Franky's Notes: Utiliser des template T4 avec des paramètres c'est possible

Dernièrement j'ai voulu à développer une petite application pour générer du code. L’idée est bien simple je voulais avoir une interface me permettant de saisir quelques informations et ensuite… le code devait se généré.

Après quelques recherches, mon choix s’est porté sur Text Template Transformation Toolkit (T4) de Microsoft. Le générateur de code utilisant les T4 est inclus dans Visual Studio 2008. Donc même si rien n’est nécessaire, je conseille fortement le T4 Editor de Clarius Consulting qui affichera le code avec quelques couleurs. La version de la communauté est gratuite, la version complète est payante… on s’en doutait ;)

Créer un template simple

Il y a plusieurs excellents tutoriels expliquent comment utiliser les templates T4, notamment sur les blogs de Oleg Sych et Scott Hanselman. Mais pour faire vite, voici un tout petit exemple.

Dans un projet Visual Studio, cliquer sur [Project] –> [Add new Item].
- Vous pouvez sélectionner
  - La catégorie [Code Generation] et le template [File].
  - La catégorie [General] et le template [Text File]. Dans ce cas assurez-vous spécifier l’extension “.tt”.
Entrez le nom de votre fichier, cliquez le bouton [Add]
Le fichier à été ajouté a votre projet. Double cliquez dessus.
À la fin du fichier ajoutez le code suivant: Nous sommes le: <#= DataTime.Now.TimeOfDay #>
Votre fichier devrait ressembler à:

        1: <#@ template language="C#" hostspecific="True" debug="True" #>

       2: <#@ output extension="txt" #>

       3: 

       4: <#

       5: // <copyright file="File1.tt" company="">

       6: //  Copyright © . All Rights Reserved.

       7: // </copyright>

       8:  

       9:  

      10: #>

      11:  

      12: Nous sommes le: <#= DateTime.Now.TimeOfDay #>

Pour voir le texte généré, il faut développer (expand) le noeud du fichier et double cliquer sur le sous-fichier.

Voilà!

Utiliser des paramètres

Il est possible de créer des templates statique ou dynamique. Pour mon projet je voulais pouvoir passer des paramètres à la dernière seconde, donc mon template ce devait d’être dynamique. Dans un des post de Oleg Sych ce dernier spécifie qu’un Custom Host doit être fait pour pouvoir passer des paramètres. Cependant je n’ai pu trouver plus de détails… Afin de faire profiter d’autre personne de mon experience j’ai décider d’écrire ce billet.

Voici donc comment j’y suis parvenu.

Objectifs

En partant du “Hello world” classique je vais le personaliser pour dire bonjour à une personne en particulier. Le nom de cette personne sera le paramètre.

Avant de commencer

Tout d’abord afin de pouvoir faire le Custom Host il faut avoir accès au namespace Microsoft.VisualStudio.TextTemplating qui se trouve dans le VS2880 SDK. Donc il faut installer le Visual Studio 2008 SDK (s’il n’est pas présent sur votre poste).

Custom Host

Pour faire le Custom Host j’ai simplement pris le code de Microsoft, il servira de classe de base.

       1: //CustomT4EngineHost.cs

       2:  

       3: using System;

       4: using System.Collections.Generic;

       5: using System.Linq;

       6: using System.Text;

       7: using Microsoft.VisualStudio.TextTemplating;

       8: using System.CodeDom.Compiler;

       9: using System.IO;

  

namespace CustomT4

{

    //The text template transformation engine is responsible for running 

    //the transformation process.

    //The host is responsible for all input and output, locating files, 

    //and anything else related to the external environment.

    //-------------------------------------------------------------------------

    [Serializable]

    public class CustomT4EngineHost : MarshalByRefObject, ITextTemplatingEngineHost

    {

  

  

        //the path and file name of the text template that is being processed

        //---------------------------------------------------------------------

        public string TemplateFile

        {

            get { return ""; }

        }

  

  

        //This will be the extension of the generated text output file.

        //The host can provide a default by setting the value of the field here.

        //The engine can change this value based on the optional output directive

        //if the user specifies it in the text template.

        //---------------------------------------------------------------------

        private string fileExtensionValue = ".txt";

        public string FileExtension

        {

            get { return fileExtensionValue; }

        }

  

  

        //This will be the encoding of the generated text output file.

        //The host can provide a default by setting the value of the field here.

        //The engine can change this value based on the optional output directive

        //if the user specifies it in the text template.

