thread 'main' panicked at 'attempt to subtract with overflow', offline-election/src/subcommands/staking.rs:344:22

[atorrente75]

Commit hash:

2dd3e622be6392d3e790faed8868293ac28fd77e

Command:

cargo run -- staking -i 10 -r

Output:

Finished dev [unoptimized + debuginfo] target(s) in 0.23s
Running /home/polkast/offline-phragmen/target/debug/offline-election staking -i 10 -r
[2020-07-10T23:03:37Z INFO ] program args: Opt { at: Some(0xddf3ed5fc4c8faa952f31a27d622bc91bef38590f4a0a965b3365032a267b181), uri: "ws://localhost:9944", network: "polkadot", verbosity: 0, cmd: Staking(StakingConfig { count: None, output: None, iterations: 10, reduce: true }) }
[2020-07-10T23:03:37Z INFO ] total_issuance = 8315411,309DOT (8,315,411,309,643,337,742)
[2020-07-10T23:03:51Z DEBUG] ⏳ data_scrape took 14772ms.
[2020-07-10T23:03:53Z DEBUG] ⏳ phragmen_run took 1378ms.
[2020-07-10T23:03:53Z DEBUG] ⏳ ratio_into_staked_run took 9ms.
[2020-07-10T23:03:53Z DEBUG] ⏳ build_support_map_run took 11ms.
[2020-07-10T23:03:54Z DEBUG] ⏳ equalize_post_processing took 929ms.
thread 'main' panicked at 'attempt to subtract with overflow', offline-election/src/subcommands/staking.rs:344:22
stack backtrace:
0: backtrace::backtrace::libunwind::trace
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
1: backtrace::backtrace::trace_unsynchronized
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
2: std::sys_common::backtrace::_print_fmt
at src/libstd/sys_common/backtrace.rs:78
3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
at src/libstd/sys_common/backtrace.rs:59
4: core::fmt::write
at src/libcore/fmt/mod.rs:1069
5: std::io::Write::write_fmt
at src/libstd/io/mod.rs:1504
6: std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:62
7: std::sys_common::backtrace::print
at src/libstd/sys_common/backtrace.rs:49
8: std::panicking::default_hook::{{closure}}
at src/libstd/panicking.rs:198
9: std::panicking::default_hook
at src/libstd/panicking.rs:218
10: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:511
11: rust_begin_unwind
at src/libstd/panicking.rs:419
12: core::panicking::panic_fmt
at src/libcore/panicking.rs:111
13: core::panicking::panic
at src/libcore/panicking.rs:54
14: offline_election::subcommands::staking::run::{{closure}}
at offline-election/src/subcommands/staking.rs:344
15: <core::future::from_generator::GenFuture as core::future::future::Future>::poll
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libcore/future/mod.rs:66
16: offline_election::main::main::{{closure}}
at offline-election/src/main.rs:248
17: <core::future::from_generator::GenFuture as core::future::future::Future>::poll
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libcore/future/mod.rs:66
18: offline_election::main::{{closure}}
at offline-election/src/main.rs:199
19: <core::future::from_generator::GenFuture as core::future::future::Future>::poll
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libcore/future/mod.rs:66
20: async_std::task::block_on::block_on::{{closure}}
at /home/polkast/.cargo/registry/src/github.com-1ecc6299db9ec823/async-std-1.5.0/src/task/block_on.rs:68
21: <core::future::from_generator::GenFuture as core::future::future::Future>::poll
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libcore/future/mod.rs:66
22: async_std::task::block_on::run::{{closure}}
at /home/polkast/.cargo/registry/src/github.com-1ecc6299db9ec823/async-std-1.5.0/src/task/block_on.rs:128
23: std::thread::local::LocalKey::try_with
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libstd/thread/local.rs:263
24: std::thread::local::LocalKey::with
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libstd/thread/local.rs:239
25: async_std::task::block_on::run
at /home/polkast/.cargo/registry/src/github.com-1ecc6299db9ec823/async-std-1.5.0/src/task/block_on.rs:118
26: async_std::task::block_on::block_on::{{closure}}
at /home/polkast/.cargo/registry/src/github.com-1ecc6299db9ec823/async-std-1.5.0/src/task/block_on.rs:72
27: async_std::task::task::Task::set_current::{{closure}}
at /home/polkast/.cargo/registry/src/github.com-1ecc6299db9ec823/async-std-1.5.0/src/task/task.rs:129
28: std::thread::local::LocalKey::try_with
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libstd/thread/local.rs:263
29: std::thread::local::LocalKey::with
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libstd/thread/local.rs:239
30: async_std::task::task::Task::set_current
at /home/polkast/.cargo/registry/src/github.com-1ecc6299db9ec823/async-std-1.5.0/src/task/task.rs:124
31: async_std::task::block_on::block_on
at /home/polkast/.cargo/registry/src/github.com-1ecc6299db9ec823/async-std-1.5.0/src/task/block_on.rs:72
32: offline_election::main
at offline-election/src/main.rs:199
33: std::rt::lang_start::{{closure}}
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libstd/rt.rs:67
34: std::rt::lang_start_internal::{{closure}}
at src/libstd/rt.rs:52
35: std::panicking::try::do_call
at src/libstd/panicking.rs:331
36: std::panicking::try
at src/libstd/panicking.rs:274
37: std::panic::catch_unwind
at src/libstd/panic.rs:394
38: std::rt::lang_start_internal
at src/libstd/rt.rs:51
39: std::rt::lang_start
at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libstd/rt.rs:67
40: main
41: __libc_start_main
42: _start

[kianenigma]

So apparently for some particular set, the equalise resulted in a solution which has a slightly lower score than the original score.

This is related to paritytech/substrate#6693 and will be fixed asap. In the meantime, I'll change the subtract to be checked_sub and show a warning if in any case this happened.

Thanks for the report!