How to get enum type in a T4 template

Question

In the process of writing a T4 text template I ran into an issue I'm struggling to get by. I need to know the type of the enum I'm processing.

I have enums that are based on byte and ushort. I need the T4 text template to write code to cast the enum to the correct value type in order to serialize the enum and put it into a byte array.

This is an example enum of type byte

namespace CodeEnumType
{
    public enum MyEnum : byte
    {
        Member1 = 0,
        Member2 = 1,
    }
}

And this is my T4 text template

<#@ template hostspecific="true" language="C#" #>
<#@ output extension=".cs" #>
<#@ assembly name="EnvDte" #>
<#@ import namespace="EnvDTE" #>
<#@ import namespace="System.Collections.Generic" #>
<#
var serviceProvider = this.Host as IServiceProvider;
var dte = serviceProvider.GetService(typeof(DTE)) as DTE;
var project = dte.Solution.FindProjectItem(this.Host.TemplateFile).ContainingProject as Project;
var projectItems = GetProjectItemsRecursively(project.ProjectItems);
foreach(var projectItem in projectItems)
{
    var fileCodeModel = projectItem.FileCodeModel;
    if(fileCodeModel == null)
    {
        continue;
    }

    CodeElements codeElements = fileCodeModel.CodeElements;
    ProcessCodeElements(codeElements);
}
#>
<#+
public void ProcessCodeElements(CodeElements codeElements)
{
    if(codeElements == null)
    {
        return;
    }

    foreach(CodeElement codeElement in codeElements)
    {
        switch(codeElement.Kind)
        {
            case vsCMElement.vsCMElementNamespace:
                CodeNamespace codeNamespace = codeElement as CodeNamespace;
                CodeElements childCodeElements = codeNamespace.Members;
                ProcessCodeElements(childCodeElements);
                break;
            case vsCMElement.vsCMElementEnum:
                CodeEnum codeEnum = codeElement as CodeEnum;
                WriteLine(codeEnum.Name);
                //
                // here I would like the enum type
                //
                break;
        }
    }
}
public IEnumerable<ProjectItem> GetProjectItemsRecursively(ProjectItems items)
{
    if(items == null)
    {
        yield break;
    }

    foreach(ProjectItem item in items)
    {
        yield return item;

        var childItems = GetProjectItemsRecursively(item.ProjectItems);
        foreach(ProjectItem childItem in childItems)
        {
            yield return childItem;
        }
    }
}
#>

Notice the part where I wrote

        //
        // here I would like the enum type
        //

Here I have my enum information in the variable codeEnum and this is where my problem is. How do I get byte or ushort type from codeEnum?

I'm not using Reflection here as Type.GetType() does not work well if the assembly have not been compiled.

Answer 1

The underlying enum type is not exposed by the EnvDTE object model. As a workaroud, you can retrieve the source code of the enum type definition and parse out the base type, e.g. using a regular expression:

foreach(CodeElement codeElement in codeElements)
{
    switch(codeElement.Kind)
    {
        case vsCMElement.vsCMElementNamespace:
            CodeNamespace codeNamespace = codeElement as CodeNamespace;
            CodeElements childCodeElements = codeNamespace.Members;
            ProcessCodeElements(childCodeElements);
            break;
        case vsCMElement.vsCMElementEnum:
            CodeEnum codeEnum = codeElement as CodeEnum;
            Write(codeEnum.Name);

            // get the source code of the enum
            string sourceCodeEnum = 
                codeEnum.StartPoint.CreateEditPoint().GetText(codeEnum.EndPoint);

            // a regular expression capturing the base type
            System.Text.RegularExpressions.Regex regex 
                = new System.Text.RegularExpressions.Regex(
                    @"\benum .*\s*\:\s*(?<underlyingType>\w*)");

            var match = regex.Match(sourceCodeEnum);
            if (match.Success)
            {
                WriteLine(" : " + match.Groups["underlyingType"].Value);
            }

            break;
    }
}

Note that the regex in the sample is just a very simple pattern that might need to be adjusted to cope with different source code formatting.