[INFO] fetching crate chain-p2p 0.1.7... [INFO] checking chain-p2p-0.1.7 against try#4d98531622e1718ae0bc3c7a1ab9cd8938428452+rustflags=-Dtail_expr_drop_order for pr-129604 [INFO] extracting crate chain-p2p 0.1.7 into /workspace/builds/worker-0-tc2/source [INFO] validating manifest of crates.io crate chain-p2p 0.1.7 on toolchain 4d98531622e1718ae0bc3c7a1ab9cd8938428452 [INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+4d98531622e1718ae0bc3c7a1ab9cd8938428452" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }` [INFO] started tweaking crates.io crate chain-p2p 0.1.7 [INFO] finished tweaking crates.io crate chain-p2p 0.1.7 [INFO] tweaked toml for crates.io crate chain-p2p 0.1.7 written to /workspace/builds/worker-0-tc2/source/Cargo.toml [INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+4d98531622e1718ae0bc3c7a1ab9cd8938428452" "generate-lockfile" "--manifest-path" "Cargo.toml", kill_on_drop: false }` [INFO] [stderr] Blocking waiting for file lock on package cache [INFO] [stderr] Updating crates.io index [INFO] [stderr] Blocking waiting for file lock on package cache [INFO] [stderr] Locking 61 packages to latest compatible versions [INFO] [stderr] Adding bitflags v1.3.2 (latest: v2.6.0) [INFO] [stderr] Adding byteorder v0.3.13 (latest: v1.5.0) [INFO] [stderr] Adding bytes v0.4.12 (latest: v1.7.1) [INFO] [stderr] Adding cfg-if v0.1.10 (latest: v1.0.0) [INFO] [stderr] Adding cloudabi v0.0.3 (latest: v0.1.0) [INFO] [stderr] Adding crossbeam-deque v0.7.4 (latest: v0.8.5) [INFO] [stderr] Adding crossbeam-epoch v0.8.2 (latest: v0.9.18) [INFO] [stderr] Adding crossbeam-queue v0.2.3 (latest: v0.3.11) [INFO] [stderr] Adding crossbeam-utils v0.7.2 (latest: v0.8.20) [INFO] [stderr] Adding futures v0.1.31 (latest: v0.3.30) [INFO] [stderr] Adding hermit-abi v0.3.9 (latest: v0.4.0) [INFO] [stderr] Adding lock_api v0.3.4 (latest: v0.4.12) [INFO] [stderr] Adding log v0.3.9 (latest: v0.4.22) [INFO] [stderr] Adding memoffset v0.5.6 (latest: v0.9.1) [INFO] [stderr] Adding mio v0.6.23 (latest: v1.0.2) [INFO] [stderr] Adding miow v0.2.2 (latest: v0.6.0) [INFO] [stderr] Adding parking_lot v0.9.0 (latest: v0.12.3) [INFO] [stderr] Adding parking_lot_core v0.6.3 (latest: v0.9.10) [INFO] [stderr] Adding redox_syscall v0.1.57 (latest: v0.5.3) [INFO] [stderr] Adding rustc_version v0.2.3 (latest: v0.4.1) [INFO] [stderr] Adding scoped-tls v0.1.2 (latest: v1.0.1) [INFO] [stderr] Adding semver v0.9.0 (latest: v1.0.23) [INFO] [stderr] Adding semver-parser v0.7.0 (latest: v0.10.2) [INFO] [stderr] Adding smallvec v0.6.14 (latest: v1.13.2) [INFO] [stderr] Adding tokio v0.1.22 (latest: v1.40.0) [INFO] [stderr] Adding winapi v0.2.8 (latest: v0.3.9) [INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+4d98531622e1718ae0bc3c7a1ab9cd8938428452" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }` [INFO] [stderr] warning: no edition set: defaulting to the 2015 edition while the latest is 2021 [INFO] [stderr] Blocking waiting for file lock on package cache [INFO] [stderr] Blocking waiting for file lock on package cache [INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:923055f121b5182466d55868a8b05e67af8ba4a3a3f6bad814e953ca3cd3ac2a" "/opt/rustwide/cargo-home/bin/cargo" "+4d98531622e1718ae0bc3c7a1ab9cd8938428452" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }` [INFO] [stdout] 28fc394910cf219b97eb0591da645d5149f9f9ab21d93eee458c26d79d71fffd [INFO] running `Command { std: "docker" "start" "-a" "28fc394910cf219b97eb0591da645d5149f9f9ab21d93eee458c26d79d71fffd", kill_on_drop: false }` [INFO] running `Command { std: "docker" "inspect" "28fc394910cf219b97eb0591da645d5149f9f9ab21d93eee458c26d79d71fffd", kill_on_drop: false }` [INFO] running `Command { std: "docker" "rm" "-f" "28fc394910cf219b97eb0591da645d5149f9f9ab21d93eee458c26d79d71fffd", kill_on_drop: false }` [INFO] [stdout] 28fc394910cf219b97eb0591da645d5149f9f9ab21d93eee458c26d79d71fffd [INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc2/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_INCREMENTAL=0" "-e" "RUST_BACKTRACE=full" "-e" "RUSTFLAGS=--cap-lints=forbid -Dtail_expr_drop_order" "-e" "RUSTDOCFLAGS=--cap-lints=forbid" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "ghcr.io/rust-lang/crates-build-env/linux@sha256:923055f121b5182466d55868a8b05e67af8ba4a3a3f6bad814e953ca3cd3ac2a" "/opt/rustwide/cargo-home/bin/cargo" "+4d98531622e1718ae0bc3c7a1ab9cd8938428452" "check" "--frozen" "--all" "--all-targets" "--message-format=json", kill_on_drop: false }` [INFO] [stdout] f567024405d9440df47d3f97710473d4406a33333645263846caa6326025b25b [INFO] running `Command { std: "docker" "start" "-a" "f567024405d9440df47d3f97710473d4406a33333645263846caa6326025b25b", kill_on_drop: false }` [INFO] [stderr] warning: no edition set: defaulting to the 2015 edition while the latest is 2021 [INFO] [stderr] Checking cfg-if v0.1.10 [INFO] [stderr] Compiling crossbeam-utils v0.7.2 [INFO] [stderr] Compiling maybe-uninit v2.0.0 [INFO] [stderr] Checking futures v0.1.31 [INFO] [stderr] Checking byteorder v1.5.0 [INFO] [stderr] Compiling memoffset v0.5.6 [INFO] [stderr] Compiling crossbeam-epoch v0.8.2 [INFO] [stderr] Checking scoped-tls v0.1.2 [INFO] [stderr] Checking byteorder v0.3.13 [INFO] [stderr] Checking lock_api v0.3.4 [INFO] [stderr] Checking log v0.3.9 [INFO] [stderr] Checking iovec v0.1.4 [INFO] [stderr] Checking num_cpus v1.16.0 [INFO] [stderr] Compiling parking_lot_core v0.6.3 [INFO] [stderr] Compiling parking_lot v0.9.0 [INFO] [stderr] Checking net2 v0.2.39 [INFO] [stderr] Checking bytes v0.4.12 [INFO] [stderr] Checking smallvec v0.6.14 [INFO] [stderr] Checking mio v0.6.23 [INFO] [stderr] Checking crossbeam-queue v0.2.3 [INFO] [stderr] Checking tokio-executor v0.1.10 [INFO] [stderr] Checking tokio-io v0.1.13 [INFO] [stderr] Checking tokio-sync v0.1.8 [INFO] [stderr] Checking mio-uds v0.6.8 [INFO] [stderr] Checking crossbeam-deque v0.7.4 [INFO] [stderr] Checking tokio-timer v0.2.13 [INFO] [stderr] Checking tokio-current-thread v0.1.7 [INFO] [stderr] Checking tokio-threadpool v0.1.18 [INFO] [stderr] Checking tokio-codec v0.1.2 [INFO] [stderr] Checking tokio-reactor v0.1.12 [INFO] [stderr] Checking tokio-udp v0.1.6 [INFO] [stderr] Checking tokio-uds v0.2.7 [INFO] [stderr] Checking tokio-tcp v0.1.4 [INFO] [stderr] Checking tokio-fs v0.1.7 [INFO] [stderr] Checking tokio v0.1.22 [INFO] [stderr] Checking tokio-core v0.1.18 [INFO] [stderr] Checking chain-p2p v0.1.7 (/opt/rustwide/workdir) [INFO] [stdout] warning: field `capacity` is never read [INFO] [stdout] --> src/p2p/mod.rs:21:5 [INFO] [stdout] | [INFO] [stdout] 19 | pub struct P2PManager { [INFO] [stdout] | ---------- field in this struct [INFO] [stdout] 20 | conns: Arc>, [INFO] [stdout] 21 | capacity: usize, [INFO] [stdout] | ^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = note: `P2PManager` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis [INFO] [stdout] = note: `#[warn(dead_code)]` on by default [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] warning: field `addr` is never read [INFO] [stdout] --> src/p2p/client.rs:41:5 [INFO] [stdout] | [INFO] [stdout] 34 | pub struct Session { [INFO] [stdout] | ------- field in this struct [INFO] [stdout] ... [INFO] [stdout] 41 | addr: SocketAddr, [INFO] [stdout] | ^^^^ [INFO] [stdout] | [INFO] [stdout] = note: `Session` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021 [INFO] [stdout] --> src/p2p/mod.rs:33:20 [INFO] [stdout] | [INFO] [stdout] 28 | let mut sessions = Vec::new(); [INFO] [stdout] | -------- these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] ... [INFO] [stdout] 33 | conns: Arc::new(Mutex::new(Conns::new(cap))), [INFO] [stdout] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = warning: this changes meaning in Rust 2024 [INFO] [stdout] = note: for more information, see issue #123739 [INFO] [stdout] = note: requested on the command line with `-D tail-expr-drop-order` [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] warning: unused `Result` that must be used [INFO] [stdout] --> src/p2p/mod.rs:112:9 [INFO] [stdout] | [INFO] [stdout] 112 | Conns::update(conns_update, index, conn_addr); [INFO] [stdout] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = note: this `Result` may be an `Err` variant, which should be handled [INFO] [stdout] = note: `#[warn(unused_must_use)]` on by default [INFO] [stdout] help: use `let _ = ...