Contributing to the MySQL++ Project

If you wish to make any changes to the project’s files, here are some rules and hints to keep in mind while you work.

Getting Started with Fossil

The MySQL++ software project is hosted using the Fossil distributed version control system, which provides most of the features of GitHub without the complexities of Git.

I recommend one of three paths to learning Fossil:

I do not recommend starting with the Fossil doc index and seeking topics out from there; not to begin with, anyway. That path is best once you have some Fossil experience and know what you’re looking for.

If you have questions about Fossil, ask on the Fossil forum where I, your humble project maintainer, am active. I also work on the Fossil docs quite a bit, so if your question really isn’t answered somewhere in the above material, I might just solve it by extending the Fossil docs.

Fossil is available in many binary package repositories, and there are official precompiled binaries for several popular platforms. The project repository requires at least Fossil version 2.1, so if you’re stuck with a Fossil 1.x binary, you will have to build Fossil from source.

Fossil Anonymous Access

There are three ways to clone the repository anonymously using Fossil. Each of these methods gets you a file called mysqlpp.fossil containing the abridged version history back to the project’s founding.

You only need to take one of these options, once per machine. Thereafter, you will just be working with the cloned repository.

One-Step Clone-and-Open

The easiest way requires Fossil 2.14 or higher:

$ fossil clone
$ cd mysqlpp

That gets you a clone of the mysqlpp.fossil repository plus a check-out of the current trunk in a mysqlpp/ directory alongside it. We recommend that you do this in a directory like ~/src so you don’t commingle these files with other things in your current working directory.

Open from URI

If you have Fossil 2.12 or 2.13, the next-easiest method is:

$ mkdir -p ~/src/mysqlpp
$ cd ~/src/mysqlpp
$ fossil open

This opens the repository referenced by that URI into the current directory as mysqlpp.fossil, then opens that repo into that same subdirectory.

You have to create the destination directory first with this method because Fossil will refuse to spam a non-empty directory with the check-out contents when opening the repo into a directory containing other files unless you give it the --force flag.

Notice that the repo file ends up inside the check-out tree with this method. This is because of a purposeful semantic difference in Fossil between “open” and “clone.” It may seem strange to someone coming from Git, but while we don’t want to get into the whys and wherefores here, realize there is logic behind this choice.

Separate Clone and Open

The complicated method works with all versions of Fossil back to 2.1, and it is the one we recommend to people who want to get involved with the project, because it has numerous advantages over the easy methods. We’ll explain those benefits in the context of the MySQL++ project later, but for now, the method is:

$ mkdir -p ~/museum ~/src/mysqlpp/trunk
$ fossil clone ~/museum/mysqlpp.fossil
$ cd ~/src/mysqlpp/trunk
$ fossil open ~/museum/mysqlpp.fossil

Fossil Developer Access

If you have a developer account on the Fossil instance, just add your username to the URL like so:

$ fossil clone mysqlpp.fossil

If you’ve already cloned anonymously, simply tell Fossil about the new sync URL instead:

$ cd ~/src/mysqlpp/trunk
$ fossil sync

Either way, Fossil will ask you for the password for USERNAME on the remote Fossil instance, and it will offer to remember it for you. If you let it remember the password, operation from then on is scarcely different from working with an anonymous clone, except that on checkin, your changes will be sync’d back to the repository on if you’re online at the time, and you’ll get credit under your developer account name for the checkin.

If you’re working offline, Fossil will still do the checkin locally, and it will sync up with the central repository after you get back online. It is best to work on a branch when unable to use Fossil’s autosync feature, as you are less likely to have a sync conflict when attempting to send a new branch to the central server than in attempting to merge your changes to the tip of trunk into the current upstream trunk, which may well have changed since you went offline.

You can purposely work offline by disabling autosync mode:

$ fossil set autosync 0

Until you re-enable it (autosync 1) Fossil will stop trying to sync your local changes back to the central repo. In this mode, Fossil works more like Git’s default mode, buying you many of the same problems that go along with that working style. I recommend disabling autosync mode only when you are truly going to be offline and don’t want Fossil attempting to sync when you know it will fail.

Getting Developer Access

We are pretty open about giving developer access to someone who’s provided at least one good, substantial patch to the software. If we’ve accepted one of your patches, just ask for a developer account on the forum.

Working with Existing Tags and Branches

The directory structure shown in the separate clone and open sequence above is more complicated than strictly necessary, but it has a number of nice properties.

