GooseMetrics::print panics when using --no-task-metrics since version 0.13.1

[cppforliving]

Minimal example to reproduce the issue

Cargo.toml

[package]
name = "goose-panic"
version = "0.1.0"
edition = "2018"

[dependencies]
goose = "=0.13.1"

src/main.rs

use goose::prelude::*;

fn main() -> Result<(), GooseError> {
    GooseAttack::initialize()?
        .register_taskset(taskset!("no-op"))
        .execute()?
        .print();
    Ok(())
}

Without --no-task-metrics there is no panic

$ RUST_BACKTRACE=1 cargo run -- --host http://localhost -t 1
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/goose-panic --host 'http://localhost' -t 1`

 === PER TASK METRICS ===
 ------------------------------------------------------------------------------
 Name                     |   # times run |        # fails |   task/s |  fail/s
 ------------------------------------------------------------------------------
 ------------------------------------------------------------------------------
 Name                     |    Avg (ms) |        Min |         Max |     Median
 ------------------------------------------------------------------------------
 ------------------------------------------------------------------------------
 Slowest page load within specified percentile of requests (in ms):
 ------------------------------------------------------------------------------
 Name                     |    50% |    75% |    98% |    99% |  99.9% | 99.99%
 ------------------------------------------------------------------------------
 ------------------------------------------------------------------------------
 Users: 1
 Target host: http://localhost/
 During: 2021-08-25 13:45:01 - 2021-08-25 13:45:02 (duration: 00:00:01)

 goose v0.13.1
 ------------------------------------------------------------------------------

However adding --no-task-metrics causes GooseMetrics::print panic

$ RUST_BACKTRACE=1 cargo run -- --host http://localhost -t 1 --no-task-metrics
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/goose-panic --host 'http://localhost' -t 1 --no-task-metrics`
 ------------------------------------------------------------------------------
 Slowest page load within specified percentile of requests (in ms):
 ------------------------------------------------------------------------------
 Name                     |    50% |    75% |    98% |    99% |  99.9% | 99.99%
 ------------------------------------------------------------------------------
 ------------------------------------------------------------------------------
 Users: 1
thread 'main' panicked at 'internal error: entered unreachable code', /home/builder/.cargo/registry/src/github.com-1ecc6299db9ec823/goose-0.13.1/src/metrics.rs:2051:17
stack backtrace:
   0: rust_begin_unwind
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:50:5
   3: goose::metrics::GooseMetrics::fmt_overview
             at /home/builder/.cargo/registry/src/github.com-1ecc6299db9ec823/goose-0.13.1/src/metrics.rs:2051:17
   4: <goose::metrics::GooseMetrics as core::fmt::Display>::fmt
             at /home/builder/.cargo/registry/src/github.com-1ecc6299db9ec823/goose-0.13.1/src/metrics.rs:2128:9
   5: <&T as core::fmt::Display>::fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/fmt/mod.rs:2031:62
   6: core::fmt::write
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/fmt/mod.rs:1110:17
   7: std::io::Write::write_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/io/mod.rs:1588:15
   8: <&std::io::stdio::Stdout as std::io::Write>::write_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/io/stdio.rs:657:9
   9: <std::io::stdio::Stdout as std::io::Write>::write_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/io/stdio.rs:631:9
  10: std::io::stdio::print_to
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/io/stdio.rs:934:21
  11: std::io::stdio::_print
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/io/stdio.rs:947:5
  12: goose::metrics::GooseMetrics::print
             at /home/builder/.cargo/registry/src/github.com-1ecc6299db9ec823/goose-0.13.1/src/metrics.rs:944:13
  13: goose_panic::main
             at ./src/main.rs:4:5
  14: core::ops::function::FnOnce::call_once
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

When using older version 0.13.0, the panic does not happen.

[jeremyandrews]

Thanks for the bug report! I can duplicate, and will be sure this is fixed in the next release.

[cppforliving]

Thank you for such a quick fix :)