libra merge-base
Command reference for `libra merge-base`
Find the best common ancestor(s) of two commits — a focused subset of
git merge-base. Backed by the single lowest-common-ancestor (LCA)
implementation in internal/merge_base.rs, which diff A...B also uses.
Synopsis
libra merge-base <commit> <commit>
libra merge-base --all <commit> <commit>
libra merge-base --is-ancestor <commit> <commit>
Description
Given two commits, merge-base prints their best common ancestor — a true LCA:
a common ancestor that is not itself a strict ancestor of another common
ancestor. For a normal "Y" history that is the point where the branches
diverged. In criss-cross histories there can be several LCAs; --all prints all
of them, while the default prints one (deterministically chosen).
With --is-ancestor, nothing is printed; the exit code answers whether the
first commit is an ancestor of the second.
Each <commit> may be a branch, tag, HEAD, or an object id.
Options
| Option | Description | Example |
|---|---|---|
--all |
Print every lowest common ancestor, not just one. | libra merge-base --all main feature |
--is-ancestor |
Test ancestry (exit 0/1) instead of printing a base. | libra merge-base --is-ancestor v1 main |
--json / --machine |
Structured output: { bases: [...] } or { is_ancestor }. |
libra --json merge-base main feature |
Exit codes
| Code | Meaning |
|---|---|
0 |
A merge base was printed, or (--is-ancestor) the first commit is an ancestor of the second. |
1 |
No common ancestor exists, or (--is-ancestor) the first commit is not an ancestor of the second. No output. |
128 |
A commit could not be resolved, or the wrong number of arguments was given. |
Examples
# Where did main and feature diverge?
libra merge-base main feature
# Is the release tag still on the main line?
libra merge-base --is-ancestor v1.0 main && echo "yes, fast-forwardable"
# Diff a feature against where it branched from main
libra diff main...feature
Comparison with Git
| Task | Libra | Git |
|---|---|---|
| Best common ancestor | libra merge-base a b |
git merge-base a b |
| All merge bases | libra merge-base --all a b |
git merge-base --all a b |
| Ancestry test | libra merge-base --is-ancestor a b |
git merge-base --is-ancestor a b |
Deferred (not yet exposed): more than two commits and --octopus /
--independent / --fork-point. (The log / rebase internals still use their
own first-found walk; migrating them onto this shared LCA is a tracked
follow-up.)