Merge Bot ========= Setup ----- * Setup a project with relevant repositories and branches the bot should manage (e.g. odoo/odoo and 10.0). * Set up reviewers (github_login + boolean flag on partners). * Sync PRs. * Add "Issue comments","Pull requests" and "Statuses" webhooks to managed repositories. * If applicable, add "Statuses" webhook to the *source* repositories. Github does not seem to send statuses cross-repository when commits get transmigrated so if a user creates a branch in odoo-dev/odoo, waits for CI to run then creates a PR targeted to odoo/odoo the PR will never get status-checked (unless we modify runbot to re-send statuses on pull_request webhook). Working Principles ------------------ Useful information (new PRs, CI, comments, ...) is pushed to the MB via webhooks. Most of the staging work is performed via a cron job: 1. for each active staging, check if their are done 1. if successful * ``push --ff`` to target branches * close PRs 2. if only one batch, mark as failed for batches of multiple PRs, the MB attempts to infer which specific PR failed 3. otherwise split staging in 2 (bisection search of problematic batch) 2. for each branch with no active staging * if there are inactive stagings, stage one of them * otherwise look for batches targered to that PR (PRs grouped by label with branch as target) * attempt staging 1. reset temp branches (one per repo) to corresponding targets 2. merge each batch's PR into the relevant temp branch * on merge failure, mark PRs as failed 3. once no more batch or limit reached, reset staging branches to tmp 4. mark staging as active Commands -------- A command string is a line starting with the mergebot's name and followed by various commands. Self-reviewers count as reviewers for the purpose of their own PRs, but delegate reviewers don't. retry resets a PR in error mode to ready for staging can be used by a reviewer or the PR author to re-stage the PR after it's been updated or the target has been updated & fixed. r(review)+ approves a PR, can be used by a reviewer or delegate reviewer r(eview)- removes approval from a PR, currently only active for PRs in error mode: unclear what should happen if a PR got unapproved while in staging (cancel staging?), can be used by a reviewer or the PR author squash+/squash- marks the PR as squash or merge, can override squash inference or a previous squash command, can only be used by reviewers delegate+/delegate= adds either PR author or the specified (github) users as authorised reviewers for this PR. ```` is a comma-separated list of github usernames (no @), can be used by reviewers p(riority)=2|1|0 sets the priority to normal (2), pressing (1) or urgent (0), lower-priority PRs are selected first and batched together, can be used by reviewers currently only used for staging, but p=0 could cancel an active staging to force staging the specific PR and ignore CI on the PR itself? AKA pr=0 would cancel a pending staging and ignore (non-error) state? Q: what of co-dependent PRs, staging currently looks for co-dependent PRs where all are ready, could be something along the lines of:: (any(priority = 0) and every(state != error)) or every(state = ready) TODO ---- * PR edition (retarget, title/message) * Ability to disable/ignore branches in runbot (tmp branches where staging is being built) * What happens when cancelling staging during bisection TODO? ----- * Prioritize urgent PRs over existing batches? * Make autosquash dynamic? Currently PR marked as squash if only 1 commit on creation, this is not changed if more commits are added. * Use actual GH reviews? Currently only PR comments count. * Rebase? Not sure what use that would have & would need to be done by hand Structure --------- A *project* is used to manage multiple *repositories* across many *branches*. Each *PR* targets a specific branch in a specific repository. A *batch* is a number of co-dependent PRs, PRs which are assumed to depend on one another (the exact relationship is irrelevant) and thus always need to be batched together. Batches are normally created on the fly during staging. A *staging* is a number of batches (up to 8 by default) which will be tested together, and split if CI fails. Each staging applies to a single *branch* the target) across all managed repositories. Stagings can be active (currently live on the various staging branches) or inactive (to be staged later, generally as a result of splitting a failed staging). Notes ----- * When looking for stageable batches, priority is taken in account and isolating e.g. if there's a single high-priority PR, low-priority PRs are ignored completely and only that will be staged on its own * Reviewers are set up on partners so we can e.g. have author-tracking & deletate reviewers without needing to create proper users for every contributor. * MB collates statuses on commits independently from other objects, so a commit getting CI'd in odoo-dev/odoo then made into a PR on odoo/odoo should be correctly interpreted assuming odoo-dev/odoo sent its statuses to the MB. * Github does not support transactional sequences of API calls, so it's possible that "intermediate" staging states are visible & have to be rollbacked e.g. a staging succeeds in a 2-repo scenario, A.{target} is ff-d to A.{staging}, then B.{target}'s ff to B.{staging} fails, we have to rollback A.{target}. * Batches & stagings are non-permanent, they are deleted after success or failure. * Co-dependence is currently inferred through *labels*, which is a pair of ``{login}:{branchname}`` e.g. odoo-dev:11.0-pr-flanker-jke. If this label is present in a PR to A and a PR to B, these two PRs will be collected into a single batch to ensure they always get batched (and failed) together. Previous Work ------------- bors-ng ~~~~~~~ * r+: accept (only for trusted reviewers) * r-: unaccept * r=users...: accept on behalf of users * delegate+: allows author to self-review * delegate=users...: allow non-reviewers users to review * try: stage build (to separate branch) but don't merge on succes Why not bors-ng ############### * no concurrent staging (can only stage one target at a time) * can't do co-dependent repositories/multi-repo staging * cancels/forgets r+'d branches on FF failure (emergency pushes) instead of re-staging * unclear whether prioritisation supported homu ~~~~ Additionally to bors-ng's: * SHA option on r+/r=, guards * p=NUMBER: set priority (unclear if best = low/high) * rollup/rollup-: should be default * retry: re-attempt PR (flaky?) * delegate-: remove delegate+/delegate= * force: ??? * clean: ???