FA-75657 / Text diff and three-way merge / Member archive

Three-way key-value merge: deleting a key and setting it to null are the same state · case 02

Setting a value to null is merged as a deletion, and a deleted key can come back as null.

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Case contract

Merge base, ours and theirs maps key by key over the union of keys; an absent key and a key holding null are different states. If ours and theirs agree, take that state; else if ours equals base take theirs; else if theirs equals base take ours; otherwise record a conflict and keep ours. Return sorted merged [key, value] pairs and sorted conflicting keys.

Why this case matters

Structured configuration and lock files are merged per key, where deletions and null values must stay distinguishable.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
both delete the same key	`{"conflicts": [], "merged": [["host", "a"], ["mode", null], ["port", "80"]]}`	`{"conflicts": [], "merged": [["host", "a"], ["port", "80"]]}`	Failed

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