Drop no-std feature

We drop the `lightning/no-std` feature and just take
`hashbrown`,`possiblyrandom` and `libm` as required dependencies.

.github/workflows/build.yml

@@ -149,16 +149,11 @@ jobs:
         run: |
           cd lightning
           RUSTFLAGS="--cfg=require_route_graph_test" cargo test
-          RUSTFLAGS="--cfg=require_route_graph_test" cargo test --features hashbrown
           cd ..
       - name: Run benchmarks on Rust ${{ matrix.toolchain }}
         run: |
           cd bench
           RUSTFLAGS="--cfg=ldk_bench --cfg=require_route_graph_test" cargo bench
-      - name: Run benchmarks with hashbrown on Rust ${{ matrix.toolchain }}
-        run: |
-          cd bench
-          RUSTFLAGS="--cfg=ldk_bench --cfg=require_route_graph_test" cargo bench --features hashbrown
 
   check_commits:
     runs-on: ubuntu-latest
@@ -199,15 +194,15 @@ jobs:
       - name: Run cargo check for release build.
         run: |
           cargo check --release
-          cargo check --no-default-features --features=no-std --release
           cargo check --no-default-features --features=futures,std --release
           cargo doc --release
       - name: Run cargo check for Taproot build.
         run: |
           cargo check --release
-          cargo check --no-default-features --features=no-std --release
+          cargo check --no-default-features --release
           cargo check --no-default-features --features=futures,std --release
           cargo doc --release
+          cargo doc --no-default-features --release
         env:
           RUSTFLAGS: '--cfg=taproot'
           RUSTDOCFLAGS: '--cfg=taproot'

Cargo.toml

@@ -1,6 +1,8 @@
 [workspace]
 resolver = "2"
 
+# When the workspace members change, make sure to update the list here as well
+# as in `ci/ci-tests.sh`.
 members = [
     "lightning",
     "lightning-types",

README.md

@@ -27,7 +27,7 @@ Crates
 -----------
 1. [lightning](./lightning)
   The core of the LDK library, implements the Lightning protocol, channel state machine,
-  and on-chain logic. Supports `no-std` and exposes only relatively low-level interfaces.
+  and on-chain logic. Supports `no_std` and exposes only relatively low-level interfaces.
 2. [lightning-background-processor](./lightning-background-processor)
   Utilities to perform required background tasks for Rust Lightning.
 3. [lightning-block-sync](./lightning-block-sync)

bench/Cargo.toml

@@ -8,9 +8,6 @@ edition = "2021"
 name = "bench"
 harness = false
 
-[features]
-hashbrown = ["lightning/hashbrown"]
-
 [dependencies]
 lightning = { path = "../lightning", features = ["_test_utils", "criterion"] }
 lightning-persister = { path = "../lightning-persister", features = ["criterion"] }

bench/README.md

@@ -1,6 +1,3 @@
 This crate uses criterion to benchmark various LDK functions.
 
 It can be run as `RUSTFLAGS=--cfg=ldk_bench cargo bench`.
-
-For routing or other HashMap-bottlenecked functions, the `hashbrown` feature
-should also be benchmarked.

ci/check-compiles.sh

@@ -6,5 +6,5 @@ cargo check
 cargo doc
 cargo doc --document-private-items
 cd fuzz && RUSTFLAGS="--cfg=fuzzing --cfg=secp256k1_fuzz --cfg=hashes_fuzz" cargo check --features=stdin_fuzz
-cd ../lightning && cargo check --no-default-features --features=no-std
+cd ../lightning && cargo check --no-default-features
 cd .. && RUSTC_BOOTSTRAP=1 RUSTFLAGS="--cfg=c_bindings" cargo check -Z avoid-dev-deps

ci/ci-tests.sh

@@ -33,6 +33,8 @@ export RUST_BACKTRACE=1
 echo -e "\n\nChecking the full workspace."
 cargo check --verbose --color always
 
+# When the workspace members change, make sure to update the list here as well
+# as in `Cargo.toml`.
 WORKSPACE_MEMBERS=(
 	lightning
 	lightning-types
@@ -100,38 +102,36 @@ grep '^max_level_' lightning/Cargo.toml | awk '{ print $1 }'| while read -r FEAT
 	RUSTFLAGS="$RUSTFLAGS -A unused_variables -A unused_macros -A unused_imports -A dead_code" cargo check -p lightning --verbose --color always --features "$FEATURE"
 done
 
