Why does APT want to upgrade my package?

Question

I need nginx compiled with a special flag, so I grabbed the source from the nginx stable PPA (apt-get source), changed debian/rules, built it and packaged it with debuild/dpkg-buildpackage, and installed the necessary .debs -- so far so good.

Only now APT wants to switch my local package with the one from the repository. This is a little puzzling since both packages have the exact same version:

$ dpkg -l nginx-full
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                    Version                                 Description
+++-=======================================-=======================================-==============================================================================================
ii  nginx-full                              1.2.1-0ubuntu0ppa1~precise              nginx web/proxy server (standard version)

and

$ sudo apt-get upgrade -s
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be upgraded:
  nginx-full
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Inst nginx-full [1.2.1-0ubuntu0ppa1~precise] (1.2.1-0ubuntu0ppa1~precise Stable:12.04/precise [amd64])
Conf nginx-full (1.2.1-0ubuntu0ppa1~precise Stable:12.04/precise [amd64])

Why exactly is this happening, and what's the best way of stopping it? Ideally, APT should offer to upgrade my package only with a strictly newer version, which would be a cue for me to rebuild my patched version with the newest source.

I've come across this bug report which looks pretty relevant, but since it contained no satisfactory work-around, I'm leaving the question open.

Answer 1

You manage what gets updated by what using the version number, which is set from whatever is the top line in debian/changelog in the source package when the package is built into a deb. If you want a different version from what is in the PPA you need to set your own version number greater than what is in the PPA.

As a word of caution, note that 1.2.3-1ppa1~2 is less than 1.2.3-1ppa1, so apt-get upgrade would upgrade to 1.2.3-1ppa1. (There's magic in the "~", it is less than anything, including the end of the version number. I see you and the PPA have this symbol in your package version number.