How can I set the WiX installer version to the current build version?

Question

You could use Product/@Version="!(bind.FileVersion.FileId)" (replace FileId with the Id of the file from which you'd like to get the version number) and light.exe will populate the value with the version of the file referenced by the FileId.

I did this in one of my projects by writing a preprocessor extension to read the file version from my executable. So the WiX file looks something like:

<?define ProductName="$(fileVersion.ProductName($(var.MyApp.TargetPath)))" ?>
<?define CompanyName="$(fileVersion.CompanyName($(var.MyApp.TargetPath)))" ?>
<?define ProductVersion="$(fileVersion.ProductVersion($(var.MyApp.TargetPath)))" ?>
<Product 
    Id="<product ID>" 
    Name="$(var.ProductName)" 
    Version="$(var.ProductVersion)" 
    Manufacturer="$(var.CompanyName)" 
    Language="1033" 
    UpgradeCode="<upgrade code>">

I've posted the code for in on CodePlex: http://wixfileversionext.codeplex.com/

In case someone is looking for an actual XML example, this works with .NET assemblies (and you don't have to do the Assembly or KeyPath attributes). I eliminated unrelated code with [...] place holders:

<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
    <Product [...] Version="!(bind.fileVersion.MyDLL)">
        [...]
        <Directory Id="TARGETDIR" Name="SourceDir">
            <Directory Id="ProgramFilesFolder" Name="PFiles">
                <Directory Id="INSTALLDIR" Name="MyDLLInstallLocation">
                    <Component Id="MainLib" Guid="[...]">
                        <File Id="MyDLL" Name="MyDll.dll" Source="MyDll.dll" />
                        [...]
                    </Component>
                    [...]
                </Directory>
            </Directory>
        </Directory>
    </Product>
</Wix>

Here's a very simple way to get your Bootstrapper Bundle Version to match your MyApp AssemblyVersion using a BeforeBuild Target and DefineConstants.

Bundle.wxs:

<Bundle Name="$(var.ProductName) Bootstrapper v$(var.BuildVersion)"
     Version="$(var.BuildVersion)"

Bootstrapper.wixproj:

<Target Name="BeforeBuild">
  <GetAssemblyIdentity AssemblyFiles="..\MyApp\bin\$(Configuration)\MyApp.exe">
    <Output TaskParameter="Assemblies" ItemName="AssemblyVersion" />
  </GetAssemblyIdentity>
  <PropertyGroup>
    <DefineConstants>BuildVersion=%(AssemblyVersion.Version)</DefineConstants>
  </PropertyGroup>
</Target>