Experience Sitecore !

I was recently investigating gulp file of Habitat for interesting goodies and came across taskApply-Xml-Transform, so decided to dig deeper into the one.

What it does?

It looks within all Foundation, Feature and Project layers for config transformations (*.xdt files) in order to run each of them and transform into target Sitecore web.config from the web root folder.

What is XDT?

In very simple, XDT is just an XML file with a set of rules of what and how to transform within web.comfig. We may use them in cases when we need to somehow transform web.config outside of <sitecore> node of configuration so that we can't rely on config paths that only apply within the <sitecore> node. XDT structure corresponds to the structure of target web.config file with additional commands coming from XML-Document-Transform XML namespace. Below is an example of such XDT file, that adds Microsoft.Codedom compiler references into web.config in case they don't exist:

<?xml version="1.0" encoding="utf-8"?>
<configuration  xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
  <system.codedom xdt:Transform="InsertIfMissing">
    <compilers xdt:Transform="InsertIfMissing">
      <compiler xdt:Transform="InsertIfMissing" xdt:Locator="Match(language)" language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701" />
      <compiler xdt:Transform="InsertIfMissing" xdt:Locator="Match(language)" language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" />
    </compilers>
  </system.codedom>
</configuration>

I wanted to see how exactly it's being triggered, so running script in a verbose mode, brought me to the following conclusion:

How does it run?

So, configuration transform relies on msbuild to do this job. But instead of Debug, Release or Clean targets, it uses a target calledApplyTransform It accepts numerous parameters, among those we have XDT file to transform, target folder, target configuration file to be transformed and few other parameters. Entire call extracted from a batch looks like below:

C:\Program Files\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin\amd64\MSBuild.exe 
/nologo /maxcpucount /nodeReuse:False 
/property:Configuration=Debug 
/property:Platform="Any CPU" 
/property:WebConfigToTransform=C:\inetpub\wwwroot\Platform.dev.local\ 
/property:TransformFile=C:\Platform\src\Feature\Accounts\code\App_Config\Web.config.xdt 
/property:FileToTransform=App_Config\Security\Domains.config 
/target:ApplyTransform 
/toolsversion:15.0 
/verbosity:diagnostic 
C:\Projects\Platform\scripts\applytransform.targets

You may modify the code above and run it on your own casual day-to-day activities outside of gulp, Habitat and other tools.

Hope this helps!