FA-75622 / Text diff and three-way merge / Member archive
Merge base selection: traversal follows only first parents · case 02
History reachable only through a merge's second parent is ignored and the base is too old or missing.
Case contract
Given a commit graph (commit -> parent list) and two commits, ancestors include the commit itself and all commits reachable through any parent. The merge bases are the common ancestors that are not ancestors of another common ancestor. Return them sorted.
Why this case matters
A three-way merge is only as good as its base; criss-cross histories legitimately have several best common ancestors.
One recorded failure
Sample boundary fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| merge commit sees both parents | ["B"] | ["D"] | Failed |
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