EasyMercurial

h1. OS/X version, hardware platform, and Qt version compatibility

*Executive summary:* For a program like EasyHg that demands the widest possible compatibility, we currently want to hit the following targets:

* 10.4 PPC 32-bit Carbon

* 10.4 Intel 32-bit Carbon

* 10.6 Intel 64-bit Cocoa

To do this, we currently need at least two builds of Qt:

* 10.6 gcc-4.2 Cocoa x86_64

* 10.4 gcc-4.0 Carbon PPC and i386

This currently means the Qt 4.7.1 default distribution plus a separate Carbon build will do.

Note it is not possible to cover all platforms in a single build step, we always need to do at least two separate builds plus lipo.

If we are going to make a 3-way universal binary, we need to ensure the 10.4 build gets selected for i386 -- i.e. to pull only the x86_64 architecture from any 10.5 or 10.6 SDK build we do.  The inability to select between different i386 versions from a single universal binary is a strong incentive to stick to a single 10.4+ Carbon build for all 32-bit platforms.

h2. OS/X 10.6

h3. As target

* By far the most common version as of Feb 2011 (apparently >80%)

* Not supported on PPC

* Runs in 64-bit mode by default where possible

* Note Python is also 64-bit by default, so PyQt needs to be as well

* Is _not_ always 64-bit -- it is supported on 32-bit-only hardware such as Core Duo (first Intel Macs)

h3. As build host

* Builds 64-bit by default

* Can be used to do 32-bit Intel and PPC builds

h2. OS/X 10.5

h3. As target

* Not all that much more widely used than 10.4 -- if we were dropping 10.4, we probably might as well drop 10.5 as well

* Last version supported for PPC platforms

* Runs in 32-bit mode by default

* Can build for it from 10.5, 10.6

* Requires SDK @/Developer/SDKs/MacOSX10.5.SDK@

* First version to support Objective-C 2.0

* Qt Cocoa supported

h3. As build host

* Builds 32-bit by default

* Can be used to do 64-bit builds

h2. OS/X 10.4

h3. As target

* Oldest version still apparently in use as of Feb 2011: not very widespread (low single digit %age of Mac users), but at least two researchers here use it

* Appears in PPC and i386 systems

* Runs in 32-bit mode only

* Can build for it from 10.4, 10.5, 10.6

* Requires SDK @/Developer/SDKs/MacOSX10.4u.SDK@

* Requires @-mmacosx-version-min=10.4@ on 10.5+

* Requires gcc-4.0 to be requested explicitly on 10.6

* Does not support Objective-C 2.0

* Not a supported target for Qt's Cocoa builds, Qt Carbon needed

h3. As build host

* Does not support Objective-C 2.0

* 10.4u SDK can be used to build 64-bit executables of simple C/C++ programs such as plugins, but not of GUIs or anything using Core frameworks

h2. Special note about Python

Python versioning and compatibility is a bit of a nightmare.  The system Python is 2.5 on 10.4/10.5 and 2.6 on 10.6 -- OK so far.  On 10.6, Python is 32-/64-bit universal which runs in 64-bit by default on a 64-bit system, so any modules need to be available both ways as well (troubleshooting this when it goes wrong is quite tricky).  There is an environment variable @VERSIONER_PYTHON_PREFER_32_BIT@ which you can set to cause it always to run in 32-bit.

Where things get complicated is when users install additional versions of Python from other ports repositories; this seems to be quite common around these parts.  Then your user-installed Python is likely to get picked up before the system one, and you don't know whether it's going to be 32- or 64-bit, and it won't support the versioning environment variable.  My impression is that people get custom Python installs dragged in as dependencies of other packages, and that tends to break quite a lot of things.

Some 10.6 system Pythons have a problem loading modules, apparently something getting broken during the upgrade from 10.5 -- this affects my home machine, but I haven't had time to look into it properly yet.