Sprint 4: To block or not to block

Our goal is to block our package from running on a Server edition of Windows. Windows Installer has launch conditions, which allow us to implement the blocking behavior that we're looking for, but launch conditions aren't technically blockers. Instead, launch conditions are intended to be taken literally: Conditions that must be met to launch the package. If the condition is not met, a message is shown (blocking the package). So, from a purely pedantic perspective, launch conditions are not blockers, they're not not blockers. In pseudo-code, it works like this:

IF launch_condition = FALSE THEN
  SHOW launch_condition_message
ENDIF

It's a little backward because the launch condition message doesn't match the launch condition expression.

But wait. We discovered that the blocker condition we wanted is MsiNTProductType <> 1 (MsiNTProductType <> 1 in XML) but to turn it into a launch condition, we want the opposite. The opposite of <> is =, so the launch condition expression we want is MsiNTProductType = 1.

Yes, MSI has a NOT operator, so you could, if you're feeling that way, express the launch condition as NOT (MsiNTProductType <> 1). That's definitely not at all confusing. Stick with the = and avoid the < and > XML weirdness.

Back to the pseudo-code, it would look like this:

IF (MsiNTProductType = 1) = FALSE THEN
  SHOW launch_condition_message
ENDIF

Now let's write some WiX code.