docs: enhance code documentation

Pull-Request: #5198.

libp2p/src/builder/phase/provider.rs

@@ -1,46 +1,60 @@
 #[allow(unused_imports)]
 use super::*;
-
 use crate::SwarmBuilder;
+use std::marker::PhantomData;
+/// Represents the phase where a provider is not yet specified.
+/// This is a marker type used in the type-state pattern to ensure compile-time checks of the builder's state.
+pub enum NoProviderSpecified {}
+
+// Define enums for each of the possible runtime environments. These are used as markers in the type-state pattern,
+// allowing compile-time checks for the appropriate environment configuration.
+
+#[cfg(all(not(target_arch = "wasm32"), feature = "async-std"))]
+/// Represents the AsyncStd runtime environment.
+pub enum AsyncStd {}
+
+#[cfg(all(not(target_arch = "wasm32"), feature = "tokio"))]
+/// Represents the Tokio runtime environment.
+pub enum Tokio {}
+
+#[cfg(feature = "wasm-bindgen")]
+/// Represents the WasmBindgen environment for WebAssembly.
+pub enum WasmBindgen {}
 
+/// Represents a phase in the SwarmBuilder where a provider has been chosen but not yet specified.
 pub struct ProviderPhase {}
 
 impl SwarmBuilder<NoProviderSpecified, ProviderPhase> {
+    /// Configures the SwarmBuilder to use the AsyncStd runtime.
+    /// This method is only available when compiling for non-Wasm targets with the `async-std` feature enabled.
     #[cfg(all(not(target_arch = "wasm32"), feature = "async-std"))]
     pub fn with_async_std(self) -> SwarmBuilder<AsyncStd, TcpPhase> {
         SwarmBuilder {
             keypair: self.keypair,
-            phantom: std::marker::PhantomData,
+            phantom: PhantomData,
             phase: TcpPhase {},
         }
     }
 
+    /// Configures the SwarmBuilder to use the Tokio runtime.
+    /// This method is only available when compiling for non-Wasm targets with the `tokio` feature enabled
     #[cfg(all(not(target_arch = "wasm32"), feature = "tokio"))]
     pub fn with_tokio(self) -> SwarmBuilder<Tokio, TcpPhase> {
         SwarmBuilder {
             keypair: self.keypair,
-            phantom: std::marker::PhantomData,
+            phantom: PhantomData,
             phase: TcpPhase {},
         }
     }
 
+    /// Configures the SwarmBuilder for WebAssembly using WasmBindgen.
+    /// This method is available when the `wasm-bindgen` feature is enabled.
     #[cfg(feature = "wasm-bindgen")]
     pub fn with_wasm_bindgen(self) -> SwarmBuilder<WasmBindgen, TcpPhase> {
         SwarmBuilder {
             keypair: self.keypair,
-            phantom: std::marker::PhantomData,
+            phantom: PhantomData,
             phase: TcpPhase {},
         }
     }
 }
-
-pub enum NoProviderSpecified {}
-
-#[cfg(all(not(target_arch = "wasm32"), feature = "async-std"))]
-pub enum AsyncStd {}
-
-#[cfg(all(not(target_arch = "wasm32"), feature = "tokio"))]
-pub enum Tokio {}
-
-#[cfg(feature = "wasm-bindgen")]
-pub enum WasmBindgen {}