-echo -e "\n\nTesting no-std builds"
+echo -e "\n\nTesting no_std builds"
 for DIR in lightning-invoice lightning-rapid-gossip-sync; do
 	cargo test -p $DIR --verbose --color always --no-default-features
 done
 
-cargo test -p lightning --verbose --color always --no-default-features --features no-std
-# check if there is a conflict between no-std and the default std feature
-cargo test -p lightning --verbose --color always --features no-std
+cargo test -p lightning --verbose --color always --no-default-features
 
 echo -e "\n\nTesting c_bindings builds"
 # Note that because `$RUSTFLAGS` is not passed through to doctest builds we cannot selectively
 # disable doctests in `c_bindings` so we skip doctests entirely here.
 RUSTFLAGS="$RUSTFLAGS --cfg=c_bindings" cargo test --verbose --color always --lib --bins --tests
 
 for DIR in lightning-invoice lightning-rapid-gossip-sync; do
-	# check if there is a conflict between no-std and the c_bindings cfg
+	# check if there is a conflict between no_std and the c_bindings cfg
 	RUSTFLAGS="$RUSTFLAGS --cfg=c_bindings" cargo test -p $DIR --verbose --color always --no-default-features
 done
 
 # Note that because `$RUSTFLAGS` is not passed through to doctest builds we cannot selectively
 # disable doctests in `c_bindings` so we skip doctests entirely here.
 RUSTFLAGS="$RUSTFLAGS --cfg=c_bindings" cargo test -p lightning-background-processor --verbose --color always --features futures --no-default-features --lib --bins --tests
-RUSTFLAGS="$RUSTFLAGS --cfg=c_bindings" cargo test -p lightning --verbose --color always --no-default-features --features=no-std --lib --bins --tests
+RUSTFLAGS="$RUSTFLAGS --cfg=c_bindings" cargo test -p lightning --verbose --color always --no-default-features --lib --bins --tests
 
 echo -e "\n\nTesting other crate-specific builds"
 # Note that outbound_commitment_test only runs in this mode because of hardcoded signature values
 RUSTFLAGS="$RUSTFLAGS --cfg=ldk_test_vectors" cargo test -p lightning --verbose --color always --no-default-features --features=std
 # This one only works for lightning-invoice
-# check that compile with no-std and serde works in lightning-invoice
+# check that compile with no_std and serde works in lightning-invoice
 cargo test -p lightning-invoice --verbose --color always --no-default-features --features serde
 
-echo -e "\n\nTesting no-std build on a downstream no-std crate"
+echo -e "\n\nTesting no_std build on a downstream no-std crate"
 # check no-std compatibility across dependencies
 pushd no-std-check
 cargo check --verbose --color always --features lightning-transaction-sync

fuzz/Cargo.toml

@@ -18,7 +18,7 @@ libfuzzer_fuzz = ["libfuzzer-sys"]
 stdin_fuzz = []
 
 [dependencies]
-lightning = { path = "../lightning", features = ["regex", "hashbrown", "_test_utils"] }
+lightning = { path = "../lightning", features = ["regex", "_test_utils"] }
 lightning-invoice = { path = "../lightning-invoice" }
 lightning-rapid-gossip-sync = { path = "../lightning-rapid-gossip-sync" }
 bech32 = "0.9.1"

lightning-background-processor/src/lib.rs

@@ -1,7 +1,6 @@
 //! Utilities that take care of tasks that (1) need to happen periodically to keep Rust-Lightning
-//! running properly, and (2) either can or should be run in the background. See docs for
-//! [`BackgroundProcessor`] for more details on the nitty-gritty.
-
+//! running properly, and (2) either can or should be run in the background.
+#![cfg_attr(feature = "std", doc = "See docs for [`BackgroundProcessor`] for more details.")]
 #![deny(rustdoc::broken_intra_doc_links)]
 #![deny(rustdoc::private_intra_doc_links)]
 #![deny(missing_docs)]