First, it collects software projects under a common top-level directory. I’ve used ~/src for this example, but you are free to use any scheme you like.

Second, the level underneath the project directory (~/src/mysqlpp) stores multiple separate checkouts, one for each version the developer is actively working with at the moment, so to add a few other checkouts, you could say:

~/museum/                  # Where one keeps fossils, right?
~/src/                     # Working tree for software projects
    mysqlpp/               # A directory for each project
        trunk/             # Primary working branch for MySQL++
        v2.3.2-modern/     # Checkout for another branch
        v3.2.3/            # Checkout for a tagged stable release

This gives you multiple independent checkouts, which allows you to quickly switch between versions with “cd” commands. The alternative (favored by Git and some other version control systems) is to use a single working directory and switch among versions by updating that single working directory in place. The problem is that this invalidates all of the build artifacts tied to changed files, so you have a longer rebuild time than simply switching among check-out directories. Since disk space is cheap these days, it’s better to have multiple working states and just “cd” among them.

When you say fossil update in a check-out directory, you get the “tip” state of that version’s branch. This means that if you created your “release” check-out while version 3.2.4 was current and you say “fossil update” today, you’ll get the release version 3.2.5 or later, because both tags are on the release branch. This shows an essential difference between tags and branches in Fossil, which are at bottom otherwise nearly identical: tags apply to a single commit only, while branches are propagating tags, moving from one commit to the next until explicitly canceled.

The project uses tags for each released version, and it has many working branches. You can use any of those names in “fossil open” and “fossil update” commands, and you can also use any of Fossil’s special check-in names.

Creating Branches

Creating a branch in Fossil is scary-simple, to the point that those coming from other version control systems may ask, “Is that really all there is to it?” Yes, really, this is it:

$ fossil ci --branch new-branch-name

That is to say, you make your changes as you normally would; then when you go to check them in, you give the --branch option to the ci/checkin command to put the changes on a new branch, rather than add them to the same branch the changes were made against.

While developers with login rights to the Fossil instance are allowed to check in on the trunk at any time, we recommend using branches whenever you’re working on something experimental, or where you can’t make the necessary changes in a single coherent checkin. A good example is an API or ABI breakage: those should go on a branch rather than on trunk, since they require discussion before we merge them down to trunk.

One of this project’s core principles is that trunk should always build without error, and it should always function correctly. That’s an ideal we have not always achieved, but we do always try to achieve it.

Contrast branches, which project developers may use to isolate work until it is ready to merge into the trunk. It is okay to check work in on a branch that doesn’t work, or doesn’t even build, so long as the goal is to get it to a point that it does build and work properly before merging it into trunk.

Here again we have a difference with Git: because Fossil normally syncs your work back to the central repository, this means we get to see the branches you are still working on. This is a good thing. Do not fear committing broken or otherwise bad code to a branch. You are not your code. We are software developers, too: we understand that software development is an iterative process, that not all ideas spring forth perfect and production-ready from the fingers of its developers. These public branches let your collaborators see what you’re up to; they may be able to lend advice, to help with the work, or to at least be unsurprised when your change finally lands in trunk.

Fossil fosters close cooperation, whereas Git fosters wild tangents that never come back home.

Jim McCarthy (author of Dynamics of Software Development) has a presentation on YouTube that touches on this topic at a couple of points:

Fossil’s sync-by-default behavior fights these negative tendencies.

Project developers are welcome to create branches at will. The main rule is to follow the branch naming scheme: all lowercase with hyphens separating words. See the available branch list for examples to emulate.

If you have checkin rights on the repository, it is generally fine to check things in on someone else’s feature branch, as long as you do so in a way that cooperates with the purpose of that branch. The same is true of trunk: you should not check something in directly on the trunk that changes the nature of the software in a major way without discussing the idea first. This is yet another use for branches: to make a possibly-controversial change so that it can be discussed before being merged into the trunk.

Special Branches

Most of the branches in the project are feature branches of the sort described in the previous section: an isolated line of development by one or more of the project’s developers to work towards some new feature, with the goal of merging that feature into the trunk branch.

There are a few branches in the project that are special, which are subject to different rules than other branches:

Discussion Forum

The “Forum” link at the top of the Fossil web interface is for both end-user discussions and internal MySQL++ project developer discussions. If you come across the old mailing list, we don’t use that any more. We also prefer Fossil forum and ticket postings to GitHub issues and such.

