Wednesday, July 28, 2010

PostgreSQL and Flymake

Flymake is an on-the-fly syntax checker for Emacs. Here is how you can use it for editing the PostgreSQL source code. Add this to your src/Makefile.custom:
        $(COMPILE.c) -fsyntax-only $(CHK_SOURCES)
Then you can activate the flymake minor mode either manually using M-x flymake-mode, or by adding it to your Emacs customization for PostgreSQL. I use:
(defun pgsql-c-mode ()
  "C mode adjusted for PostgreSQL project"

  ; .. and the rest ...
Here is a screenshot:
Notice the marked line with the syntax error and the tooltip/popup with the error message, which appears when the mouse hovers over the marked line.

Note, however, that since activating flymake will essentially cause a compiler to be running continuously in the background, this is not what you want to use when hacking PostgreSQL on the road. ;-)

Saturday, July 3, 2010

Increasing the priority of Debian experimental

Many people run Debian testing or unstable or some mix thereof.  This works pretty well for a development system or a general desktop system if you know a bit about what you're doing (note: nonetheless officially not recommended).  Sometimes you throw packages from experimental into the mix, if you want to get the latest stuff that isn't yet fully integrated into the rest of Debian.

The default APT priority of the Debian experimental release is 1, which ensures that it is never automatically installed or upgraded. This is not always ideal, in my experience. Of course, you don't want a package from experimental to take precedence over a package from stable, testing, or unstable by default. But I think when you have in the past installed a package from experimental, you probably want to pull in upgrades to that package from experimental as well. Otherwise, you will end up with completely unmaintained packages on your system.  That is because in practice many packages in experimental are not actually experimental or broken or unmaintained, but just an advance branch of some software that is just for some reason not ready to go down the unstable-testing-stable road.

To make this work better, I have set the priority of experimental to 101 in my /etc/apt/preferences:
Package: *
Pin: release experimental
Pin-Priority: 101
Now the following will happen: If you just apt-get install a package, it will come from whatever "normal" release you have in your sources.list, say stable or testing. You can override that using -t experimental as usual. If you install a package from experimental and later an upgrade is available in experimental, apt-get upgrade will install that automatically. Also, if an upgrade in a "normal" release appears that has a higher version number, that version will be installed.

Of course, caveats apply. Some software in experimental is really experimental and should only be installed under close supervision. If a package is available only in experimental, this setup will install it when you ask for the package, even if you might not have actually wanted it if you had known that it was in experimental. Figure it out yourself. :)

Similar considerations apply to backports. I use
Package: *
Pin: release a=lenny-backports
Pin-Priority: 102
On the system I have in mind here, the standard distribution is stable, testing is 101, and backports is 102, taking precedence over testing. Because for some architecture-independent packages you don't need backports, so you can pull them directly from testing that way.

In general, the APT priority business is relatively powerful and often a good alternative to, say, manually downloading packages from various distributions, installing them manually, forgetting where they came from, and never upgrading them.