        //---------------------------------------------------------------------

        private Encoding fileEncodingValue = Encoding.UTF8;

        public Encoding FileEncoding

        {

            get { return fileEncodingValue; }

        }

  

        //These are the errors that occur when the engine processes a template.

        //The engine passes the errors to the host when it is done processing,

        //and the host can decide how to display them. For example, the host 

        //can display the errors in the UI or write them to a file.

        //---------------------------------------------------------------------

        private CompilerErrorCollection errorsValue;

        public CompilerErrorCollection Errors

        {

            get { return errorsValue; }

        }

  

  

        //The host can provide standard assembly references.

        //The engine will use these references when compiling and

        //executing the generated transformation class.

        //--------------------------------------------------------------

        public IList<string> StandardAssemblyReferences

        {

            get

            {

                return new string[]

                {

                    //If this host searches standard paths and the GAC,

                    //we can specify the assembly name like this.

                    //---------------------------------------------------------

                    //"System"

  

                    //Because this host only resolves assemblies from the 

                    //fully qualified path and name of the assembly,

                    //this is a quick way to get the code to give us the

                    //fully qualified path and name of the System assembly.

                    //---------------------------------------------------------

                    typeof(System.Uri).Assembly.Location

                };

            }

        }

  

  

        //The host can provide standard imports or using statements.

        //The engine will add these statements to the generated 

        //transformation class.

        //--------------------------------------------------------------

        public IList<string> StandardImports

        {

            get

            {

                return new string[]

                {

                    "System"

                };

            }

        }

  

  

        //The engine calls this method based on the optional include directive

        //if the user has specified it in the text template.

        //This method can be called 0, 1, or more times.

        //---------------------------------------------------------------------

        //The included text is returned in the context parameter.

        //If the host searches the registry for the location of include files,

        //or if the host searches multiple locations by default, the host can

        //return the final path of the include file in the location parameter.

        //---------------------------------------------------------------------

        public bool LoadIncludeText(string requestFileName, out string content, out string location)

        {

            content = System.String.Empty;

            location = System.String.Empty;

  

            //If the argument is the fully qualified path of an existing file,

            //then we are done.

            //----------------------------------------------------------------

            if (File.Exists(requestFileName))

            {

                content = File.ReadAllText(requestFileName);

                return true;

            }

  

            //This can be customized to search specific paths for the file.

            //This can be customized to accept paths to search as command line

            //arguments.

            //----------------------------------------------------------------

            else

            {

                return false;

            }

        }

  

  

        //Passes in the name of a service. If you have that service, you need to 

        //pass back a pointer to it. Otherwise, you need to pass back NULL to 

        //indicate that you have no knowledge of that service.

        //--------------------------------------------------------------------

        public object GetHostOption(string optionName)

        {

            object returnObject;

            switch (optionName)

            {

                case "CacheAssemblies":

                    returnObject = true;

                    break;

                default:

                    returnObject = null;

                    break;

            }

            return returnObject;

        }

  

  

        //The engine calls this method to resolve assembly references used in

        //the generated transformation class project and for the optional 

        //assembly directive if the user has specified it in the text template.

        //This method can be called 0, 1, or more times.

        //---------------------------------------------------------------------

        public string ResolveAssemblyReference(string assemblyReference)

        {

            //If the argument is the fully qualified path of an existing file,

            //then we are done. (This does not do any work.)

            //----------------------------------------------------------------

            var _assemblyRef = assemblyReference;

            if (_assemblyRef.EndsWith(".dll", StringComparison.InvariantCultureIgnoreCase))

                _assemblyRef = _assemblyRef.Remove(_assemblyRef.Length - 4);

            if (_assemblyRef.EndsWith(".exe", StringComparison.InvariantCultureIgnoreCase))

                _assemblyRef = _assemblyRef.Remove(_assemblyRef.Length - 4);

  

            foreach (var _assembly in AppDomain.CurrentDomain.GetAssemblies())

            {

                var _assemblyName = _assembly.GetName();

                if (String.Compare(_assemblyName.Name, _assemblyRef, true) == 0 ||

                    String.Compare(_assemblyName.FullName, _assemblyRef, true) == 0)

                    return _assembly.Location;

            }

            if (File.Exists(assemblyReference))

            {

                return assemblyReference;

            }

  

            //Maybe the assembly is in the same folder as the text template that 

            //called the directive.

            //----------------------------------------------------------------

            string candidate = Path.Combine(Path.GetDirectoryName(this.TemplateFile), assemblyReference);

            if (File.Exists(candidate))

            {

                return candidate;

            }

  

            //This can be customized to search specific paths for the file

            //or to search the GAC.