You can sign up for the forum without having a developer login, and you can even post anonymously. If you have a login, you can sign up for email alerts if you like.

Keep in mind that posts to the Fossil forum are treated much the same way as ticket submissions and wiki articles. They are permanently archived with the project. The “edit” feature of Fossil forums just creates a replacement record for a post, but the old post is still available in the repository. Don’t post anything you wouldn’t want made part of the permanent record of the project!

Bootstrapping the Library

When you check out MySQL++ from Fossil, there are a lot of things "missing" as compared to a distributed tarball, because the Fossil repository contains only source files, no generated files. The process that turns a fresh MySQL++ repository checkout into something you can build and hack on is called bootstrapping.

Boostrapping is best done on a modern Unix type platform: Linux, OS X, BSD, Solaris...any version released since 2005 or so.

It's possible to bootstrap MySQL++ on Windows, but it’s much harder.

Two of the tools you need to do this are commonly available on Unixy systems, at least as an option: Perl 5, and GNU Autoconf 1.59 or higher. If they're not installed, you can probably run your system's package manager to install suitable versions.

There's a third tool you'll need to bootstrap MySQL++ called Bakefile. The syntax used in mysql++.bkl requires at least Bakefile 0.2.5 or higher, which in turn requires Python 2.3 or higher to run. You may require a newer version of Bakefile to support newer OSes and Python versions; we've tested with versions up to 0.2.11 successfully.

Do not use any of the Bakefile 1.x versions: it’s an incompatible change, and we currently have no intention to switch from Bakefile 0.x.

Once you have all the tools in place, you can bootstrap MySQL++ with a Bourne shell script called bootstrap, which you get as part of the Fossil checkout. It's fairly powerful, with many options. For most cases, it suffices to just run it without any arguments:

$ ./bootstrap

For more unusual situations, here's the complete usage:

$ ./bootstrap [no{doc,ex,lib,opt}] [pedantic] [bat] [configure flags]


Bootstrapping the Library Using Only Windows

The thing that makes bootstrapping on Windows difficult is that one of the required steps uses a Unix-centric tool, Autoconf. This section gives alternatives for either getting Autoconf working on Windows or avoiding the need for it.

The thing Autoconf does that's relevant to Windows builds of MySQL++ is that it substitutes the current MySQL++ version number into several source files. This allows us to change the version number in just one place — — and have it applied to all these other places. Until you do this step, a Fossil checkout of MySQL++ won't build, because these files with the version numbers in them won't be generated.

Option 1: Copy the generated files over from a released version

Only one of these generated files is absolutely critical to allowing MySQL++ to build: lib/mysql++.h. So, the simplest option you have to bootstrap MySQL++ entirely on Windows is to copy lib/mysql++.h over from a released version of MySQL++. While you're doing that, you might copy over the other such generated files:


Having done that, you can complete the bootstrapping process by running bootstrap.bat. It has the same purpose as the Bourne shell script described above, but with a different and simpler usage:

C:\> bootstrap.bat [bakefile-options]

Any options passed are passed as-is to Bakefile. This is normally used to pass -D options to affect the generated build system output files.

Option 2: Cygwin

If you'd like to hack on MySQL++ entirely on Windows and have all the build freedoms enjoyed by those working on Unixy platforms, the simplest solution is probably to install Cygwin. It doesn’t matter whether you use the 32-bit or 64-bit version, for our purposes here.

While in the Cygwin setup program, you will have to add the Autoconf and Perl 5 packages, which aren't installed in Cygwin by default. Autoconf is in the Devel category, and Perl 5 in the Interpreters category.

You will also need to install the native Windows binary version of Bakefile. Don't get the source version and try to build Bakefile under Cygwin; it won't work. The Windows binary version of Bakefile includes an embedded version of Python, so you won't need to install Cygwin's Python.

Having done all this, you can follow the Unix bootstrapping instructions in the previous section.

Option 3: Windows Subsystem for Linux (WSL)

If you’re on Windows 10, you have the option of installing WSL, a lightweight Linux kernel and user environment that runs atop Windows. This is fundamentally different technology than Cygwin, but the user-level effect of it is the same as far as MySQL++’s build system goes.

Assuming you use the default Ubuntu enviroment atop WSL, the standard bootstrapping process applies, after you install the needed tools:

$ sudo apt install build-essential perl libmysqlclient-dev

You will also need to install the legacy Bakefile 0.2.x version. If there is a bakefile package available at all, it is likely for the incompatible 1.x series.

