Web Deployment Projects targeting x64

I am working on an ASP.NET web application which has mixed-mode C++/CLI dependencies that call out to pure unmanaged DLLs. A new requirement is a 64-bit version of the application (it runs fine on Win64 in a IIS 32-bit app pool, but since 32-bit mode is an all-or-nothing proposition, it was decided we need a true 64 bit app.)

I ran into a problem getting the Visual Studio Web Deployment Project to compile my app. It seems that aspnet_compiler.exe loads all of the dependencies during compilation, and the 32 bit compiler cannot load the 64 bit images (you get a "bad image format" error.) This is true even on Win64 build machines that have the .NET Framework64 (and therefore the 64-bit aspnet_compiler.exe)

After a bit of spelunking through the .wdproj, I found that a relatively simple change to the MSBUILD file shipped with the WD project will allow this to work out. It simply forces MSBUILD to use the 64 bit compiler if the $(Platform) variable is set to "x64"

Here is how to do it:

1. Find the install directory for the Web Deployment Project MSBUILD scripts. On my system, this is:
   c:\Program Files (x86)\MSBuild\Microsoft\WebDeployment\v9.0
2. Edit (or better yet, edit a copy) of Microsoft.WebDeployment.targets.
   
   Change this section of the file (around line 524 of the source in the version I have):
   
   

   <PropertyGroup>
     <PrecompDependsOn>
       _PrepareForBuild;
     </PrecompDependsOn>
     <AspNetToolPath Condition=" '$(Platform)' == 'x64'">$(windir)\Microsoft.NET\Framework64\$(FrameworkVersion)</AspNetToolPath></PropertyGroup>
   
   <Target Name="AspNetCompiler" DependsOnTargets="$(PrecompDependsOn)">
       <AspNetCompiler
         PhysicalPath="$(_AspNetCompilerSourceWebPath)"
         TargetPath="$(TempBuildDir)"
         VirtualPath="$(_AspNetCompilerVirtualPath)"
         Force="$(_Force)"
         Debug="$(DebugSymbols)"
         Updateable="$(EnableUpdateable)"
         KeyFile="$(_FullKeyFile)"
         KeyContainer="$(_AspNetCompilerKeyContainer)"
         DelaySign="$(DelaySign)"
         AllowPartiallyTrustedCallers="$(AllowPartiallyTrustedCallers)"
         FixedNames="$(_AspNetCompilerFixedNames)"
         Clean="$(Clean)"
         MetabasePath="$(_AspNetCompilerMetabasePath)"
         ToolPath="$(AspNetToolPath)"/>

   I added the definition of the AspNetToolPath property, which points to the .NET Framework64 directory. I also added the ToolPath attribute to the AspNetCompiler element, and set its value to be the value of my AspNetToolPath property. Note that ToolPath will be blank if $(Platform) is something other than x64, which will result in the default 32 bit compiler being used.