            //----------------------------------------------------------------

  

            //This can be customized to accept paths to search as command line

            //arguments.

            //----------------------------------------------------------------

  

            //If we cannot do better, return the original file name.

            return "";

        }

  

  

        //The engine calls this method based on the directives the user has 

        //specified in the text template.

        //This method can be called 0, 1, or more times.

        //---------------------------------------------------------------------

        public Type ResolveDirectiveProcessor(string processorName)

        {

            //This host will not resolve any specific processors.

  

            //Check the processor name, and if it is the name of a processor the 

            //host wants to support, return the type of the processor.

            //---------------------------------------------------------------------

            if (string.Compare(processorName, "XYZ", StringComparison.OrdinalIgnoreCase) == 0)

            {

                //return typeof();

            }

  

            //This can be customized to search specific paths for the file

            //or to search the GAC

  

            //If the directive processor cannot be found, throw an error.

            throw new Exception("Directive Processor not found");

        }

  

  

        //A directive processor can call this method if a file name does not 

        //have a path.

        //The host can attempt to provide path information by searching 

        //specific paths for the file and returning the file and path if found.

        //This method can be called 0, 1, or more times.

        //---------------------------------------------------------------------

        public string ResolvePath(string fileName)

        {

            if (fileName == null)

            {

                throw new ArgumentNullException("the file name cannot be null");

            }

  

            //If the argument is the fully qualified path of an existing file,

            //then we are done

            //----------------------------------------------------------------

            if (File.Exists(fileName))

            {

                return fileName;

            }

  

            //Maybe the file is in the same folder as the text template that 

            //called the directive.

            //----------------------------------------------------------------

            string candidate = Path.Combine(Path.GetDirectoryName(this.TemplateFile), fileName);

            if (File.Exists(candidate))

            {

                return candidate;

            }

  

            //Look more places.

            //----------------------------------------------------------------

            //More code can go here...

  

            //If we cannot do better, return the original file name.

            return fileName;

        }

  

  

        //If a call to a directive in a text template does not provide a value

        //for a required parameter, the directive processor can try to get it

        //from the host by calling this method.

        //This method can be called 0, 1, or more times.

        //---------------------------------------------------------------------

        public string ResolveParameterValue(string directiveId, string processorName, string parameterName)

        {

            if (directiveId == null)

            {

                throw new ArgumentNullException("the directiveId cannot be null");

            }

            if (processorName == null)

            {

                throw new ArgumentNullException("the processorName cannot be null");

            }

            if (parameterName == null)

            {

                throw new ArgumentNullException("the parameterName cannot be null");

            }

  

            //Code to provide "hard-coded" parameter values goes here.

            //This code depends on the directive processors this host will interact with.

  

            //If we cannot do better, return the empty string.

            return String.Empty;

        }

  

  

        //The engine calls this method to change the extension of the 

        //generated text output file based on the optional output directive 

        //if the user specifies it in the text template.

        //---------------------------------------------------------------------

        public void SetFileExtension(string extension)

        {

            //The parameter extension has a '.' in front of it already.

            //--------------------------------------------------------

            fileExtensionValue = extension;

        }

  

  

        //The engine calls this method to change the encoding of the 

        //generated text output file based on the optional output directive 

        //if the user specifies it in the text template.

        //----------------------------------------------------------------------

        public void SetOutputEncoding(System.Text.Encoding encoding, bool fromOutputDirective)

        {

            fileEncodingValue = encoding;

        }

  

  

        //The engine calls this method when it is done processing a text

        //template to pass any errors that occurred to the host.

        //The host can decide how to display them.

        //---------------------------------------------------------------------

        public void LogErrors(CompilerErrorCollection errors)

        {

            errorsValue = errors;

        }

  

  

        //This is the application domain that is used to compile and run

        //the generated transformation class to create the generated text output.

        //----------------------------------------------------------------------

        public AppDomain ProvideTemplatingAppDomain(string content)

        {

            //This host will provide a new application domain each time the 

            //engine processes a text template.

            //-------------------------------------------------------------

            return AppDomain.CreateDomain("Generation App Domain");

  

            //This could be changed to return the current appdomain, but new 

            //assemblies are loaded into this AppDomain on a regular basis.

            //If the AppDomain lasts too long, it will grow indefintely, 

            //which might be regarded as a leak.

  

            //This could be customized to cache the application domain for 

            //a certain number of text template generations (for example, 10).

  

            //This could be customized based on the contents of the text 

            //template, which are provided as a parameter for that purpose.