Option 4: "Here's a nickel, kid, get yourself a better computer."

Finally, you might have access to a Unixy system, or the ability to set one up. You don't even need a separate physical computer, now that virtual machine techology is free.

Given such a machine, you'd do the Fossil checkout of MySQL++ on that machine, then bootstrap it there using the instructions in the previous section, and copy the generated files back to the Windows box.

Manipulating the Build System Source Files

One of the things the bootstrapping system described above does is produces various types of project and make files from a small number of source files. This system lets us support many platforms without having to maintain separate build system files for each platform.

Bakefile produces most of these project and make files from a single source file called mysql++.bkl.

Except for small local changes, it's best to change mysql++.bkl and "re-bake" the project and make files rather than change those files directly. You can do this with the bootstrap scripts covered above. On Windows, if all you've changed is mysql++.bkl, you can use rebake.bat instead, which doesn't try to do as much as bootstrap.bat.

Bakefile produces finished project files for Visual C++ and Xcode and finished Makefiles for MinGW. It also produces, which is input to GNU Autoconf along with and config/*. You may need to change these latter files in addition to or instead of mysql++.bkl to get the effect you want. Running bootstrap incorporates changes to all of these files in the GNU Autoconf output.

While Bakefile's documentation isn't as comprehensive as it ought to be, you can at least count on it to list all of the available features. So, if you can't see a way to make Bakefile do something, it's likely it just can't do it. Bakefile is a high-level abstraction of build systems in general, so it'll never support all the particulars of every odd build system out there.

Submitting Patches

If you do not have a developer login on the project repository, you can still send changes to the project.

The simplest way is to say this after developing your change against trunk:

$ fossil diff > my-changes.patch

Then paste that into a forum post using a fenced code block. We will also accept trivial patches not needing discussion as text or attachments on a Fossil ticket.

If you're making a patch against a MySQL++ distribution tarball, you can generate a patch this way:

$ diff -ruN mysql++-olddir mysql++-newdir > mychange.patch

The diff command is part of every Unix and Linux system, and should be installed by default. If you're on a Windows machine, GNU diff is part of Cygwin and WSL. Fossil is also available for all of these systems. There are no excuses for not being able to make unified diffs. :)

Bundles Instead of Patches

If your change is more than a small patch, fossil diff might not incorporate all of the changes you have made. The old unified diff format can’t encode branch names, file renamings, file deletions, tags, checkin comments, and other Fossil-specific information. For such changes, it is better to send a Fossil bundle:

$ fossil set autosync 0                # disable autosync
$ fossil checkin --branch my-changes
  ...followed by more checkins on that branch...
$ fossil bundle export --branch my-changes my-changes.bundle

After that first fossil checkin --branch ... command, any subsequent fossil ci commands will check your changes in on that branch without needing a --branch option until you explicitly switch that checkout directory to some other branch. This lets you build up a larger change on a private branch until you’re ready to submit the whole thing as a bundle.

Because you are working on a branch on your private copy of the project’s Fossil repository, you are free to make as many checkins as you like on the new branch before giving the bundle export command.

Once you are done with the bundle, upload it somewhere public and point to it from a forum post or ticket.

Contribution Licensing

Because MySQL++ uses the “viral” LGPL license, you do not have to declare a release of copyright or explicit license: a public diff against our source base is inherently made available under the same license.

Can I Use GitHub Instead?

Although MySQL++ does have a GitHub mirror, it is intended as a read-only mirror for those heavily tied into Git-based tooling. You’re welcome to send us a PR anyway, but realize that what’s going to happen on the back end is that we’ll generate a patch, apply it to the Fossil repo by hand, test it, and then commit it to the repository under one of our existing Fossil developer accounts. Only then do we update the mirror so that the change appears on GitHub; thus, you don’t get GitHub credit for the PR. You avoid these problems by simply asking for a developer account on the Fossil repo, so you can commit there instead.

This is not simply because setting up bidirectional mirroring is difficult, it is actually impossible to achieve 100% fidelity due to limitations of Git and/or GitHub. If you want a faithful clone of the project repo, or if you wish to contribute to the project’s development with full credit for your contributions, it’s best done via Fossil, not via GitHub.

