Launch condition to ensure that 64-bit installer is used on 64-bit system

Question

What's up with my launch condition? It's supposed to prevent the x86 installer from running on a 64-bit system, but it seems to have no effect.

<!-- Launch Condition to check that x64 installer is used on x64 systems -->
<Condition Message="64-bit operating system was detected, please use the 64-bit installer.">
  <![CDATA[VersionNT64 AND ($(var.Win64) = "no")]]>
</Condition>

var.Win64 is derived from the MSBuild variables like this:

  <!-- Define platform-specific names and locations -->
  <?if $(var.Platform) = x64 ?>
  <?define ProductName = "$(var.InstallName) (x64)" ?>
  <?define Win64 = "yes" ?>
  <?define PlatformProgramFilesFolder = "ProgramFiles64Folder" ?>
  <?define PlatformCommonFilesFolder = "CommonFiles64Folder" ?>
  <?else ?>
  <?define ProductName = "$(var.InstallName) (x86)" ?>
  <?define Win64 = "no" ?>
  <?define PlatformProgramFilesFolder = "ProgramFilesFolder" ?>
  <?define PlatformCommonFilesFolder = "CommonFilesFolder" ?>
  <?endif ?>

I would like to solve my problem, but I'd also be interested to hear about strategies for troubleshooting this type of problem.

Answer 1

According to the LaunchCondition table definition:

Expression that must evaluate to True for installation to begin.

Your condition consists of 2 parts: the first one evaluates at install time, the other one evaluates at build time. So, for x86 package the second part of condition will evaluate to "no" = "no" at build time, which obviously gives True at install time. And the first part - VersionNT64 - is defined (and thus, True) on x64 machines. That's why the whole condition is True and installation starts.

You can rewrite your condition as follows:

<Condition Message="64-bit operating system was detected, please use the 64-bit installer.">
  <?if $(var.Win64) = "yes" ?>
    VersionNT64
  <?else?>
    NOT VersionNT64
  <?endif?>
</Condition>

Hence, in 64-bit package the condition will be just VersionNT64, and will pass and start install. Form x86 package the condition will be NOT VersionNT64, which will obviously fail on 64-bit, but start on 32-bit.