[eframe] Make persistence, http and time optional features

Saves on compile times.

egui_web/src/backend.rs

@@ -1,7 +1,6 @@
 use crate::*;
 
 pub use egui::{pos2, Color32};
-use http::WebHttp;
 
 // ----------------------------------------------------------------------------
 
@@ -144,7 +143,8 @@ pub struct AppRunner {
     pub(crate) needs_repaint: std::sync::Arc<NeedRepaint>,
     storage: LocalStorage,
     last_save_time: f64,
-    http: Arc<WebHttp>,
+    #[cfg(feature = "http")]
+    http: Arc<http::WebHttp>,
 }
 
 impl AppRunner {
@@ -160,7 +160,8 @@ impl AppRunner {
             needs_repaint: Default::default(),
             storage,
             last_save_time: now_sec(),
-            http: Arc::new(WebHttp {}),
+            #[cfg(feature = "http")]
+            http: Arc::new(http::WebHttp {}),
         })
     }
 
@@ -210,6 +211,7 @@ impl AppRunner {
                 native_pixels_per_point: Some(native_pixels_per_point()),
             },
             tex_allocator: Some(&mut self.web_backend.painter),
+            #[cfg(feature = "http")]
             http: self.http.clone(),
             output: &mut app_output,
             repaint_signal: self.needs_repaint.clone(),

egui_web/src/lib.rs

@@ -9,6 +9,7 @@
 #![warn(clippy::all, rust_2018_idioms)]
 
 pub mod backend;
+#[cfg(feature = "http")]
 pub mod http;
 pub mod webgl;
 
@@ -154,6 +155,7 @@ pub fn local_storage_remove(key: &str) {
     local_storage().map(|storage| storage.remove_item(key));
 }
 
+#[cfg(feature = "persistence")]
 pub fn load_memory(ctx: &egui::Context) {
     if let Some(memory_string) = local_storage_get("egui_memory_json") {
         match serde_json::from_str(&memory_string) {
@@ -167,6 +169,10 @@ pub fn load_memory(ctx: &egui::Context) {
     }
 }
 
+#[cfg(not(feature = "persistence"))]
+pub fn load_memory(_: &egui::Context) {}
+
+#[cfg(feature = "persistence")]
 pub fn save_memory(ctx: &egui::Context) {
     match serde_json::to_string(&*ctx.memory()) {
         Ok(json) => {
@@ -178,6 +184,9 @@ pub fn save_memory(ctx: &egui::Context) {
     }
 }
 
+#[cfg(not(feature = "persistence"))]
+pub fn save_memory(_: &egui::Context) {}
+
 #[derive(Default)]
 pub struct LocalStorage {}