title: How safe are automatic merges in Mercurial?
body: <p>In Mercurial there is the <a href="http://mercurial.selenic.com/wiki/FetchExtension" rel="noreferrer">fetch extension</a> that you can use to emulate something like <code>svn update</code>, i.e. to merge with incoming changes without even looking at them. But even if you don't use <code>hg fetch</code>, most of your merges will "miraculously" work without resulting in a conflict. This is great, but how safe is it to trust such merges to be valid merges of, say, Java code?</p>
  
  <p>Are there any examples to demonstrate why or when these merges should be (or shouldn't be) trusted?</p>