[INFO] fetching crate graph-similarity-cmd 0.0.1...
[INFO] checking graph-similarity-cmd-0.0.1 against master#c1feb3eceef7d5f0126c309a87062cf413fe0a25 for pr-121053
[INFO] extracting crate graph-similarity-cmd 0.0.1 into /workspace/builds/worker-7-tc1/source
[INFO] validating manifest of crates.io crate graph-similarity-cmd 0.0.1 on toolchain c1feb3eceef7d5f0126c309a87062cf413fe0a25
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+c1feb3eceef7d5f0126c309a87062cf413fe0a25" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] finished tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] tweaked toml for crates.io crate graph-similarity-cmd 0.0.1 written to /workspace/builds/worker-7-tc1/source/Cargo.toml
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+c1feb3eceef7d5f0126c309a87062cf413fe0a25" "generate-lockfile" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Updating crates.io index
[INFO] [stderr]      Locking 28 packages to latest compatible versions
[INFO] [stderr]       Adding closed01 v0.4.0 (latest: v0.5.0)
[INFO] [stderr]       Adding fixedbitset v0.1.9 (latest: v0.5.7)
[INFO] [stderr]       Adding graph-io-gml v0.1.1 (latest: v0.3.0)
[INFO] [stderr]       Adding graph-neighbor-matching v0.6.2 (latest: v0.9.0)
[INFO] [stderr]       Adding munkres v0.3.0 (latest: v0.5.2)
[INFO] [stderr]       Adding nalgebra v0.5.1 (latest: v0.32.5)
[INFO] [stderr]       Adding num v0.1.42 (latest: v0.4.2)
[INFO] [stderr]       Adding num-bigint v0.1.44 (latest: v0.4.4)
[INFO] [stderr]       Adding num-complex v0.1.43 (latest: v0.4.5)
[INFO] [stderr]       Adding num-rational v0.1.42 (latest: v0.4.1)
[INFO] [stderr]       Adding petgraph v0.2.10 (latest: v0.6.4)
[INFO] [stderr]       Adding rand v0.3.23 (latest: v0.8.5)
[INFO] [stderr]       Adding rand v0.4.6 (latest: v0.8.5)
[INFO] [stderr]       Adding rand_core v0.3.1 (latest: v0.6.4)
[INFO] [stderr]       Adding rand_core v0.4.2 (latest: v0.6.4)
[INFO] [stderr]       Adding rdrand v0.4.0 (latest: v0.8.3)
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+c1feb3eceef7d5f0126c309a87062cf413fe0a25" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr]   Downloaded petgraph v0.2.10
[INFO] [stderr]   Downloaded fixedbitset v0.1.9
[INFO] [stderr]   Downloaded closed01 v0.4.0
[INFO] [stderr]   Downloaded munkres v0.3.0
[INFO] [stderr]   Downloaded num-rational v0.1.42
[INFO] [stderr]   Downloaded num v0.1.42
[INFO] [stderr]   Downloaded num-bigint v0.1.44
[INFO] [stderr]   Downloaded nalgebra v0.5.1
[INFO] [stderr] error: failed to parse manifest at `/workspace/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/nalgebra-0.5.1/Cargo.toml`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   dependency (quickcheck) specified without providing a local path, Git repository, version, or workspace dependency to use
[ERROR] this task or one of its parent failed!
[ERROR] command failed: exit status: 101
[ERROR] note: run with `RUST_BACKTRACE=1` to display a backtrace.
