// A BTree index.
-    BTree = 0,
+    BTree,
     /// A Hash index.
-    Hash = 1,
+    Hash,
 }
 
 impl From<IndexType> for u8 {