` to ignore the resulting value [INFO] [stdout] | [INFO] [stdout] 112 | let _ = Conns::update(conns_update, index, conn_addr); [INFO] [stdout] | +++++++ [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] warning: unused `Result` that must be used [INFO] [stdout] --> src/p2p/mod.rs:123:9 [INFO] [stdout] | [INFO] [stdout] 123 | Conns::remove(conns_dis, index); [INFO] [stdout] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = note: this `Result` may be an `Err` variant, which should be handled [INFO] [stdout] help: use `let _ = ...` to ignore the resulting value [INFO] [stdout] | [INFO] [stdout] 123 | let _ = Conns::remove(conns_dis, index); [INFO] [stdout] | +++++++ [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021 [INFO] [stdout] --> src/p2p/mod.rs:177:9 [INFO] [stdout] | [INFO] [stdout] 175 | let manager = self.sessions.swap_remove(index); [INFO] [stdout] | ------- these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 176 | [INFO] [stdout] 177 | manager.unwrap().shutdown() [INFO] [stdout] | ^^^^^^^^^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = warning: this changes meaning in Rust 2024 [INFO] [stdout] = note: for more information, see issue #123739 [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021 [INFO] [stdout] --> src/p2p/server.rs:271:22 [INFO] [stdout] | [INFO] [stdout] 257 | let sender_clone = conn.sender.clone(); [INFO] [stdout] | ------------ these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 258 | let iter_recv = stream::iter_ok::<_, Error>(iter::repeat(())); [INFO] [stdout] 259 | let amt_read = iter_recv.fold(reader, move |reader, _| { [INFO] [stdout] | ------ these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 260 | let msg = vec![0u8;1024]; [INFO] [stdout] 261 | let recv = tokio_io::io::read(reader, msg); [INFO] [stdout] | ---- these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 262 | let recv= recv.and_then(|(reader, msg, pos)| { [INFO] [stdout] | ---- these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] ... [INFO] [stdout] 270 | let sender_clone_inner = sender_clone.clone(); [INFO] [stdout] | ------------------ these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 271 | recv.map(move |(reader, mut message, pos)| { [INFO] [stdout] | ______________________^ [INFO] [stdout] 272 | | // println!("server 已经读了 {} bytes", pos); [INFO] [stdout] 273 | | // println!("bytes is {:?}", message); [INFO] [stdout] 274 | | message.reverse(); [INFO] [stdout] ... | [INFO] [stdout] 280 | | reader [INFO] [stdout] 281 | | }) [INFO] [stdout] | |_____________^ [INFO] [stdout] | [INFO] [stdout] = warning: this changes meaning in Rust 2024 [INFO] [stdout] = note: for more information, see issue #123739 [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] error: aborting due to 3 previous errors; 4 warnings emitted [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] warning: field `capacity` is never read [INFO] [stdout] --> src/p2p/mod.rs:21:5 [INFO] [stdout] | [INFO] [stdout] 19 | pub struct P2PManager { [INFO] [stdout] | ---------- field in this struct [INFO] [stdout] 20 | conns: Arc>, [INFO] [stdout] 21 | capacity: usize, [INFO] [stdout] | ^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = note: `P2PManager` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis [INFO] [stdout] = note: `#[warn(dead_code)]` on by default [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] warning: field `addr` is never read [INFO] [stdout] --> src/p2p/client.rs:41:5 [INFO] [stdout] | [INFO] [stdout] 34 | pub struct Session { [INFO] [stdout] | ------- field in this struct [INFO] [stdout] ... [INFO] [stdout] 41 | addr: SocketAddr, [INFO] [stdout] | ^^^^ [INFO] [stdout] | [INFO] [stdout] = note: `Session` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021 [INFO] [stdout] --> src/p2p/mod.rs:33:20 [INFO] [stdout] | [INFO] [stdout] 28 | let mut sessions = Vec::new(); [INFO] [stdout] | -------- these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] ... [INFO] [stdout] 33 | conns: Arc::new(Mutex::new(Conns::new(cap))), [INFO] [stdout] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = warning: this changes meaning in Rust 2024 [INFO] [stdout] = note: for more information, see issue #123739 [INFO] [stdout] = note: requested on the command line with `-D tail-expr-drop-order` [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] warning: unused `Result` that must be used [INFO] [stdout] --> src/p2p/mod.rs:112:9 [INFO] [stdout] | [INFO] [stdout] 112 | Conns::update(conns_update, index, conn_addr); [INFO] [stdout] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = note: this `Result` may be an `Err` variant, which should be handled [INFO] [stdout] = note: `#[warn(unused_must_use)]` on by default [INFO] [stdout] help: use `let _ = ...