[INFO] checking graph-similarity-cmd-0.0.1 against try#0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5 for pr-121053
[INFO] extracting crate graph-similarity-cmd 0.0.1 into /workspace/builds/worker-7-tc2/source
[INFO] validating manifest of crates.io crate graph-similarity-cmd 0.0.1 on toolchain 0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] finished tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] tweaked toml for crates.io crate graph-similarity-cmd 0.0.1 written to /workspace/builds/worker-7-tc2/source/Cargo.toml
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "generate-lockfile" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Updating crates.io index
[INFO] [stderr]      Locking 28 packages to latest compatible versions
[INFO] [stderr]       Adding closed01 v0.4.0 (latest: v0.5.0)
[INFO] [stderr]       Adding fixedbitset v0.1.9 (latest: v0.5.7)
[INFO] [stderr]       Adding graph-io-gml v0.1.1 (latest: v0.3.0)
[INFO] [stderr]       Adding graph-neighbor-matching v0.6.2 (latest: v0.9.0)
[INFO] [stderr]       Adding munkres v0.3.0 (latest: v0.5.2)
[INFO] [stderr]       Adding nalgebra v0.5.1 (latest: v0.32.5)
[INFO] [stderr]       Adding num v0.1.42 (latest: v0.4.2)
[INFO] [stderr]       Adding num-bigint v0.1.44 (latest: v0.4.4)
[INFO] [stderr]       Adding num-complex v0.1.43 (latest: v0.4.5)
[INFO] [stderr]       Adding num-rational v0.1.42 (latest: v0.4.1)
[INFO] [stderr]       Adding petgraph v0.2.10 (latest: v0.6.4)
[INFO] [stderr]       Adding rand v0.3.23 (latest: v0.8.5)
[INFO] [stderr]       Adding rand v0.4.6 (latest: v0.8.5)
[INFO] [stderr]       Adding rand_core v0.3.1 (latest: v0.6.4)
[INFO] [stderr]       Adding rand_core v0.4.2 (latest: v0.6.4)
[INFO] [stderr]       Adding rdrand v0.4.0 (latest: v0.8.3)
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr] error: failed to download `nalgebra v0.5.1`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   unable to get packages from source
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   failed to parse manifest at `/workspace/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/nalgebra-0.5.1/Cargo.toml`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   dependency (quickcheck) specified without providing a local path, Git repository, version, or workspace dependency to use
[INFO] checking graph-similarity-cmd-0.0.1 against try#0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5 for pr-121053
[INFO] extracting crate graph-similarity-cmd 0.0.1 into /workspace/builds/worker-7-tc2/source
[INFO] validating manifest of crates.io crate graph-similarity-cmd 0.0.1 on toolchain 0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] finished tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] tweaked toml for crates.io crate graph-similarity-cmd 0.0.1 written to /workspace/builds/worker-7-tc2/source/Cargo.toml
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "generate-lockfile" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Updating crates.io index
[INFO] [stderr]      Locking 28 packages to latest compatible versions
[INFO] [stderr]       Adding closed01 v0.4.0 (latest: v0.5.0)
[INFO] [stderr]       Adding fixedbitset v0.1.9 (latest: v0.5.7)
[INFO] [stderr]       Adding graph-io-gml v0.1.1 (latest: v0.3.0)
[INFO] [stderr]       Adding graph-neighbor-matching v0.6.2 (latest: v0.9.0)
[INFO] [stderr]       Adding munkres v0.3.0 (latest: v0.5.2)
[INFO] [stderr]       Adding nalgebra v0.5.1 (latest: v0.32.5)
[INFO] [stderr]       Adding num v0.1.42 (latest: v0.4.2)
[INFO] [stderr]       Adding num-bigint v0.1.44 (latest: v0.4.4)
[INFO] [stderr]       Adding num-complex v0.1.43 (latest: v0.4.5)
[INFO] [stderr]       Adding num-rational v0.1.42 (latest: v0.4.1)
[INFO] [stderr]       Adding petgraph v0.2.10 (latest: v0.6.4)
[INFO] [stderr]       Adding rand v0.3.23 (latest: v0.8.5)
[INFO] [stderr]       Adding rand v0.4.6 (latest: v0.8.5)
[INFO] [stderr]       Adding rand_core v0.3.1 (latest: v0.6.4)
