What is the '.tt' extension?

Question

I work with a bunch of something.js.tt JavaScript files using Knockout and a bunch of something-else.tt HTML files.

The infrastructure is mostly a C backend with Perl serving API and we use these .tt files to show the HTML and .js.tt to serve the Knockout.js code. What is .tt?

Answer 1

If you take a look inside the file, you'll probably notice a lot of logic injecting things. This is because this kind of files are used to generate other files.

As explained in the MS page shared by @Recev Yildiz:

In Visual Studio, a T4 text template is a mixture of text blocks and control logic that can generate a text file.

The control logic is written as fragments of program code in Visual C# or Visual Basic. In Visual Studio 2015 Update 2 and later, you can use C# version 6.0 features in T4 templates directives.

The generated file can be text of any kind, such as a web page, or a resource file, or program source code in any language.

There are two kinds of T4 text templates: run time and design time.

Here's an example of a code I've got from a Entity Framework file, from a ASP.NET Web Application (.NET Framework) project (MVC design):

<#@ template language="C#" debug="false" hostspecific="true"#>
<#@ include file="EF6.Utility.CS.ttinclude"#><#@
 output extension=".cs"#><#

const string inputFile = @"DBModel.edmx";
var textTransform = DynamicTextTransformation.Create(this);
var code = new CodeGenerationTools(this);
var ef = new MetadataTools(this);
var typeMapper = new TypeMapper(code, ef, textTransform.Errors);
var loader = new EdmMetadataLoader(textTransform.Host, textTransform.Errors);
var itemCollection = loader.CreateEdmItemCollection(inputFile);
var modelNamespace = loader.GetModelNamespace(inputFile);
var codeStringGenerator = new CodeStringGenerator(code, typeMapper, ef);

var container = itemCollection.OfType<EntityContainer>().FirstOrDefault();
if (container == null)
{
    return string.Empty;
}
#>
//------------------------------------------------------------------------------
// <auto-generated>
// <#=CodeGenerationTools.GetResourceString("Template_GeneratedCodeCommentLine1")#>
//
// <#=CodeGenerationTools.GetResourceString("Template_GeneratedCodeCommentLine2")#>
// <#=CodeGenerationTools.GetResourceString("Template_GeneratedCodeCommentLine3")#>
// </auto-generated>
//------------------------------------------------------------------------------

<#

var codeNamespace = code.VsNamespaceSuggestion();
if (!String.IsNullOrEmpty(codeNamespace))
{
#>
namespace <#=code.EscapeNamespace(codeNamespace)#>
{
<#
    PushIndent("    ");
}

#>
using System;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
<#
if (container.FunctionImports.Any())
{
#>
using System.Data.Entity.Core.Objects;
using System.Linq;
<#
}
#>

<#=Accessibility.ForType(container)#> partial class <#=code.Escape(container)#> : DbContext
{
    public <#=code.Escape(container)#>()
        : base("name=<#=container.Name#>")
    {
<#
if (!loader.IsLazyLoadingEnabled(container))
{
#>
        this.Configuration.LazyLoadingEnabled = false;
<#
}

foreach (var entitySet in container.BaseEntitySets.OfType<EntitySet>())
{
    // Note: the DbSet members are defined below such that the getter and
    // setter always have the same accessibility as the DbSet definition
    if (Accessibility.ForReadOnlyProperty(entitySet) != "public")
    {
#>
        <#=codeStringGenerator.DbSetInitializer(entitySet)#>
<#
    }
}
#>
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }

<#
    foreach (var entitySet in container.BaseEntitySets.OfType<EntitySet>())
    {
#>
    <#=codeStringGenerator.DbSet(entitySet)#>
<#
    }

    foreach (var edmFunction in container.FunctionImports)
    {
        WriteFunctionImport(typeMapper, codeStringGenerator, edmFunction, modelNamespace, includeMergeOption: false);
    }
#>
}

The file was way larger than what you see here. And as you can see, it seems to be a really busy code.

This is the context where the file is placed:

Answer 2

Text Template Transformation Toolkit, shortly written as T4, uses the .tt file extension for its source files. It is Microsoft's template-based text generation framework included with Visual Studio.

For more info, see the docs.

Answer 3

A TT file is a Visual Studio Text Template, developed by Microsoft.