` to ignore the resulting value [INFO] [stdout] | [INFO] [stdout] 112 | let _ = Conns::update(conns_update, index, conn_addr); [INFO] [stdout] | +++++++ [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] warning: unused `Result` that must be used [INFO] [stdout] --> src/p2p/mod.rs:123:9 [INFO] [stdout] | [INFO] [stdout] 123 | Conns::remove(conns_dis, index); [INFO] [stdout] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = note: this `Result` may be an `Err` variant, which should be handled [INFO] [stdout] help: use `let _ = ...` to ignore the resulting value [INFO] [stdout] | [INFO] [stdout] 123 | let _ = Conns::remove(conns_dis, index); [INFO] [stdout] | +++++++ [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021 [INFO] [stdout] --> src/p2p/mod.rs:177:9 [INFO] [stdout] | [INFO] [stdout] 175 | let manager = self.sessions.swap_remove(index); [INFO] [stdout] | ------- these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 176 | [INFO] [stdout] 177 | manager.unwrap().shutdown() [INFO] [stdout] | ^^^^^^^^^^^^^^^^ [INFO] [stdout] | [INFO] [stdout] = warning: this changes meaning in Rust 2024 [INFO] [stdout] = note: for more information, see issue #123739 [INFO] [stdout] [INFO] [stdout] [INFO] [stdout] error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021 [INFO] [stdout] --> src/p2p/server.rs:271:22 [INFO] [stdout] | [INFO] [stdout] 257 | let sender_clone = conn.sender.clone(); [INFO] [stdout] | ------------ these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 258 | let iter_recv = stream::iter_ok::<_, Error>(iter::repeat(())); [INFO] [stdout] 259 | let amt_read = iter_recv.fold(reader, move |reader, _| { [INFO] [stdout] | ------ these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 260 | let msg = vec![0u8;1024]; [INFO] [stdout] 261 | let recv = tokio_io::io::read(reader, msg); [INFO] [stdout] | ---- these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 262 | let recv= recv.and_then(|(reader, msg, pos)| { [INFO] [stdout] | ---- these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] ... [INFO] [stdout] 270 | let sender_clone_inner = sender_clone.clone(); [INFO] [stdout] | ------------------ these values have significant drop implementation and will observe changes in drop order under Edition 2024 [INFO] [stdout] 271 | recv.map(move |(reader, mut message, pos)| { [INFO] [stdout] | ______________________^ [INFO] [stdout] 272 | | // println!("server 已经读了 {} bytes", pos); [INFO] [stdout] 273 | | // println!("bytes is {:?}", message); [INFO] [stdout] 274 | | message.reverse(); [INFO] [stdout] ... | [INFO] [stdout] 280 | | reader [INFO] [stdout] 281 | | }) [INFO] [stdout] | |_____________^ [INFO] [stdout] | [INFO] [stdout] = warning: this changes meaning in Rust 2024 [INFO] [stdout] = note: for more information, see issue #123739 [INFO] [stdout] [INFO] [stdout] [INFO] [stderr] error: could not compile `chain-p2p` (lib test) due to 4 previous errors; 4 warnings emitted [INFO] [stderr] warning: build failed, waiting for other jobs to finish... [INFO] [stdout] error: aborting due to 3 previous errors; 4 warnings emitted [INFO] [stdout] [INFO] [stdout] [INFO] [stderr] error: could not compile `chain-p2p` (lib) due to 4 previous errors; 4 warnings emitted [INFO] running `Command { std: "docker" "inspect" "f567024405d9440df47d3f97710473d4406a33333645263846caa6326025b25b", kill_on_drop: false }` [INFO] running `Command { std: "docker" "rm" "-f" "f567024405d9440df47d3f97710473d4406a33333645263846caa6326025b25b", kill_on_drop: false }` [INFO] [stdout] f567024405d9440df47d3f97710473d4406a33333645263846caa6326025b25b