[INFO] [stderr]       Adding rand_core v0.4.2 (latest: v0.6.4)
[INFO] [stderr]       Adding rdrand v0.4.0 (latest: v0.8.3)
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr] error: failed to download `nalgebra v0.5.1`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   unable to get packages from source
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   failed to parse manifest at `/workspace/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/nalgebra-0.5.1/Cargo.toml`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   dependency (quickcheck) specified without providing a local path, Git repository, version, or workspace dependency to use
[INFO] checking graph-similarity-cmd-0.0.1 against try#0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5 for pr-121053
[INFO] extracting crate graph-similarity-cmd 0.0.1 into /workspace/builds/worker-7-tc2/source
[INFO] validating manifest of crates.io crate graph-similarity-cmd 0.0.1 on toolchain 0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] finished tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] tweaked toml for crates.io crate graph-similarity-cmd 0.0.1 written to /workspace/builds/worker-7-tc2/source/Cargo.toml
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "generate-lockfile" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Updating crates.io index
[INFO] [stderr]      Locking 28 packages to latest compatible versions
[INFO] [stderr]       Adding closed01 v0.4.0 (latest: v0.5.0)
[INFO] [stderr]       Adding fixedbitset v0.1.9 (latest: v0.5.7)
[INFO] [stderr]       Adding graph-io-gml v0.1.1 (latest: v0.3.0)
[INFO] [stderr]       Adding graph-neighbor-matching v0.6.2 (latest: v0.9.0)
[INFO] [stderr]       Adding munkres v0.3.0 (latest: v0.5.2)
[INFO] [stderr]       Adding nalgebra v0.5.1 (latest: v0.32.5)
[INFO] [stderr]       Adding num v0.1.42 (latest: v0.4.2)
[INFO] [stderr]       Adding num-bigint v0.1.44 (latest: v0.4.4)
[INFO] [stderr]       Adding num-complex v0.1.43 (latest: v0.4.5)
[INFO] [stderr]       Adding num-rational v0.1.42 (latest: v0.4.1)
[INFO] [stderr]       Adding petgraph v0.2.10 (latest: v0.6.4)
[INFO] [stderr]       Adding rand v0.3.23 (latest: v0.8.5)
[INFO] [stderr]       Adding rand v0.4.6 (latest: v0.8.5)
[INFO] [stderr]       Adding rand_core v0.3.1 (latest: v0.6.4)
[INFO] [stderr]       Adding rand_core v0.4.2 (latest: v0.6.4)
[INFO] [stderr]       Adding rdrand v0.4.0 (latest: v0.8.3)
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr] error: failed to download `nalgebra v0.5.1`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   unable to get packages from source
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   failed to parse manifest at `/workspace/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/nalgebra-0.5.1/Cargo.toml`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   dependency (quickcheck) specified without providing a local path, Git repository, version, or workspace dependency to use
[INFO] checking graph-similarity-cmd-0.0.1 against try#0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5 for pr-121053
[INFO] extracting crate graph-similarity-cmd 0.0.1 into /workspace/builds/worker-7-tc2/source
[INFO] validating manifest of crates.io crate graph-similarity-cmd 0.0.1 on toolchain 0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] finished tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] tweaked toml for crates.io crate graph-similarity-cmd 0.0.1 written to /workspace/builds/worker-7-tc2/source/Cargo.toml
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "generate-lockfile" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Updating crates.io index
[INFO] [stderr]      Locking 28 packages to latest compatible versions
[INFO] [stderr]       Adding closed01 v0.4.0 (latest: v0.5.0)
[INFO] [stderr]       Adding fixedbitset v0.1.9 (latest: v0.5.7)
[INFO] [stderr]       Adding graph-io-gml v0.1.1 (latest: v0.3.0)
