Function pointer comparisons are non-deterministic

[sebastianrasor]

In trying to package River in Nix, I've come across the following issue where tests are failing:

       > failures:
       >
       > ---- config::toml::test::load_test stdout ----
       > thread 'config::toml::test::load_test' panicked at source/river/src/config/toml.rs:403:9:
       > assertion `left == right` failed
       >   left: "Config { validate_configs: false, threads_per_service: 8, daemonize: false, pid_file: None, upgrade_socket: None, upgrade: false, basic_proxies: [ProxyConfig { name: \"Example1\", listeners: [ListenerConfig { source: Tcp { addr: \"0.0.0.0:8080\", tls: None, offer_h2: false } }, ListenerConfig { source: Tcp { addr: \"0.0.0.0:4443\", tls: Some(TlsConfig { cert_path: \"./assets/test.crt\", key_path: \"./assets/test.key\" }), offer_h2: false } }], upstream_options: UpstreamOptions { selection: RoundRobin, selector: 0x555555674510, health_checks: None, discovery: Static }, upstreams: [HttpPeer { _address: Inet(91.107.223.4:443), scheme: HTTPS, sni: \"onevariable.com\", proxy: None, client_cert_key: None, group_key: 0, options: PeerOptions { bind_to: None, connection_timeout: None, total_connection_timeout: None, read_timeout: None, idle_timeout: None, write_timeout: None, verify_cert: true, verify_hostname: true, alternative_cn: None, alpn: H1, ca: None, tcp_keepalive: None, tcp_recv_buf: None, dscp: None, no_header_eos: false, h2_ping_interval: None, max_h2_streams: 1, extra_proxy_headers: {}, curves: None, second_keyshare: true, tcp_fast_open: false, tracer: None } }], path_control: PathControl { request_filters: [], upstream_request_filters: [{\"kind\": \"remove-header-key-regex\", \"pattern\": \".*(secret|SECRET).*\"}, {\"key\": \"x-proxy-friend\", \"kind\": \"upsert-header\", \"value\": \"river\"}], upstream_response_filters: [{\"kind\": \"remove-header-key-regex\", \"pattern\": \".*ETag.*\"}, {\"key\": \"x-with-love-from\", \"kind\": \"upsert-header\", \"value\": \"river\"}] }, rate_limiting: RateLimitingConfig { rules: [] } }, ProxyConfig { name: \"Example2\", listeners: [ListenerConfig { source: Tcp { addr: \"0.0.0.0:8000\", tls: None, offer_h2: false } }], upstream_options: UpstreamOptions { selection: RoundRobin, selector: 0x555555674510, health_checks: None, discovery: Static }, upstreams: [HttpPeer { _address: Inet(91.107.223.4:80), scheme: HTTP, sni: \"\", proxy: None, client_cert_key: None, group_key: 0, options: PeerOptions { bind_to: None, connection_timeout: None, total_connection_timeout: None, read_timeout: None, idle_timeout: None, write_timeout: None, verify_cert: true, verify_hostname: true, alternative_cn: None, alpn: H1, ca: None, tcp_keepalive: None, tcp_recv_buf: None, dscp: None, no_header_eos: false, h2_ping_interval: None, max_h2_streams: 1, extra_proxy_headers: {}, curves: None, second_keyshare: true, tcp_fast_open: false, tracer: None } }], path_control: PathControl { request_filters: [], upstream_request_filters: [], upstream_response_filters: [] }, rate_limiting: RateLimitingConfig { rules: [] } }], file_servers: [] }"
       >  right: "Config { validate_configs: false, threads_per_service: 8, daemonize: false, pid_file: None, upgrade_socket: None, upgrade: false, basic_proxies: [ProxyConfig { name: \"Example1\", listeners: [ListenerConfig { source: Tcp { addr: \"0.0.0.0:8080\", tls: None, offer_h2: false } }, ListenerConfig { source: Tcp { addr: \"0.0.0.0:4443\", tls: Some(TlsConfig { cert_path: \"./assets/test.crt\", key_path: \"./assets/test.key\" }), offer_h2: false } }], upstream_options: UpstreamOptions { selection: RoundRobin, selector: 0x55555566f4c0, health_checks: None, discovery: Static }, upstreams: [HttpPeer { _address: Inet(91.107.223.4:443), scheme: HTTPS, sni: \"onevariable.com\", proxy: None, client_cert_key: None, group_key: 0, options: PeerOptions { bind_to: None, connection_timeout: None, total_connection_timeout: None, read_timeout: None, idle_timeout: None, write_timeout: None, verify_cert: true, verify_hostname: true, alternative_cn: None, alpn: H1, ca: None, tcp_keepalive: None, tcp_recv_buf: None, dscp: None, no_header_eos: false, h2_ping_interval: None, max_h2_streams: 1, extra_proxy_headers: {}, curves: None, second_keyshare: true, tcp_fast_open: false, tracer: None } }], path_control: PathControl { request_filters: [], upstream_request_filters: [{\"kind\": \"remove-header-key-regex\", \"pattern\": \".*(secret|SECRET).*\"}, {\"key\": \"x-proxy-friend\", \"kind\": \"upsert-header\", \"value\": \"river\"}], upstream_response_filters: [{\"kind\": \"remove-header-key-regex\", \"pattern\": \".*ETag.*\"}, {\"key\": \"x-with-love-from\", \"kind\": \"upsert-header\", \"value\": \"river\"}] }, rate_limiting: RateLimitingConfig { rules: [] } }, ProxyConfig { name: \"Example2\", listeners: [ListenerConfig { source: Tcp { addr: \"0.0.0.0:8000\", tls: None, offer_h2: false } }], upstream_options: UpstreamOptions { selection: RoundRobin, selector: 0x55555566f4c0, health_checks: None, discovery: Static }, upstreams: [HttpPeer { _address: Inet(91.107.223.4:80), scheme: HTTP, sni: \"\", proxy: None, client_cert_key: None, group_key: 0, options: PeerOptions { bind_to: None, connection_timeout: None, total_connection_timeout: None, read_timeout: None, idle_timeout: None, write_timeout: None, verify_cert: true, verify_hostname: true, alternative_cn: None, alpn: H1, ca: None, tcp_keepalive: None, tcp_recv_buf: None, dscp: None, no_header_eos: false, h2_ping_interval: None, max_h2_streams: 1, extra_proxy_headers: {}, curves: None, second_keyshare: true, tcp_fast_open: false, tracer: None } }], path_control: PathControl { request_filters: [], upstream_request_filters: [], upstream_response_filters: [] }, rate_limiting: RateLimitingConfig { rules: [] } }], file_servers: [] }"
       > note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
       >
       > ---- config::kdl::test::load_test stdout ----
       > thread 'config::kdl::test::load_test' panicked at source/river/src/config/kdl/test.rs:194:9:
       > assertion `left == right` failed
       >   left: UpstreamOptions { selection: RoundRobin, selector: 0x55555567f1e0, health_checks: None, discovery: Static }
       >  right: UpstreamOptions { selection: RoundRobin, selector: 0x5555556602a0, health_checks: None, discovery: Static }
       >
       >
       > failures:
       >     config::kdl::test::load_test
       >     config::toml::test::load_test
       >
       > test result: FAILED. 5 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.60s

I believe the issue here is related to selector being a function pointer. The debug representation of a function pointer is its address, but I believe that function pointer comparisons are non-deterministic: rust-lang/rust#54685 (comment)