Use a global HashSet for void elements lookup in SSR

packages/sycamore/Cargo.toml

@@ -18,6 +18,7 @@ ahash = "0.7.4"
 html-escape = { version = "0.2.9", optional = true }
 indexmap = { version = "1.7.0", features = ["std"] }
 js-sys = "0.3.55"
+once_cell = { version = "1.8.0", optional = true }
 smallvec = "1.6.1"
 sycamore-macro = { path = "../sycamore-macro", version = "=0.6.0" }
 sycamore-reactive = { path = "../sycamore-reactive", version = "=0.6.0" }
@@ -47,7 +48,7 @@ wasm-bindgen-test = "0.3.28"
 [features]
 default = ["dom"]
 dom = []
-ssr = ["html-escape"]
+ssr = ["html-escape", "once_cell"]
 serde = ["sycamore-reactive/serde"]
 
 [[bench]]

packages/sycamore/src/generic_node/ssr_node.rs

@@ -1,20 +1,26 @@
 //! Rendering backend for Server Side Rendering, aka. SSR.
 
 use std::cell::RefCell;
+use std::collections::HashSet;
 use std::hash::{Hash, Hasher};
 use std::rc::{Rc, Weak};
 
 use ahash::AHashMap;
+use once_cell::sync::Lazy;
 use wasm_bindgen::prelude::*;
 
 use crate::generic_node::{EventHandler, GenericNode};
 use crate::reactive::create_root;
 use crate::template::Template;
 
-static VOID_ELEMENTS: &[&str] = &[
-    "area", "base", "br", "col", "embed", "hr", "img", "input", "link", "meta", "param", "source",
-    "track", "wbr", "command", "keygen", "menuitem",
-];
+static VOID_ELEMENTS: Lazy<HashSet<&'static str>> = Lazy::new(|| {
+    vec![
+        "area", "base", "br", "col", "embed", "hr", "img", "input", "link", "meta", "param",
+        "source", "track", "wbr", "command", "keygen", "menuitem",
+    ]
+    .into_iter()
+    .collect()
+});
 
 /// Inner representation for [`SsrNode`].
 #[derive(Debug, Clone)]
@@ -321,7 +327,7 @@ impl WriteToString for Element {
         }
 
         // Check if self-closing tag (void-element).
-        if self.children.is_empty() && VOID_ELEMENTS.iter().any(|tag| tag == &self.name) {
+        if self.children.is_empty() && VOID_ELEMENTS.contains(self.name.as_str()) {
             s.push_str("/>");
         } else {
             s.push('>');