fix: limit server_fn server macro trybuild tests nightly only

Cargo.lock

@@ -3323,6 +3323,7 @@ dependencies = [
  "reqwest",
  "rkyv",
  "rmp-serde",
+ "rustc_version",
  "rustversion",
  "send_wrapper",
  "serde",

server_fn/Cargo.toml

@@ -16,7 +16,7 @@ server_fn_macro_default = { workspace = true }
 const_format = "0.2.33"
 const-str = "0.6.2"
 xxhash-rust = { version = "0.8.12", features = ["const_xxh64"] }
-rustversion = { workspace = true}
+rustversion = { workspace = true }
 # used across multiple features
 serde = { version = "1.0", features = ["derive"] }
 send_wrapper = { version = "0.6.0", features = ["futures"], optional = true }
@@ -82,6 +82,9 @@ url = "2"
 pin-project-lite = "0.2.15"
 tokio = { version = "1.43.0", features = ["rt"], optional = true }
 
+[build-dependencies]
+rustc_version = "0.4.1"
+
 [dev-dependencies]
 trybuild = { workspace = true }
 
@@ -238,4 +241,7 @@ skip_feature_sets = [
 max_combination_size = 2
 
 [lints.rust]
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(leptos_debuginfo)'] }
+unexpected_cfgs = { level = "warn", check-cfg = [
+  'cfg(leptos_debuginfo)',
+  'cfg(rustc_nightly)',
+] }

server_fn/build.rs

@@ -0,0 +1,8 @@
+use rustc_version::{version_meta, Channel};
+
+fn main() {
+    // Set cfg flags depending on release channel
+    if matches!(version_meta().unwrap().channel, Channel::Nightly) {
+        println!("cargo:rustc-cfg=rustc_nightly");
+    }
+}

server_fn/tests/server_macro.rs

@@ -3,6 +3,7 @@
 // multiple combinations of features are tested. This ensures this file is only
 // run when **only** the browser feature is enabled.
 #![cfg(all(
+    rustc_nightly,
     feature = "browser",
     not(any(
         feature = "postcard",