Hacking on MySQL++

If you are going to make any changes to MySQL++, this file has some hints and commentary you may find helpful.

Code Repository Access

MySQL++ uses the Fossil distributed version control system. See its quick start guide if you are unfamilar with Fossil.

That Fossil repository is also mirrored to GitHub nightly, but this is a read-only mirror, meant for use with Git automation tooling. For example, you could use MySQL++ as a submodule in a larger Git project via this channel. Changes to MySQL++ still must go go through the Fossil repository.

You must be running Fossil version 2.1 or higher to access the MySQL++ repository. If your operating system includes an older Fossil package, you will either have to install an official binary or build it from source.

To clone the MySQL++ repository anonymously, say:

$ fossil clone mysqlpp.fossil

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

$ fossil clone mysqlpp.fossil

That will get you a file called mysqlpp.fossil containing the abridged version history of MySQL++ back to the project's founding.

The repository clone file can be named anything you like. Even the .fossil extension is just a convention, not a requirement.

To "open" the repo clone so you can hack on it, say:

$ mkdir mysqlpp
$ cd mysqlpp
$ fossil open ../mysqlpp.fossil

This two step “clone and open” process may seem weird if you’re used to Git, but it’s a feature. It means the repository and working directories are separate, allowing you to create multiple independent checkouts from a single repo clone. I like a working tree that looks like this:

~/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

You check out a branch or tag like so:

$ cd ~/src/mysqlpp/v3.2.3
$ fossil open ~/museum/mysqlpp.fossil v3.2.3

Fossil will let you make any modifications you like to your local repository copy. For those with check-in privileges on the upstream copy, changes get automatically synced with it by default. (If you prefer Git or Mercurial style two-phase commits, you can say fossil set autosync off, then later say fossil push after making one or more checkins.) If you don't have commit capability on the central repository server, checkins just modify your local repository clone. If you do such checkins on a branch, you don’t need to worry about conflicts when pulling down upstream changes into your local clone.

Developers are expected to make all changes that affect the libary's API, ABI, or behavior on a branch, rather than check such changes directly into the trunk. Once we have discussed the change on the forum and resolved any isssues with the experimental branch, it will be merged into the trunk.

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 checkin --branch new-branch-name

That is to say, you make your changes as you normally would; then when you go to make the first checkin, you give the --branch option to put the changes on a new branch, rather than add them to the same branch the changes were made against. Every subsequent checkin without a --branch option gets checked in as the new tip of that branch.

If you’re creating a branch that will probably live a long enough time that you’ll want to return to trunk one or more times while that branch lives, you might follow the above command with a sequence like this:

$ fossil update trunk           # return working dir to tip-of-trunk
$ mkdir ../new-branch-name
$ cd ../new-branch-name
$ fossil open ~/museum/mysqlpp.fossil new-branch-name

Now you can bounce back and forth between trunk and your new branch with a simple cd command, rather than switching in place, as is typical with Git. This style of work avoids invalidating build system outputs, and it makes it possible to switch branches without checking in or stashing your work on the other branch first.

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 do it on Windows, but much harder; we cover the options below in a separate section.

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:

$ apt install bakefile build-essential perl libmysqlclient-dev

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.

On 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 wish to submit a patch to the library, it’s probably simplest to paste it into a forum post, if it’s small. If it’s large, put it in Pastebin or similar, then link to it from a forum post. We want patches in unified diff format.

We will also accept trivial patches not needing discussion as text or attachments to a Fossil ticket.

The easiest way to get a unified diff is to check out a copy of the current MySQL++ tree as described above. Then make your change, cd to the MySQL++ root directory, and ask Fossil to generate the patch for you:

$ fossil diff > mychange.patch

If your patch adds new files, moves files, or needs to be understood in terms of multiple checkins, it's best to do that work on a private local branch, then send a bundle instead of a patch.

If you've sent patches to MySQL++ before and don't have a Fossil developer login, another alternative is to ask for a login before you begin work so that your changes are automatically sync'd to the main Fossil repository as you work, so you don't have to send bundles or patch files. We generally don't refuse such requests if you've already proven your ability to work productively with the MySQL++ project.

If you're making a patch against a MySQL++ distribution tarball, then 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. Fossil is also available for all of these systems. There are no excuses for not being able to make unified diffs. :)

Although MySQL++ does have a GitHub mirror, we do not acccept PRs via that channel, because the mirror is read-only. You can still send us a PR through GitHub, but realize that what’s going to happen on the back end is that we’ll generate a patch and apply it to the Fossil repo by hand, then update the mirror, so you won’t get GitHub credit for the PR. Sorry; there’s no easy way for this mirroring system to accept contributions back the other direction. If you want credit for the commit, ask us for an account on the Fossil repo, and commit it there instead.

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 as a bug.

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 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 us to make changes to a single set of files, and have the proper changes be made to all generated project files and makefiles. In the past, we used more ad-hoc systems, and we'd frequently forget to update individual project files and makefiles, so at any given time, at least one target was likely to be broken.

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 missing important library features, or that 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 syncs changes back to the MySQL++ Fossil repository by default, it is possible to maintain a private copy that simply pulls changes in occasionally.

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

 $ fossil set autosync off

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 sync
$ 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.