# PR#73: An Approval Survives a Rebase

> **WARNING:** This document describes only the change applied in this PR.
> It may already be outdated once the next PR is merged.
> Historic PR documentation is not maintained along with new PRs; treat it as a snapshot.

## The Problem

Gitea dismisses an approval when new commits arrive (`dismiss_stale_approvals`).
A rebase onto `main`, or a merge of `main` into the branch, thus costs a new human approval,
although the change of the PR stays the same.
werkator PR#137 needed three approvals of the same change in this way.

## Non-Goals

- No carry-over of an approval that a human dismissed by hand or revoked with "request changes".
- No check that the merged `main` still fits the change semantically; the CI (`werkator`) stays required for that.
- No calibration of the Jev thresholds for corrections; this PR uses those of `[path_judge]`.

## The Scenarios

### Feature: an approval survives a rebase

#### Scenario#73.01: a rebase keeps the approval

So that a rebase onto `main` costs no new human approval.

- **Given** a human approved the head A of a PR
- **When** the PR is rebased onto a newer `main` without a conflict
- **Then** werkrevisor approves the new head without Jev and without a model call
- **And** its reason names the approval of A

##### Verified by

- [test_carry_over.CarryOverTest.test_a_rebase_keeps_the_approval](../../tests/test_carry_over.py)

#### Scenario#73.02: a small correction after a merge keeps the approval

So that a resolved merge conflict needs no human when Jev rates it as harmless.

- **Given** a human approved the head A of a PR
- **And** the new head has a changed block that A did not have
- **And** Jev rates that block below the thresholds of `[path_judge]`
- **When** werkrevisor reviews the new head
- **Then** it approves without a model call

##### Verified by

- [test_carry_over.CarryOverTest.test_a_harmless_correction_keeps_the_approval](../../tests/test_carry_over.py)

#### Scenario#73.03: a risky correction gets a review of the correction only

So that approved changes do not block the PR again.

- **Given** a human approved the head A of a PR
- **And** Jev rates a new block as risky
- **When** werkrevisor reviews the new head
- **Then** the model gets only the files with new blocks
- **And** a finding on the lines of an approved block is a hint

##### Verified by

- [test_carry_over.CarryOverTest.test_a_risky_correction_gets_a_review](../../tests/test_carry_over.py)
- [test_carry_over.CarryOverTest.test_a_finding_on_approved_lines_is_a_hint](../../tests/test_carry_over.py)
- [test_carry_over.ChangeKindTest.test_the_kind_comes_from_the_files_outside_the_approval](../../tests/test_carry_over.py)

#### Scenario#73.04: an approval dismissed by hand is not carried over

So that a human can take back an approval.

- **Given** a human dismissed the approval by hand
- **When** werkrevisor reviews the new head
- **Then** the model reviews every changed file

##### Verified by

- [test_carry_over.CarryOverTest.test_an_approval_dismissed_by_hand_is_not_carried_over](../../tests/test_carry_over.py)

#### Scenario#73.05: a dropped approved change is not carried over

So that a check that the PR added cannot disappear unnoticed in a rebase.

- **Given** a human approved the head A of a PR
- **When** a rebase drops a changed block of A
- **Then** the next review gives the model every changed file
- **And** a hint names the number of missing blocks

##### Verified by

- [test_carry_over.CarryOverTest.test_a_dropped_block_ends_the_carry_over](../../tests/test_carry_over.py)

#### Scenario#73.06: blocks approved by werkrevisor do not block again

So that a rebase after a GREEN review brings no new blocking findings on unchanged lines.

- **Given** werkrevisor approved the head A of a PR as GREEN
- **When** werkrevisor reviews the rebased head
- **Then** a finding on a block of A is a hint

##### Verified by

- [test_carry_over.CarryOverTest.test_blocks_of_a_green_review_do_not_block_again](../../tests/test_carry_over.py)

## The Solution

- Every result comment gets a hidden marker with a fingerprint per changed block:
  the path, the removed and the added lines, without line numbers and without context.
- A review looks for the newest approval of a head other than the current one:
  a human approval that Gitea dismissed automatically, or a GREEN approval of werkrevisor itself.
  The fingerprints come from the result comment of werkrevisor for that head.
- After a human approval, files with approved blocks only are left out of Jev and the model, like mechanical files.
  Without new blocks, werkrevisor approves; with new blocks, Jev judges their files first.
- A finding of the model on approved lines only is a hint.
- The change kind, which the model checks, comes from the files outside the approval.
- `[gate] carry_over_approvals = false` switches the carry-over of human approvals off.
- The README explains it under "Approval after a rebase"; the decision diagram shows both shortcuts.
- Version 0.32.0.

## Open Questions

- [x] Can werkrevisor compare the approved head with the new one through the Gitea API?
  Not directly: the compare route with `.diff` answers 404 for a private repository, even with a token.
  So each review keeps the fingerprints of its own head in its result comment.
- [x] How does werkrevisor tell an approval dismissed by a push from one dismissed by hand?
  Gitea's timeline has a `dismiss_review` event; after a push its text is
  "New commits pushed, approval review dismissed automatically", by hand it is the text of the human.

## Additional Changes

- The Werkbaum gets the plan `#werkregie.pwa`: the Werkregie frontend becomes a PWA; this PR does not implement it.

## Follow-up PRs

- Calibrate the Jev thresholds for corrections on real rebases, e.g. werkator PR#137, see `#gate.carry.calibrate`.