Allow building payjoin crate with no default features

README.md

@@ -26,6 +26,16 @@
 
 The Payjoin Dev Kit `payjoin` library implements both [BIP 78 Payjoin V1](https://github.com/bitcoin/bips/blob/master/bip-0078.mediawiki) and [BIP 77 Payjoin V2](https://github.com/bitcoin/bips/blob/master/bip-0077.md).
 
+### Feature Flags
+
+The `payjoin` crate supports the following features:
+- `v1`: Enables BIP 78 Payjoin V1 support.
+- `v2`: Enables BIP 77 Payjoin V2 support (enabled by default).
+- `directory`: Enables Payjoin Directory support.
+
+**Note:**
+The crate will now build with no features enabled (e.g., `cargo build --no-default-features`), but in this configuration, no functionality is available. This is intended to support comprehensive CI and linting. To use the library, enable at least one of the features above.
+
 ### `payjoin-cli`
 
 The [`payjoin-cli`](https://github.com/payjoin/rust-payjoin/tree/master/payjoin-cli) crate performs no-frills Payjoin as a reference implementation using Bitcoin Core wallet.

payjoin/Cargo.toml

@@ -16,6 +16,8 @@ exclude = ["tests"]
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [features]
+# The crate will build with no features enabled, but will provide no functionality.
+# Enable at least one of: 'v1', 'v2', or 'directory' to use the library.
 default = ["v2"]
 #[doc = "Core features for payjoin state machines"]
 _core = ["bitcoin/rand-std", "serde_json", "url", "bitcoin_uri", "serde", "bitcoin/serde"]

payjoin/src/lib.rs

@@ -18,7 +18,11 @@
 //! **Use at your own risk. This crate has not yet been reviewed by independent Rust and Bitcoin security professionals.**
 
 #[cfg(not(any(feature = "directory", feature = "v1", feature = "v2")))]
-compile_error!("At least one of the features ['directory', 'v1', 'v2'] must be enabled");
+#[doc(hidden)]
+pub mod no_features_enabled {
+    //! This crate was built with no features enabled. No functionality is available.
+    //! Enable at least one of the features: `directory`, `v1`, or `v2`.
+}
 
 #[cfg(any(feature = "v2", feature = "directory"))]
 pub(crate) mod bech32;