lightning-rapid-gossip-sync/src/lib.rs

@@ -35,8 +35,15 @@
 //! Note that the first ever rapid sync should use `0` for `last_sync_timestamp`.
 //!
 //! After the gossip data snapshot has been downloaded, one of the client's graph processing
-//! functions needs to be called. In this example, we process the update by reading its contents
-//! from disk, which we do by calling [`RapidGossipSync::update_network_graph`]:
+//! functions needs to be called.
+#![cfg_attr(
+	feature = "std",
+	doc = "In this example, we process the update by reading its contents from disk, which we do by calling [`RapidGossipSync::update_network_graph`]:"
+)]
+#![cfg_attr(
+	not(feature = "std"),
+	doc = "In this example, we process the update by reading its contents from disk, which we do by calling [`RapidGossipSync::update_network_graph_no_std`]:"
+)]
 //!
 //! ```
 //! use bitcoin::constants::genesis_block;
@@ -54,10 +61,17 @@
 //! let network_graph = NetworkGraph::new(Network::Bitcoin, &logger);
 //! let rapid_sync = RapidGossipSync::new(&network_graph, &logger);
 //! let snapshot_contents: &[u8] = &[0; 0];
-//! // In no-std you need to provide the current time in unix epoch seconds
-//! // otherwise you can use update_network_graph
-//! let current_time_unix = 0;
-//! let new_last_sync_timestamp_result = rapid_sync.update_network_graph_no_std(snapshot_contents, Some(current_time_unix));
+//! // In non-`std` environments you need to provide the current time in unix epoch seconds
+//! // otherwise you can use `update_network_graph`:
+#![cfg_attr(
+	feature = "std",
+	doc = "let new_last_sync_timestamp_result = rapid_sync.update_network_graph(snapshot_contents);"
+)]
+#![cfg_attr(not(feature = "std"), doc = "let current_time_unix = 0;")]
+#![cfg_attr(
+	not(feature = "std"),
+	doc = "let new_last_sync_timestamp_result = rapid_sync.update_network_graph_no_std(snapshot_contents, Some(current_time_unix));"
+)]
 //! ```
 
 #![cfg_attr(all(not(feature = "std"), not(test)), no_std)]

lightning/Cargo.toml

@@ -29,7 +29,6 @@ max_level_trace = []
 # This is unsafe to use in production because it may result in the counterparty publishing taking our funds.
 unsafe_revoked_tx_signing = []
 
-no-std = ["hashbrown", "possiblyrandom", "libm"]
 std = []
 
 # Generates low-r bitcoin signatures, which saves 1 byte in 50% of the cases
@@ -44,12 +43,12 @@ lightning-invoice = { version = "0.32.0", path = "../lightning-invoice", default
 bech32 = { version = "0.9.1", default-features = false }
 bitcoin = { version = "0.32.2", default-features = false, features = ["secp-recovery"] }
 
-hashbrown = { version = "0.13", optional = true, default-features = false }
-possiblyrandom = { version = "0.2", path = "../possiblyrandom", optional = true, default-features = false }
+hashbrown = { version = "0.13", default-features = false }
+possiblyrandom = { version = "0.2", path = "../possiblyrandom", default-features = false }
 regex = { version = "1.5.6", optional = true }
 backtrace = { version = "0.3", optional = true }
 
-libm = { version = "0.2", optional = true, default-features = false }
+libm = { version = "0.2", default-features = false }
 
 [dev-dependencies]
 regex = "1.5.6"

lightning/src/events/mod.rs

@@ -543,12 +543,13 @@ pub enum PaymentFailureReason {
 	///
 	/// [`ChannelManager::abandon_payment`]: crate::ln::channelmanager::ChannelManager::abandon_payment
 	UserAbandoned,
-	/// We exhausted all of our retry attempts while trying to send the payment, or we
-	/// exhausted the [`Retry::Timeout`] if the user set one. If at any point a retry
-	/// attempt failed while being forwarded along the path, an [`Event::PaymentPathFailed`] will
+	#[cfg_attr(feature = "std", doc = "We exhausted all of our retry attempts while trying to send the payment, or we")]
+	#[cfg_attr(feature = "std", doc = "exhausted the [`Retry::Timeout`] if the user set one.")]
+	#[cfg_attr(not(feature = "std"), doc = "We exhausted all of our retry attempts while trying to send the payment.")]
+	/// If at any point a retry attempt failed while being forwarded along the path, an [`Event::PaymentPathFailed`] will
 	/// have come before this.
-	///
-	/// [`Retry::Timeout`]: crate::ln::channelmanager::Retry::Timeout
+	#[cfg_attr(feature = "std", doc = "")]
+	#[cfg_attr(feature = "std", doc = "[`Retry::Timeout`]: crate::ln::channelmanager::Retry::Timeout")]
 	RetriesExhausted,
 	/// The payment expired while retrying, based on the provided
 	/// [`PaymentParameters::expiry_time`].