        }

  

    }

    

}

L’idée est d’avoir une classe host dans laquel on pourra passer notre paramètre. Comme on ne peut pas modifier la classe CustomHost on fera une classe qui hérite de Custom Host et qui implemente notre interface dans où le paramètre est défini.

Ensuite nous avons besoin d’une classe qui définisse notre parameter: CustomT4Parameter.

       1: //CustomT4Parameter.cs

       2:  

       3: using System;

       4: using System.Collections.Generic;

       5: using System.Linq;

       6: using System.Text;

       7:  

       8: namespace CustomT4

       9: {

      10:     [Serializable]

      11:     public class CustomT4Parameter

      12:     {

      13:         public CustomT4Parameter() {}

      14:  

      15:         private string _Name;

      16:  

      17:         public string Name

      18:         {

      19:             get { return _Name; }

      20:             set { _Name = value; }

      21:         }

      22:     }

      23: }

Afin de faire notre classe host qui nous servira dans notre projet, nous avons besoin d’un Interface qui permetera d’avoir accès à notre paramètre.

       1: //ICustomT4Host.cs

       2:  

       3: using System;

       4: using System.Collections.Generic;

       5: using System.Linq;

       6: using System.Text;

       7:  

       8: namespace CustomT4

       9: {

      10:     public interface ICustomT4Host

      11:     {

      12:         CustomT4Parameter T4Parameter { get; }

      13:     }

      14: }

Rien de bien compliqué…

       1: //T4Host.cs

       2:  

       3: using System;

       4: using System.Collections.Generic;

       5: using System.Linq;

       6: using System.Text;

       7:  

       8:  

       9: namespace CustomT4

{

    [Serializable]

    public class T4Host : CustomT4EngineHost, ICustomT4Host 

    {

        private CustomT4Parameter _T4Parameter;

  

        public T4Host(CustomT4Parameter param)

        {

            _T4Parameter = param;

        }

  

        #region Members

  

        public CustomT4Parameter T4Parameter

        {

            get { return _T4Parameter; }

        }

  

        #endregion

    }

}

Maintenant, il nous faut un template. Afin d’accèder à notre paramètre il faut inclure une propriété: T4Param. Une fois ce “Getter” fait nous pouvons avois accès aux propriété du paramètre simplement: <#= T4Param.Name #>

       1: //Hello.tt

       2:  

       3: <#@ template language="C#" hostspecific="True"  #>

       4: <#@ assembly name="System.dll" #>

       5: <#@ assembly name="PlayWithT4.exe" #>

       6: <#@ import namespace="CustomT4" #>

       7: // <autogenerated>

       8: // This code was generated by a tool. Any changes made manually will be lost

       9: // the next time this code is regenerated.

// </autogenerated>

  

using System;  

  

public class Hello<#= T4Param.Name #>

{

   public static void SayHello()

   {

      Console.WriteLine("Hello <#= T4Param.Name #>!");

   }

}

  

<#+

    CustomT4Parameter T4Param

    {

        get { 

            ICustomT4Host _host = Host as ICustomT4Host;

            if(_host != null)

               return _host.T4Parameter;

            else

               throw new InvalidOperationException("Expected to find a ClassEntry");

        }

    }

#>

Tout est prêt, il reste seulement à faire l’appel de l’engine et lui passant le custom host et le template. Je me suis fais un petit Helper histoire de garder le code de la forms le plus simple possible, mais ce n’est pas nécessaire…

       1: // TextTemplateHelper.cs

       2:  

       3: using System;

       4: using System.IO;

       5: using Microsoft.VisualStudio.TextTemplating;

       6: using System.Globalization;

       7:  

       8: namespace CustomT4

       9: {

    [Serializable]

    public class TextTemplateHelper

    {

        public static void ProcessTemplate(string templateFileName, string outputFileName)

        {

            ProcessTemplate(templateFileName, outputFileName, new CustomT4EngineHost());

        }

  

        public static void ProcessTemplate(string templateFileName, string outputFileName, CustomT4EngineHost host)

        {

            string templateDirectory = Path.GetDirectoryName(templateFileName);

            string outputFilePath = Path.Combine(templateDirectory, outputFileName);

  

            string template = File.ReadAllText(templateFileName);

            Engine engine = new Engine();

            string output = engine.ProcessTemplate(template, host);

  

            if (host.Errors.HasErrors)

                throw new InvalidOperationException(String.Format(CultureInfo.InvariantCulture, "Cannot generate template {0}. {1} Error(s). First error is: {2}", templateFileName, host.Errors.Count, host.Errors[0]));

            else

                File.WriteAllText(outputFileName, output, host.FileEncoding);

        }

    }

}