In my previous blog post Providing online reference documentation for debputy, I made a point about how debhelper documentation was suboptimal on account of being static rather than online. The thing is that debhelper is not alone in this problem space, even if it is a major contributor to the number of packaging files you have to to know about.
If we look at the "competition" here such as Fedora and Arch Linux, they tend to only have one packaging file. While most Debian people will tell you a long list of cons about having one packaging file (such a Fedora's spec file being 3+ domain specific languages "mashed" into one file), one major advantage is that there is only "the one packaging file". You only need to remember where to find the documentation for one file, which is great when you are running on wetware with limited storage capacity.
Which means as a newbie, you can dedicate less mental resources to tracking multiple files and how they interact and more effort understanding the "one file" at hand. I started by asking myself how can we in Debian make the packaging stack more accessible to newcomers? Spoiler alert, I dug myself into rabbit hole and ended up somewhere else than where I thought I was going.
I started by wanting to scan the debian directory and annotate all files that I could with documentation links. The logic was that if debputy could do that for you, then you could spend more mental effort elsewhere. So I combined debputy's packager provided files detection with a static list of files and I quickly had a good starting point for debputy-based packages.
Adding (non-static) dpkg and debhelper files to the mix
Now, I could have closed the topic here and said "Look, I did debputy files plus couple of super common files". But I decided to take it a bit further. I added support for handling some dpkg files like packager provided files (such as debian/substvars and debian/symbols). But even then, we all know that debhelper is the big hurdle and a major part of the omission...
In another previous blog post (A new Debian package helper: debputy), I made a point about how debputy could list all auxiliary files while debhelper could not. This was exactly the kind of feature that I would need for this feature, if this feature was to cover debhelper. Now, I also remarked in that blog post that I was not willing to maintain such a list. Also, I may have ranted about static documentation being unhelpful for debhelper as it excludes third-party provided tooling.
Fortunately, a recent update to dh_assistant had provided some basic plumbing for loading dh sequences. This meant that getting a list of all relevant commands for a source package was a lot easier than it used to be. Once you have a list of commands, it would be possible to check all of them for dh's NOOP PROMISE hints. In these hints, a command can assert it does nothing if a given pkgfile is not present. This lead to the new dh_assistant list-guessed-dh-config-files command that will list all declared pkgfiles and which helpers listed them.
With this combined feature set in place, debputy could call dh_assistant to get a list of pkgfiles, pretend they were packager provided files and annotate those along with manpage for the relevant debhelper command. The exciting thing about letting debpputy resolve the pkgfiles is that debputy will resolve "named" files automatically (debhelper tools will only do so when --name is passed), so it is much more likely to detect named pkgfiles correctly too. Side note: I am going to ignore the elephant in the room for now, which is dh_installsystemd and its package@.service files and the wide-spread use of debian/foo.service where there is no package called foo. For the latter case, the "proper" name would be debian/pkg.foo.service.
With the new dh_assistant feature done and added to debputy, debputy could now detect the ubiquitous debian/install file. Excellent. But less great was that the very common debian/docs file was not. Turns out that dh_installdocs cannot be skipped by dh, so it cannot have NOOP PROMISE hints. Meh...
Well, dh_assistant could learn about a new INTROSPECTABLE marker in addition to the NOOP PROMISE and then I could sprinkle that into a few commands. Indeed that worked and meant that debian/postinst (etc.) are now also detectable.
At this point, debputy would be able to identify a wide range of debhelper related configuration files in debian/ and at least associate each of them with one or more commands.
Nice, surely, this would be a good place to stop, right...?
Adding more metadata to the files
The debhelper detected files only had a command name and manpage URI to that command. It would be nice if we could contextualize this a bit more.
Like is this file installed into the package as is like debian/pam or is it a file list to be processed like debian/install. To make this distinction, I could add the most common debhelper file types to my static list and then merge the result together.
Except, I do not want to maintain a full list in debputy. Fortunately, debputy has a quite extensible plugin infrastructure, so added a new plugin feature to provide this kind of detail and now I can outsource the problem! I split my definitions into two and placed the generic ones in the debputy-documentation plugin and moved the debhelper related ones to debhelper-documentation. Additionally, third-party dh addons could provide their own debputy plugin to add context to their configuration files.
So, this gave birth file categories and configuration features, which described each file on different fronts. As an example, debian/gbp.conf could be tagged as a maint-config to signal that it is not directly related to the package build but more of a tool or style preference file. On the other hand, debian/install and debian/debputy.manifest would both be tagged as a pkg-helper-config. Files like debian/pam were tagged as ppf-file for packager provided file and so on.
I mentioned configuration features above and those were added because, I have had a beef with debhelper's "standard" configuration file format as read by filearray and filedoublearray. They are often considered simple to understand, but it is hard to know how a tool will actually read the file. As an example, consider the following:
- Will the debhelper use filearray, filedoublearray or none of them to read the file? This topic has about 2 bits of entropy.
