How do you get T4ReferencePath to work?

Question

I've beat my head against the wall for a couple of days on this one. No amount of Googling or messing around seems to yield the answer.

I want to run a T4 template at build time. In it, I need to access types in an assembly that I've built before this project. I need msbuild to be able to build it, and msbuild doesn't play nice with VS variables, so I need to use another means to load the assembly.

I've read in a lot of places that T4ReferencePath is the answer to setting up a place to load a custom assembly from. However, I cannot get it to work.

When I specify this:

<T4ReferencePath Include="$(TargetDir)" />

I get this when I either try to load the project in VS or run it with msbuild:

d:\Users\250894\Documents\Visual Studio 2013\Projects\TestT4\TestT4.csproj(90,22): error MSB4066: The attribute "Include" in element <T4ReferencePath> is unrecognized.

I do have the "Visual Studio Visualization and Modeling SDK" installed.

I apologize for the lack of brevity, but I'm including the entire .csproj file of my test project in case something is glaringly obvious that I've missed. I'm not including my .tt file because it isn't relevant if I can't even get my csproj to load. If I exclude the T4ReferencePath, then things work correctly.

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <ProjectGuid>{5B9944E7-47CF-4BFE-BAEF-F02D29D59E80}</ProjectGuid>
    <OutputType>Exe</OutputType>
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <RootNamespace>TestT4</RootNamespace>
    <AssemblyName>TestT4</AssemblyName>
    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
    <FileAlignment>512</FileAlignment>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
    <PlatformTarget>AnyCPU</PlatformTarget>
    <DebugSymbols>true</DebugSymbols>
    <DebugType>full</DebugType>
    <Optimize>false</Optimize>
    <OutputPath>bin\Debug\</OutputPath>
    <DefineConstants>DEBUG;TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
    <PlatformTarget>AnyCPU</PlatformTarget>
    <DebugType>pdbonly</DebugType>
    <Optimize>true</Optimize>
    <OutputPath>bin\Release\</OutputPath>
    <DefineConstants>TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
  </PropertyGroup>
  <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Debug|x64'">
    <DebugSymbols>true</DebugSymbols>
    <OutputPath>bin\x64\Debug\</OutputPath>
    <DefineConstants>DEBUG;TRACE</DefineConstants>
    <DebugType>full</DebugType>
    <PlatformTarget>x64</PlatformTarget>
    <ErrorReport>prompt</ErrorReport>
    <CodeAnalysisRuleSet>MinimumRecommendedRules.ruleset</CodeAnalysisRuleSet>
    <Prefer32Bit>true</Prefer32Bit>
  </PropertyGroup>
  <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Release|x64'">
    <OutputPath>bin\x64\Release\</OutputPath>
    <DefineConstants>TRACE</DefineConstants>
    <Optimize>true</Optimize>
    <DebugType>pdbonly</DebugType>
    <PlatformTarget>x64</PlatformTarget>
    <ErrorReport>prompt</ErrorReport>
    <CodeAnalysisRuleSet>MinimumRecommendedRules.ruleset</CodeAnalysisRuleSet>
    <Prefer32Bit>true</Prefer32Bit>
  </PropertyGroup>
  <ItemGroup>
    <Reference Include="System" />
    <Reference Include="System.Core" />
    <Reference Include="System.Xml.Linq" />
    <Reference Include="System.Data.DataSetExtensions" />
    <Reference Include="Microsoft.CSharp" />
    <Reference Include="System.Data" />
    <Reference Include="System.Xml" />
  </ItemGroup>
  <ItemGroup>
    <Compile Include="Program.cs" />
    <Compile Include="Properties\AssemblyInfo.cs" />
    <Compile Include="Test.cs">
      <AutoGen>True</AutoGen>
      <DesignTime>True</DesignTime>
      <DependentUpon>Test.tt</DependentUpon>
    </Compile>
  </ItemGroup>
  <ItemGroup>
    <None Include="App.config" />
    <None Include="Test.tt">
      <Generator>TextTemplatingFileGenerator</Generator>
      <LastGenOutput>Test.cs</LastGenOutput>
    </None>
  </ItemGroup>
  <ItemGroup>
    <Service Include="{508349B6-6B84-4DF5-91F0-309BEEBAD82D}" />
  </ItemGroup>
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
  <PropertyGroup>
    <!-- Get the Visual Studio version – defaults to 12: -->
    <VisualStudioVersion Condition="'$(VisualStudioVersion)' == ''">12.0</VisualStudioVersion>
    <!-- Keep the next element all on one line: -->
    <VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>
    <TransformOnBuild>true</TransformOnBuild>
    <IncludeDslT4Settings>true</IncludeDslT4Settings>
    <T4ReferencePath Include="$(TargetDir)" />
  </PropertyGroup>
  <Import Project="$(VSToolsPath)\TextTemplating\Microsoft.TextTemplating.targets" />
</Project>

Answer 1

I finally stumbled onto the answer. I can't imagine that no one has run into this before, but here we are. Hopefully, I've blazed a trail that will help those who come after.

In spite of what common sense tells me, T4ReferencePath is not a "Property". It's an "Item". When I removed it from the "PropertyGroup" and added it to an "ItemGroup", it got happy.

One of the blights of software development and computer use in general is unhelpful error messages. I can't say that this is the most egregious example I've ever encountered, but it's up there.