The MySQL++ Code Style

Every code base should have a common code style. Love it or hate it, here are MySQL++'s current code style rules:

Source Code

File types: ac, cpp, h, in, m4, pl

XML/HTML Dialects

File types: bkl, dbx, hta

Plain Text Files

File types: txt

When in doubt, mimic what you see in the current code. When still in doubt, ask on the forum.

Testing Your Proposed Change

MySQL++ includes a self-test mechanism called dtest. It's a Bourne shell script, run much like exrun:

$ ./dtest [-s server_addr] [-u user] [-p password]

This automatically runs most of the examples, captures the outputs to a file, and then compares that to a known-good run's outputs, stored in bmark.txt. So, before you submit a patch, run dtest to see if anything has changed. If something has and you can't account for it, it represents a problem that you'll have to fix before submitting the patch. If it gives an expected change, remove bmark.txt, re-run dtest, and include the bmark.txt diffs in your patch. This communicates to us the fact that you know there are differences and want the patch evaluated anyway. Otherwise, we are likely to view the change in the program outputs as a bug or regression.

dtest also runs all of the unit tests in test/*. The purpose of test/* is different from that of examples/*:

Patches should include tests if they introduce new functionality or fix a bug that the existing test coverage failed to catch. If the test is noisy, needs DB access, or tests multiple parts of the library at once, it goes in examples/*. If your change affects only one class in MySQL++ and testing it can be done without instantiating other MySQL++ classes — other than by composition, of course — it should go in test/*.

In general, prefer modifying an existing examples/* or test/* program. Add a new one only if you're introducing brand new functionality or when a given feature currently has no test at all.

Beware that the primary role of the examples is to illustrate points in the user manual. If an existing example does something similar to what a proper test would need to do and the test doesn't change the nature of the example, don't worry about changing the example code. If your test would change the nature of the example, you either need to do the test another way or also submit a change to doc/userman/*.dbx that incorporates the difference.

Adding Support for a Different Compiler

As described above, MySQL++ uses the Bakefile system for creating project files and makefiles. This allows a single change to propagate across all build systems we support. In the past, we used more ad-hoc systems, and we'd frequently forget to update the build system for a particular platform, so that at any given time, at least one target was likely to be broken. We will therefore resist any change that requires that we go back to distributing manually-maintained build system files not generated from a single source.

If MySQL++ doesn't currently ship with project files or makefiles tuned for your compiler of choice, you need to work through the Bakefile mechanism to add support. We're not willing to do ad-hoc platform support any more, so please don't ask if you can send us project files instead; we don't want them.

If you want to port MySQL++ to another platform, we need to be confident that the entire library works on your platform before we'll accept patches. In the past, we've had broken ports that were either missing important library features, or which crashed when built in certain ways. Few people will knowingly use a crippled version of MySQL++, since there are usually acceptable alternatives. Therefore, such ports become maintenance baggage with little compensating value.

Maintaining a Private Repository

Although Fossil tries to sync changes back to the MySQL++ Fossil repository by default, it is possible to maintain a private repository that simply pulls changes in occasionally.

The first step is to turn off the auto-sync feature:

 $ fossil set autosync off

...or set it so it only pulls from the central repo without trying to push local changes, making it complain that you don’t have commit capability:

 $ fossil set autosync pullonly

Then I recommend that you make any local changes on a branch:

...hack, hack, hack...
$ fossil ci --branch my-local-branch

After you give the --branch option on a checkin, Fossil automatically switches your local checkout to that branch, so that all further checkins can be made without the --branch option. To get back to the trunk, you'd say fossil up trunk, but under this workflow, the need for that will be rare.

When something happens on the official trunk on that you want pulled into your private repository, say:

$ fossil pull
$ fossil merge trunk

The first command pulls all remote changes into your local clone, but since those changes don't affect your private branch, you won't see any immediate change. The second attempts to merge the trunk branch's changes since the last branch or merge point into your private branch.

Whether the merge is successful or not, Fossil does not immediately modify your clone, only the working checkout directory. You must then say fossil ci once you're happy with the merge. Until then, all the usual Fossil commands like fossil diff and fossil status will help you come to that decision.

If you ever decide to contribute your private branch to the MySQL++ project, there are a couple of easy ways to achieve that. Ask about it on the forum if you find yourself in this situation.

If you want to ensure that your private branch never syncs with the public project, even if you later get a developer account on it, you can go a step further and use Fossil’s private branch feature.