- Will the config file be executed if it is marked executable assuming you are using the right compat level? If it is executable, does dh-exec allow renaming for this file? This topic adds 1 or 2 bit of entropy depending on the context.
- Will the config file be subject to glob expansions? This topic sounds like a boolean but is a complicated mess. The globs can be handled either by debhelper as it parses the file for you. In this case, the globs are applied to every token. However, this is not what dh_install does. Here the last token on each line is supposed to be a directory and therefore not subject to globs. Therefore, dh_install does the globbing itself afterwards but only on part of the tokens. So that is about 2 bits of entropy more. Actually, it gets worse...
- If the file is executed, debhelper will refuse to expand globs in the output of the command, which was a deliberate design choice by the original debhelper maintainer took when he introduced the feature in debhelper/8.9.12. Except, dh_install feature interacts with the design choice and does enable glob expansion in the tool output, because it does so manually after its filedoublearray call.
So these "simple" files have way too many combinations of how they can be interpreted. I figured it would be helpful if debputy could highlight these difference, so I added support for those as well.
Accordingly, debian/install is tagged with multiple tags including dh-executable-config and dh-glob-after-execute. Then, I added a datatable of these tags, so it would be easy for people to look up what they meant.
Ok, this seems like a closed deal, right...?
Context, context, context
However, the dh-executable-config tag among other are only applicable in compat 9 or later. It does not seem newbie friendly if you are told that this feature exist, but then have to read in the extended description that that it actually does not apply to your package.
This problem seems fixable. Thanks to dh_assistant, it is easy to figure out which compat level the package is using. Then tweak some metadata to enable per compat level rules. With that tags like dh-executable-config only appears for packages using compat 9 or later.
Also, debputy should be able to tell you where packager provided files like debian/pam are installed. We already have the logic for packager provided files that debputy supports and I am already using debputy engine for detecting the files. If only the plugin provided metadata gave me the install pattern, debputy would be able tell you where this file goes in the package. Indeed, a bit of tweaking later and setting install-pattern to usr/lib/pam.d/{name}, debputy presented me with the correct install-path with the package name placing the {name} placeholder.
Now, I have been using debian/pam as an example, because debian/pam is installed into usr/lib/pam.d in compat 14. But in earlier compat levels, it was installed into etc/pam.d. Well, I already had an infrastructure for doing compat file tags. Off we go to add install-pattern to the complat level infrastructure and now changing the compat level would change the path. Great. (Bug warning: The value is off-by-one in the current version of debhelper. This is fixed in git)
Also, while we are in this install-pattern business, a number of debhelper config files causes files to be installed into a fixed directory. Like debian/docs which causes file to be installed into /usr/share/docs/{package}. Surely, we can expand that as well and provide that bit of context too... and done. (Bug warning: The code currently does not account for the main documentation package context)
It is rather common pattern for people to do debian/foo.in files, because they want to custom generation of debian/foo. Which means if you have debian/foo you get "Oh, let me tell you about debian/foo ". Then you rename it to debian/foo.in and the result is "debian/foo.in is a total mystery to me!". That is suboptimal, so lets detect those as well as if they were the original file but add a tag saying that they are a generate template and which file we suspect it generates.
Finally, if you use debputy, almost all of the standard debhelper commands are removed from the sequence, since debputy replaces them. It would be weird if these commands still contributed configuration files when they are not actually going to be invoked. This mostly happened naturally due to the way the underlying dh_assistant command works. However, any file mentioned by the debhelper-documentation plugin would still appear unfortunately. So off I went to filter the list of known configuration files against which dh_ commands that dh_assistant thought would be used for this package.
Wrapping it up
I was several layers into this and had to dig myself out. I have ended up with a lot of data and metadata. But it was quite difficult for me to arrange the output in a user friendly manner.
However, all this data did seem like it would be useful any tool that wants to understand more about the package. So to get out of the rabbit hole, I for now wrapped all of this into JSON and now we have a debputy tool-support annotate-debian-directory command that might be useful for other tools.
To try it out, you can try the following demo:
In another day, I will figure out how to structure this output so it is useful for non-machine consumers. Suggestions are welcome. :)
Limitations of the approach
As a closing remark, I should probably remind people that this feature relies heavily on declarative features. These include:
- When determining which commands are relevant, using Build-Depends: dh-sequence-foo is much more reliable than configuring it via the Turing complete configuration we call debian/rules.
- When debhelper commands use NOOP promise hints, dh_assistant can "see" the config files listed those hints, meaning the file will at least be detected. For new introspectable hint and the debputy plugin, it is probably better to wait until the dust settles a bit before adding any of those.
You can help yourself and others to better results by using the declarative way rather than using debian/rules, which is the bane of all introspection!