Run with mutagen on travis.

Sadly our test coverage isn't very good and I had to hunt for
functions to mutate where we fail tests on every mutation mutagen
creates, but committing the framework is a start.

.travis.yml

@@ -1,7 +1,7 @@
 language: rust
 rust:
   - stable
-  - beta
+  - nightly
   - 1.22.0
   - 1.34.2
 cache: cargo
@@ -22,6 +22,14 @@ script:
      - if [ "$(rustup show | grep default | grep 1.22.0)" != "" ]; then RUSTFLAGS="-C link-dead-code" cargo test --verbose -p lightning; fi
      # Run lightning workspace fuzz tests for Rust 1.34.2
      - if [ "$(rustup show | grep default | grep 1.34.2)" != "" ]; then cd fuzz && cargo test --verbose && ./travis-fuzz.sh; fi
+     # Run mutagen on nightly with TheBlueMatt's fork which just sets an extra features flag and
+     # exits with non-0 status if any mutations resulted in anything except test failures.
+     - if [ "$(rustup show | grep default | grep nightly)" != "" ]; then
+           rm -rf mutagen && git clone https://github.com/TheBlueMatt/mutagen &&
+           cargo install --force --path mutagen/mutagen-runner &&
+           cd lightning &&
+           cargo mutagen; fi
+     # Generate codecov on stable
      - if [ "$(rustup show | grep default | grep stable)" != "" ]; then
            wget https://github.com/SimonKagstrom/kcov/archive/master.tar.gz &&
            tar xzf master.tar.gz &&

lightning/Cargo.toml

@@ -13,18 +13,22 @@ Still missing tons of error-handling. See GitHub issues for suggested projects i
 [features]
 # Supports tracking channels with a non-bitcoin chain hashes. Currently enables all kinds of fun DoS attacks.
 non_bitcoin_chain_hash_routing = []
-fuzztarget = ["secp256k1/fuzztarget", "bitcoin/fuzztarget", "bitcoin_hashes/fuzztarget"]
 # Unlog messages superior at targeted level.
 max_level_off = []
 max_level_error = []
 max_level_warn = []
 max_level_info = []
 max_level_debug = []
 
+# Testing only features, don't enable these unless you want to run rust-lightning tests!
+fuzztarget = ["secp256k1/fuzztarget", "bitcoin/fuzztarget", "bitcoin_hashes/fuzztarget"]
+mutation_testing = ["mutagen"]
+
 [dependencies]
 bitcoin = "0.21"
 bitcoin_hashes = "0.7"
 secp256k1 = "0.15"
+mutagen = { git = "https://github.com/TheBlueMatt/mutagen", optional = true }
 
 [dev-dependencies.bitcoin]
 version = "0.21"

lightning/src/lib.rs

@@ -23,8 +23,15 @@ extern crate bitcoin_hashes;
 extern crate secp256k1;
 #[cfg(test)] extern crate rand;
 #[cfg(test)] extern crate hex;
+#[cfg(all(test, feature = "mutation_testing"))] extern crate mutagen;
 
 #[macro_use]
 pub mod util;
 pub mod chain;
 pub mod ln;
+
+#[cfg(all(
+		any(feature = "mutation_testing", feature = "fuzztarget"),
+		not(any(test, debug_assertions))
+		))]
+const ERR: () = "You should never be building with feature = mutation_testing or feature = fuzztarget! They are used to compile with broken code for testing only!";

lightning/src/ln/channel.rs

@@ -36,6 +36,9 @@ use std::default::Default;
 use std::{cmp,mem,fmt};
 use std::sync::{Arc};
 
+#[cfg(all(test, feature = "mutation_testing"))]
+use mutagen::mutate;
+
 #[cfg(test)]
 pub struct ChannelValueStat {
 	pub value_to_self_msat: u64,
@@ -2337,6 +2340,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 		Ok(())
 	}
 
+	#[cfg_attr(all(test, feature = "mutation_testing"), mutate)]
 	fn get_last_revoke_and_ack(&self) -> msgs::RevokeAndACK {
 		let next_per_commitment_point = PublicKey::from_secret_key(&self.secp_ctx, &self.build_local_commitment_secret(self.cur_local_commitment_transaction_number));
 		let per_commitment_secret = chan_utils::build_commitment_secret(self.local_keys.commitment_seed(), self.cur_local_commitment_transaction_number + 2);