generate docs for feature gated items (#1332)

* generate docs for feature-gated items on crates.io

* add newline in Cargo.toml

* unify newlines

* fix clippy

* introduce macros for features

* commit missing file

* Update subxt/src/lib.rs

* make it compile

subxt/src/macros.rs

@@ -0,0 +1,59 @@
+// Copyright 2019-2023 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+macro_rules! cfg_feature {
+	($feature:literal, $($item:item)*) => {
+		$(
+			#[cfg(feature = $feature)]
+			#[cfg_attr(docsrs, doc(cfg(feature = $feature)))]
+			$item
+		)*
+	}
+}
+
+macro_rules! cfg_substrate_compat {
+	($($item:item)*) => {
+		crate::macros::cfg_feature!("substrate-compat", $($item)*);
+	};
+}
+
+macro_rules! cfg_unstable_light_client {
+	($($item:item)*) => {
+		crate::macros::cfg_feature!("unstable-light-client", $($item)*);
+	};
+}
+
+macro_rules! cfg_jsonrpsee {
+	($($item:item)*) => {
+		crate::macros::cfg_feature!("jsonrpsee", $($item)*);
+	};
+}
+
+#[allow(unused)]
+macro_rules! cfg_jsonrpsee_native {
+	($($item:item)*) => {
+		$(
+			#[cfg(all(feature = "jsonrpsee", feature = "native"))]
+			#[cfg_attr(docsrs, doc(cfg(all(feature = "jsonrpsee", feature = "native"))))]
+			$item
+		)*
+	}
+}
+
+#[allow(unused)]
+macro_rules! cfg_jsonrpsee_web {
+	($($item:item)*) => {
+		$(
+			#[cfg(all(feature = "jsonrpsee", feature = "web"))]
+			#[cfg_attr(docsrs, doc(cfg(all(feature = "jsonrpsee", feature = "web"))))]
+			$item
+		)*
+	}
+}
+
+pub(crate) use {cfg_feature, cfg_jsonrpsee, cfg_substrate_compat, cfg_unstable_light_client};
+
+// Only used by light-client.
+#[allow(unused)]
+pub(crate) use {cfg_jsonrpsee_native, cfg_jsonrpsee_web};