How to tell if a merge is needed after a pull in Mercurial?

Question

I have a clone of a repository with one head, nice and simple. After pulling in someone else's changes, I have a script that counts the heads to see if a merge is required. But if the other person has made a branch and merged it, "hg heads" shows two heads, and the script thinks it has to merge. What should the test really be?

Before:

0 - 1

After:

0 - 1 - 2 - 3
    \  /
     4 (branch)

This doesn't need merging. But a simple comparison of the number of heads before and after would suggest that it does. Why does Mercurial even show more than one head in this case?

Answer 1

Instead of calling hg heads call hg heads --topo which shows only topological heads -- those with no kids. You're see the head of their merged branch, but since it was merged in it's not a topological head and --topo will suppress it.

Answer 2

If you don't have spaces in your branch names, then you can use this script:

#!/bin/sh

for b in $(hg branches -q); do
    h=$(hg heads --template "." $b)
    if test ${#h} -gt 1; then
        echo "Branch $b needs merging, it has ${#h} heads"
    fi
done

It iterates over each open branch and counts the number of heads on it.