From 47148f20334ec4641ef36bee6f69e89afdf66b58 Mon Sep 17 00:00:00 2001
From: Greg Johnston <greg.johnston@gmail.com>
Date: Mon, 17 Jul 2023 12:20:33 -0400
Subject: [PATCH] perf: exclude hydration code in CSR mode (#1372)

---
 leptos/Cargo.toml           |  4 ++--
 leptos_dom/Cargo.toml       |  4 +++-
 leptos_dom/src/hydration.rs | 35 ++++++++++++++++++++---------------
 leptos_dom/src/lib.rs       |  7 +++++++
 4 files changed, 32 insertions(+), 18 deletions(-)

diff --git a/leptos/Cargo.toml b/leptos/Cargo.toml
index e2e324cea..79e63daab 100644
--- a/leptos/Cargo.toml
+++ b/leptos/Cargo.toml
@@ -28,13 +28,13 @@ leptos = { path = "." }
 default = ["serde"]
 template_macro = ["leptos_dom/web", "web-sys", "wasm-bindgen"]
 csr = [
-  "leptos_dom/web",
+  "leptos_dom/csr",
   "leptos_macro/csr",
   "leptos_reactive/csr",
   "leptos_server/csr",
 ]
 hydrate = [
-  "leptos_dom/web",
+  "leptos_dom/hydrate",
   "leptos_macro/hydrate",
   "leptos_reactive/hydrate",
   "leptos_server/hydrate",
diff --git a/leptos_dom/Cargo.toml b/leptos_dom/Cargo.toml
index 5ce9401c3..af8f0786a 100644
--- a/leptos_dom/Cargo.toml
+++ b/leptos_dom/Cargo.toml
@@ -164,7 +164,9 @@ features = [
 
 [features]
 default = []
-web = ["leptos_reactive/csr"]
+web = []
+csr = ["leptos_reactive/csr", "web"]
+hydrate = ["leptos_reactive/hydrate", "web"]
 ssr = ["leptos_reactive/ssr"]
 nightly = ["leptos_reactive/nightly"]
 nonce = ["dep:base64", "dep:getrandom", "dep:rand"]
diff --git a/leptos_dom/src/hydration.rs b/leptos_dom/src/hydration.rs
index ad8965efc..7a89001a1 100644
--- a/leptos_dom/src/hydration.rs
+++ b/leptos_dom/src/hydration.rs
@@ -1,17 +1,16 @@
-use cfg_if::cfg_if;
 use std::{cell::RefCell, fmt::Display};
 
-cfg_if! {
-  if #[cfg(all(target_arch = "wasm32", feature = "web"))] {
+#[cfg(all(target_arch = "wasm32", feature = "hydrate"))]
+mod hydration {
     use once_cell::unsync::Lazy as LazyCell;
-    use std::collections::HashMap;
+    use std::{cell::RefCell, collections::HashMap};
     use wasm_bindgen::JsCast;
 
     // We can tell if we start in hydration mode by checking to see if the
     // id "_0-1" is present in the DOM. If it is, we know we are hydrating from
     // the server, if not, we are starting off in CSR
     thread_local! {
-      static HYDRATION_COMMENTS: LazyCell<HashMap<String, web_sys::Comment>> = LazyCell::new(|| {
+      pub static HYDRATION_COMMENTS: LazyCell<HashMap<String, web_sys::Comment>> = LazyCell::new(|| {
         let document = crate::document();
         let body = document.body().unwrap();
         let walker = document
@@ -31,7 +30,7 @@ cfg_if! {
       });
 
       #[cfg(debug_assertions)]
-      pub(crate) static VIEW_MARKERS: LazyCell<HashMap<String, web_sys::Comment>> = LazyCell::new(|| {
+      pub static VIEW_MARKERS: LazyCell<HashMap<String, web_sys::Comment>> = LazyCell::new(|| {
         let document = crate::document();
         let body = document.body().unwrap();
         let walker = document
@@ -48,7 +47,7 @@ cfg_if! {
         map
       });
 
-      static IS_HYDRATING: RefCell<LazyCell<bool>> = RefCell::new(LazyCell::new(|| {
+      pub static IS_HYDRATING: RefCell<LazyCell<bool>> = RefCell::new(LazyCell::new(|| {
         #[cfg(debug_assertions)]
         return crate::document().get_element_by_id("_0-1").is_some()
           || crate::document().get_element_by_id("_0-1o").is_some()
@@ -60,12 +59,14 @@ cfg_if! {
       }));
     }
 
-    pub(crate) fn get_marker(id: &str) -> Option<web_sys::Comment> {
-      HYDRATION_COMMENTS.with(|comments| comments.get(id).cloned())
+    pub fn get_marker(id: &str) -> Option<web_sys::Comment> {
+        HYDRATION_COMMENTS.with(|comments| comments.get(id).cloned())
     }
-  }
 }
 
+#[cfg(all(target_arch = "wasm32", feature = "hydrate"))]
+pub(crate) use hydration::*;
+
 /// A stable identifier within the server-rendering or hydration process.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Default)]
 pub struct HydrationKey {
@@ -125,23 +126,27 @@ impl HydrationCtx {
 
     #[cfg(all(target_arch = "wasm32", feature = "web"))]
     pub(crate) fn stop_hydrating() {
-        IS_HYDRATING.with(|is_hydrating| {
-            std::mem::take(&mut *is_hydrating.borrow_mut());
-        })
+        #[cfg(feature = "hydrate")]
+        {
+            IS_HYDRATING.with(|is_hydrating| {
+                std::mem::take(&mut *is_hydrating.borrow_mut());
+            })
+        }
     }
 
     /// Whether the UI is currently in the process of hydrating from the server-sent HTML.
     pub fn is_hydrating() -> bool {
-        #[cfg(all(target_arch = "wasm32", feature = "web"))]
+        #[cfg(all(target_arch = "wasm32", feature = "hydrate"))]
         {
             IS_HYDRATING.with(|is_hydrating| **is_hydrating.borrow())
         }
-        #[cfg(not(all(target_arch = "wasm32", feature = "web")))]
+        #[cfg(not(all(target_arch = "wasm32", feature = "hydrate")))]
         {
             false
         }
     }
 
+    #[allow(dead_code)] // not used in CSR
     pub(crate) fn to_string(id: &HydrationKey, closing: bool) -> String {
         #[cfg(debug_assertions)]
         return format!("_{id}{}", if closing { 'c' } else { 'o' });
diff --git a/leptos_dom/src/lib.rs b/leptos_dom/src/lib.rs
index 0721f292a..399db5800 100644
--- a/leptos_dom/src/lib.rs
+++ b/leptos_dom/src/lib.rs
@@ -416,11 +416,18 @@ impl Comment {
 
                 Self { content }
             } else {
+                #[cfg(not(feature = "hydrate"))]
+                {
+                    _ = id;
+                    _ = closing;
+                }
+
                 let node = COMMENT.with(|comment| comment.clone_node().unwrap());
 
                 #[cfg(debug_assertions)]
                 node.set_text_content(Some(&format!(" {content} ")));
 
+                #[cfg(feature = "hydrate")]
                 if HydrationCtx::is_hydrating() {
                     let id = HydrationCtx::to_string(id, closing);