This discussion is for deciding what breaking changes we plan to make in Shadow 3.0. This list will be updated as we decide on what changes we'll make:

• [🟢] Remove the hosts.<hostname>.quantity configuration option — Remove configuration hosts.<hostname>.quantity field #2067. Done: Remove the host quantity config option #2868
• [🟢] Remove the hosts.<hostname>.processes[*].quantity configuration option — Done: Remove the process quantity config option #2873
• [🟢] Remove the host_defaults.pcap_directory configuration option, and add a new host_defaults.pcap_enabled boolean option — Done: Change the pcap_directory config option to pcap_enabled #2840
• [🟢] Rename the hosts.<hostname>.options configuration option — Rename host_defaults configuration field #2065. Done: Rename the host_defaults and options config fields #2883
• [🟢] Don't search current directory for process — Allow for sourcing executables from $PATH #2447 (comment). Done: Do not implicitly search current directory for executables #2824
• [🟢] Error if any process stop_time or start_time are >= than the simulation stop_time. Done: Fail if process start or stop time isn't before sim stop time #2859
• [🟢] Enable extended YAML syntax by default (remove experimental.use_extended_yaml field). Done: Always use YAML extended syntax #2831
• [🟢] Remove hostname prefix from data files — Remove hostname prefix from data files #2218. Done: Remove hostname prefix from hosts' data files #2833
• [🟢] Drop support for EOL distros — Drop support for EOL distros #2178
• [🟢] Change our support policy for EOL distros — Document how we decide which distros are supported #2309
• [🟢] Bump minimum cmake version to 3.12 — Bump minimum cmake version to 3.12 #2418 (edit: depends on if Ubuntu 18.04 is EOL by Shadow 3.0 release time)
• [🟢] Remove "_manager_heartbeat" string from heartbeat log message —

  shadow/src/main/core/manager.rs

  Line 805 in 8581e74

  _manager_heartbeat", // this is required for tornettools

  . Done: Remove the '_manager_heartbeat' string #2874
• [🟢] Change default behaviour of Shadow's exit status handling — Roadmapping: Graceful shutdown of managed processes #2034
• [🔺] Store the path to the shim somewhere other than the runpath (for example in a custom ELF section?) — Move Shadow's main function from C to Rust #2095
• [🟢] Disallow non-[a-z0-9-.] characters in the hostname — Done: Restrict allowed hostname characters #2856
• [🔺] Build tests by default — Build tests by default #2377
• [🟢] Drop official support for clang since we don't test it on all platforms in the CI
• [🟢] Drop support for CentOS (we don't know anyone who uses CentOS, and hopefully Fedora covers a lot of the same testing cases) to reduce CI usage
• [🟢] Remove documented pid assignment order. Assign PIDs in process creation order #2908
• [🟢] Remove process 'exitcode' file Drop per-process exitcode files #2906
• [🟢] Change the process environment option from a string to a map — Done: Change the process 'environment' option to a map #2875
• [🟢] Rename the pcap files to use the interface name rather than the IP address — Done: Change pcap filenames to use the interface name #2876
• [🟢] Remove --profile option from setup script — Remove --profile option from setup script #2405. Done: Clean up setup script options #2892
• [🟢] Enable spinning in scheduler by default for the 3.0 pre-release, but re-evaluate before the final 3.0 release — Spinning in the scheduler #2877. Done: Enable the experimental worker spinning by default #2909

Legend:
🟢: Done (yay)
🟨: Planned
🔺: Not planned
❔: Undecided