feat: make T: /*snip */ impl Component a feature flag

Cargo.toml

@@ -19,14 +19,16 @@ rustdoc-args = ["--cfg", "docsrs"]
 maintenance = { status = "actively-developed" }
 
 [features]
-default = ["std"]
+default = ["std", "blanket-component"]
 std = []
 # Enables derive(Bundle) and derive(Query)
 macros = ["hecs-macros"]
 # Enables the serialize::column module
 column-serialize = ["serde"]
 # Enables the serialize::row module
 row-serialize = ["serde"]
+# enables all T to implement Component
+blanket-component = []
 
 [dependencies]
 hecs-macros = { path = "macros", version = "0.11.1", optional = true }

src/world.rs

@@ -1047,11 +1047,13 @@ impl From<NoSuchEntity> for QueryOneError {
     }
 }
 
-/// Types that can be components, implemented automatically for all `Send + Sync + 'static` types
+/// Types that can be components.
 ///
-/// This is just a convenient shorthand for `Send + Sync + 'static`, and never needs to be
-/// implemented manually.
+/// With the default features enabled, Component is implemented for all `Send + Sync + 'static` types.
+/// Otherwise, users must implement component for each type on their own.
 pub trait Component: Send + Sync + 'static {}
+
+#[cfg(feature = "blanket-component")]
 impl<T: Send + Sync + 'static> Component for T {}
 
 /// Iterator over all of a world's entities