Fix contractenvmetav0 not being emitted (again)

macros/src/derive_fn.rs

@@ -174,13 +174,6 @@ pub fn derive_fn(
         pub mod #hidden_mod_ident {
             use super::*;
 
-            /// Exposing the env meta XDR ensures that the link section in the
-            /// SDK is included in the build for this contract function. See
-            /// [soroban_sdk::__env_meta_xdr] for more details.
-            pub fn env_meta_xdr() -> &'static[u8] {
-                soroban_sdk::__env_meta_xdr()
-            }
-
             #[deprecated(note = #deprecated_note)]
             #export_name
             pub fn invoke_raw(env: soroban_sdk::Env, #(#wrap_args),*) -> soroban_sdk::RawVal {

sdk/src/lib.rs

@@ -8,17 +8,29 @@ fn handle_panic(_: &core::panic::PanicInfo) -> ! {
     core::arch::wasm32::unreachable()
 }
 
-/// Env meta XDR returns the env meta XDR that describes the environment this
-/// SDK is built with. This link section exists inside an exported function
-/// which is imported by each contract function to ensure that the link section
-/// is referenced by every object file that gets built, to ensure the link
-/// section isn't only referenced in an object file that gets discarded.
+/// __link_sections returns and does nothing, but it contains link sections that
+/// should be ensured end up in the final build of any contract using the SDK.
+///
+/// In Rust's build system sections only get included into the final build if
+/// the object file containing those sections are processed by the linker, but
+/// as an optimization step if no code is called in an object file it is
+/// discarded.  This has the unfortunate effect of causing anything else in
+/// those object files, such as link sections, to be discarded. Placing anything
+/// that must be included in the build inside an exported function ensures the
+/// object files won't be discarded. wasm-bindgen does a similar thing to this,
+/// and so this seems to be a reasonably accepted way to work around this
+/// limitation in the build system.
+///
+/// This has an unfortunate side-effect that all contracts will have a function
+/// in the resulting WASM named `_`, however this function won't be rendered in
+/// the contract specification. The overhead of this is very minimal on file
+/// size.
+///
 /// See https://github.com/stellar/rs-soroban-sdk/issues/383 for more details.
-#[doc(hidden)]
-pub fn __env_meta_xdr() -> &'static [u8] {
+#[export_name = "_"]
+fn __link_sections() {
     #[cfg_attr(target_family = "wasm", link_section = "contractenvmetav0")]
     static __ENV_META_XDR: [u8; env::meta::XDR.len()] = env::meta::XDR;
-    &__ENV_META_XDR
 }
 
 pub use soroban_sdk_macros::{contractimpl, contracttype, ContractType};