[INFO] [stderr]       Adding graph-neighbor-matching v0.6.2 (latest: v0.9.0)
[INFO] [stderr]       Adding munkres v0.3.0 (latest: v0.5.2)
[INFO] [stderr]       Adding nalgebra v0.5.1 (latest: v0.32.5)
[INFO] [stderr]       Adding num v0.1.42 (latest: v0.4.2)
[INFO] [stderr]       Adding num-bigint v0.1.44 (latest: v0.4.4)
[INFO] [stderr]       Adding num-complex v0.1.43 (latest: v0.4.5)
[INFO] [stderr]       Adding num-rational v0.1.42 (latest: v0.4.1)
[INFO] [stderr]       Adding petgraph v0.2.10 (latest: v0.6.4)
[INFO] [stderr]       Adding rand v0.3.23 (latest: v0.8.5)
[INFO] [stderr]       Adding rand v0.4.6 (latest: v0.8.5)
[INFO] [stderr]       Adding rand_core v0.3.1 (latest: v0.6.4)
[INFO] [stderr]       Adding rand_core v0.4.2 (latest: v0.6.4)
[INFO] [stderr]       Adding rdrand v0.4.0 (latest: v0.8.3)
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr] error: failed to download `nalgebra v0.5.1`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   unable to get packages from source
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   failed to parse manifest at `/workspace/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/nalgebra-0.5.1/Cargo.toml`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   dependency (quickcheck) specified without providing a local path, Git repository, version, or workspace dependency to use
[INFO] checking graph-similarity-cmd-0.0.1 against try#0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5 for pr-121053
[INFO] extracting crate graph-similarity-cmd 0.0.1 into /workspace/builds/worker-7-tc2/source
[INFO] validating manifest of crates.io crate graph-similarity-cmd 0.0.1 on toolchain 0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] finished tweaking crates.io crate graph-similarity-cmd 0.0.1
[INFO] tweaked toml for crates.io crate graph-similarity-cmd 0.0.1 written to /workspace/builds/worker-7-tc2/source/Cargo.toml
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "generate-lockfile" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Updating crates.io index
[INFO] [stderr]      Locking 28 packages to latest compatible versions
[INFO] [stderr]       Adding closed01 v0.4.0 (latest: v0.5.0)
[INFO] [stderr]       Adding fixedbitset v0.1.9 (latest: v0.5.7)
[INFO] [stderr]       Adding graph-io-gml v0.1.1 (latest: v0.3.0)
[INFO] [stderr]       Adding graph-neighbor-matching v0.6.2 (latest: v0.9.0)
[INFO] [stderr]       Adding munkres v0.3.0 (latest: v0.5.2)
[INFO] [stderr]       Adding nalgebra v0.5.1 (latest: v0.32.5)
[INFO] [stderr]       Adding num v0.1.42 (latest: v0.4.2)
[INFO] [stderr]       Adding num-bigint v0.1.44 (latest: v0.4.4)
[INFO] [stderr]       Adding num-complex v0.1.43 (latest: v0.4.5)
[INFO] [stderr]       Adding num-rational v0.1.42 (latest: v0.4.1)
[INFO] [stderr]       Adding petgraph v0.2.10 (latest: v0.6.4)
[INFO] [stderr]       Adding rand v0.3.23 (latest: v0.8.5)
[INFO] [stderr]       Adding rand v0.4.6 (latest: v0.8.5)
[INFO] [stderr]       Adding rand_core v0.3.1 (latest: v0.6.4)
[INFO] [stderr]       Adding rand_core v0.4.2 (latest: v0.6.4)
[INFO] [stderr]       Adding rdrand v0.4.0 (latest: v0.8.3)
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+0d3c0c4551bd9d6b6a4bd51e251b596e0195adf5" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr] error: failed to download `nalgebra v0.5.1`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   unable to get packages from source
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   failed to parse manifest at `/workspace/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/nalgebra-0.5.1/Cargo.toml`
[INFO] [stderr] 
[INFO] [stderr] Caused by:
[INFO] [stderr]   dependency (quickcheck) specified without providing a local path, Git repository, version, or workspace dependency to use
[ERROR] this task or one of its parent failed!
[ERROR] command failed: exit status: 101
[ERROR] note: run with `RUST_BACKTRACE=1` to display a backtrace.