freebsd-update: Fail if there are any unresolved conflicts

[emaste]

Summary

Unresolved conflicts can break system files so it is important to make sure that
the user fixes all of them.

PR: 185546

Test Plan

None

[aryeeteygerald_rogers.com]

An error or forcing them to resolve it manually again may be better.

[aryeeteygerald_rogers.com]

• Change unresolved conflict warning into an error

[rgrimes]

This makes "+<+ current version" a magic line that must never appear in any configuration file, are we ok with that?

[emaste]

In D18942#404799, @rgrimes wrote:

This makes "+<+ current version" a magic line that must never appear in any configuration file, are we ok with that?

Note that it is anchored to ^ and $ so must be exactly that line -- I think this restriction is OK.

[aryeeteygerald_rogers.com]

Also I perform a diff against the old version first so they must have added a line that looks like the diff marker during conflict resolution. This seems very unlikely.

[rgrimes]

In D18942#405541, @aryeeteygerald_rogers.com wrote:

Also I perform a diff against the old version first so they must have added a line that looks like the diff marker during conflict resolution. This seems very unlikely.

A common tactic to resolve but leave intact the issue if the specific file has a form of #if 0 #end construct is to do exactly that and leave it for later resolution, I think that your use of magic would prevent that methodology. Always always always try to not make magic things, history has repeatedly shown us that they are bad.

[emaste]

D37703 instead