lightning/src/lib.rs

@@ -28,7 +28,6 @@
 //!
 //! * `std`
 //! * `grind_signatures`
-//! * `no-std ` - exposes write trait implementations from the `core2` crate (at least one of `no-std` or `std` are required)
 //! * Skip logging of messages at levels below the given log level:
 //!     * `max_level_off`
 //!     * `max_level_error`
@@ -53,9 +52,6 @@
 
 #![cfg_attr(all(not(feature = "std"), not(test)), no_std)]
 
-#[cfg(not(any(feature = "std", feature = "no-std")))]
-compile_error!("at least one of the `std` or `no-std` features must be enabled");
-
 #[cfg(all(fuzzing, test))]
 compile_error!("Tests will always fail with cfg=fuzzing");
 

lightning/src/ln/channelmanager.rs

@@ -6042,7 +6042,7 @@ where
 	///  * Forgetting about stale outbound payments, either those that have already been fulfilled
 	///    or those awaiting an invoice that hasn't been delivered in the necessary amount of time.
 	///    The latter is determined using the system clock in `std` and the highest seen block time
-	///    minus two hours in `no-std`.
+	///    minus two hours in non-`std`.
 	///
 	/// Note that this may cause reentrancy through [`chain::Watch::update_channel`] calls or feerate
 	/// estimate fetches.
@@ -9064,7 +9064,7 @@ macro_rules! create_refund_builder { ($self: ident, $builder: ty) => {
 	/// See [Avoiding Duplicate Payments] for other requirements once the payment has been sent.
 	///
 	/// The builder will have the provided expiration set. Any changes to the expiration on the
-	/// returned builder will not be honored by [`ChannelManager`]. For `no-std`, the highest seen
+	/// returned builder will not be honored by [`ChannelManager`]. For non-`std`, the highest seen
 	/// block time minus two hours is used for the current time when determining if the refund has
 	/// expired.
 	///

lightning/src/ln/invoice_utils.rs

@@ -61,9 +61,8 @@ use core::iter::Iterator;
 /// [`ChannelManager::create_inbound_payment_for_hash`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment_for_hash
 /// [`PhantomRouteHints::channels`]: crate::ln::channelmanager::PhantomRouteHints::channels
 /// [`MIN_FINAL_CLTV_EXPIRY_DETLA`]: crate::ln::channelmanager::MIN_FINAL_CLTV_EXPIRY_DELTA
-///
-/// This can be used in a `no_std` environment, where [`std::time::SystemTime`] is not
-/// available and the current time is supplied by the caller.
+#[cfg_attr(feature = "std", doc = "")]
+#[cfg_attr(feature = "std", doc = "This can be used in a `no_std` environment, where [`std::time::SystemTime`] is not available and the current time is supplied by the caller.")]
 pub fn create_phantom_invoice<ES: Deref, NS: Deref, L: Deref>(
 	amt_msat: Option<u64>, payment_hash: Option<PaymentHash>, description: String,
 	invoice_expiry_delta_secs: u32, phantom_route_hints: Vec<PhantomRouteHints>, entropy_source: ES,
@@ -117,9 +116,8 @@ where
 /// [`ChannelManager::create_inbound_payment`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment
 /// [`ChannelManager::create_inbound_payment_for_hash`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment_for_hash
 /// [`PhantomRouteHints::channels`]: crate::ln::channelmanager::PhantomRouteHints::channels
-///
-/// This can be used in a `no_std` environment, where [`std::time::SystemTime`] is not
-/// available and the current time is supplied by the caller.
+#[cfg_attr(feature = "std", doc = "")]
+#[cfg_attr(feature = "std", doc = "This version can be used in a `no_std` environment, where [`std::time::SystemTime`] is not available and the current time is supplied by the caller.")]
 pub fn create_phantom_invoice_with_description_hash<ES: Deref, NS: Deref, L: Deref>(
 	amt_msat: Option<u64>, payment_hash: Option<PaymentHash>, invoice_expiry_delta_secs: u32,
 	description_hash: Sha256, phantom_route_hints: Vec<PhantomRouteHints>, entropy_source: ES,
@@ -399,9 +397,12 @@ where
 	)
 }
 
