From f3de12bc5e03c58a9b863943b8db84a321422bec Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Fri, 21 Jan 2022 00:29:29 +0000
Subject: [PATCH] Add a warning when `watch_for_changes` has no effect (#3684)

# Objective

- Users can get confused when they ask for watching to be unsupported, then find it isn't supported
- Fixes https://github.com/bevyengine/bevy/issues/3683

## Solution

- Add a warning if the `watch_for_changes` call would do nothing
---
 crates/bevy_asset/src/io/android_asset_io.rs | 1 +
 crates/bevy_asset/src/io/file_asset_io.rs    | 2 ++
 crates/bevy_asset/src/io/wasm_asset_io.rs    | 1 +
 3 files changed, 4 insertions(+)

diff --git a/crates/bevy_asset/src/io/android_asset_io.rs b/crates/bevy_asset/src/io/android_asset_io.rs
index 91aa3770e1..4397dcae63 100644
--- a/crates/bevy_asset/src/io/android_asset_io.rs
+++ b/crates/bevy_asset/src/io/android_asset_io.rs
@@ -42,6 +42,7 @@ impl AssetIo for AndroidAssetIo {
     }
 
     fn watch_for_changes(&self) -> Result<(), AssetIoError> {
+        bevy_log::warn!("Watching for changes is not supported on Android");
         Ok(())
     }
 
diff --git a/crates/bevy_asset/src/io/file_asset_io.rs b/crates/bevy_asset/src/io/file_asset_io.rs
index a7124c5982..1bd7f1515c 100644
--- a/crates/bevy_asset/src/io/file_asset_io.rs
+++ b/crates/bevy_asset/src/io/file_asset_io.rs
@@ -104,6 +104,8 @@ impl AssetIo for FileAssetIo {
         {
             *self.filesystem_watcher.write() = Some(FilesystemWatcher::default());
         }
+        #[cfg(not(feature = "filesystem_watcher"))]
+        bevy_log::warn!("Watching for changes is not supported when the `filesystem_watcher` feature is disabled");
 
         Ok(())
     }
diff --git a/crates/bevy_asset/src/io/wasm_asset_io.rs b/crates/bevy_asset/src/io/wasm_asset_io.rs
index 3e66981edc..a4e260d6fe 100644
--- a/crates/bevy_asset/src/io/wasm_asset_io.rs
+++ b/crates/bevy_asset/src/io/wasm_asset_io.rs
@@ -46,6 +46,7 @@ impl AssetIo for WasmAssetIo {
     }
 
     fn watch_for_changes(&self) -> Result<(), AssetIoError> {
+        bevy_log::warn!("Watching for changes is not supported in WASM");
         Ok(())
     }