-/// See [`create_invoice_from_channelmanager_with_description_hash`]
-/// This version can be used in a `no_std` environment, where [`std::time::SystemTime`] is not
-/// available and the current time is supplied by the caller.
+/// Utility to construct an invoice. Generally, unless you want to do something like a custom
+/// `cltv_expiry`, this is what you should be using to create an invoice.
+#[cfg_attr(feature = "std", doc = "")]
+#[cfg_attr(feature = "std", doc = "See [`create_invoice_from_channelmanager_with_description_hash`] for more information.")]
+#[cfg_attr(feature = "std", doc = "")]
+#[cfg_attr(feature = "std", doc = "This can be used in a `no_std` environment, where [`std::time::SystemTime`] is not available and the current time is supplied by the caller.")]
 pub fn create_invoice_from_channelmanager_with_description_hash_and_duration_since_epoch<M: Deref, T: Deref, ES: Deref, NS: Deref, SP: Deref, F: Deref, R: Deref, L: Deref>(
 	channelmanager: &ChannelManager<M, T, ES, NS, SP, F, R, L>, node_signer: NS, logger: L,
 	network: Currency, amt_msat: Option<u64>, description_hash: Sha256,
@@ -424,9 +425,12 @@ pub fn create_invoice_from_channelmanager_with_description_hash_and_duration_sin
 	)
 }
 
-/// See [`create_invoice_from_channelmanager`]
-/// This version can be used in a `no_std` environment, where [`std::time::SystemTime`] is not
-/// available and the current time is supplied by the caller.
+/// Utility to construct an invoice. Generally, unless you want to do something like a custom
+/// `cltv_expiry`, this is what you should be using to create an invoice.
+#[cfg_attr(feature = "std", doc = "")]
+#[cfg_attr(feature = "std", doc = "See [`create_invoice_from_channelmanager`] for more information.")]
+#[cfg_attr(feature = "std", doc = "")]
+#[cfg_attr(feature = "std", doc = "This version can be used in a `no_std` environment, where [`std::time::SystemTime`] is not available and the current time is supplied by the caller.")]
 pub fn create_invoice_from_channelmanager_and_duration_since_epoch<M: Deref, T: Deref, ES: Deref, NS: Deref, SP: Deref, F: Deref, R: Deref, L: Deref>(
 	channelmanager: &ChannelManager<M, T, ES, NS, SP, F, R, L>, node_signer: NS, logger: L,
 	network: Currency, amt_msat: Option<u64>, description: String, duration_since_epoch: Duration,

lightning/src/ln/msgs.rs

@@ -87,7 +87,7 @@ pub enum DecodeError {
 	ShortRead,
 	/// A length descriptor in the packet didn't describe the later data correctly.
 	BadLengthDescriptor,
-	/// Error from [`std::io`].
+	/// Error from [`crate::io`].
 	Io(io::ErrorKind),
 	/// The message included zlib-compressed values, which we don't support.
 	UnsupportedCompression,

lightning/src/ln/outbound_payment.rs

@@ -438,8 +438,9 @@ impl_writeable_tlv_based_enum_legacy!(StaleExpiration,
 /// [`Event::PaymentFailed`]: crate::events::Event::PaymentFailed
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum RetryableSendFailure {
-	/// The provided [`PaymentParameters::expiry_time`] indicated that the payment has expired. Note
-	/// that this error is *not* caused by [`Retry::Timeout`].
+	/// The provided [`PaymentParameters::expiry_time`] indicated that the payment has expired.
+	#[cfg_attr(feature = "std", doc = "")]
+	#[cfg_attr(feature = "std", doc = "Note that this error is *not* caused by [`Retry::Timeout`].")]
 	///
 	/// [`PaymentParameters::expiry_time`]: crate::routing::router::PaymentParameters::expiry_time
 	PaymentExpired,

lightning/src/offers/invoice_macros.rs

@@ -16,7 +16,7 @@ macro_rules! invoice_builder_methods_common { (
 	#[doc = concat!("Sets the [`", stringify!($invoice_type), "::relative_expiry`]")]
 	#[doc = concat!("as seconds since [`", stringify!($invoice_type), "::created_at`].")]
 	#[doc = "Any expiry that has already passed is valid and can be checked for using"]
-	#[doc = concat!("[`", stringify!($invoice_type), "::is_expired`].")]
+	#[cfg_attr(feature = "std", doc = concat!("[`", stringify!($invoice_type), "::is_expired`]."))]
 	///
 	/// Successive calls to this method will override the previous setting.
 	pub fn relative_expiry($($self_mut)* $self: $self_type, relative_expiry_secs: u32) -> $return_type {