Compilation errors in templates don't get reported but cause a NullReferenceException

[niekschoemaker]

Bug description

When using custom T4 templates any compilation errors in the templates cause a NullReferenceException because the HandleErrors is only called after processing the templates, and not right after compilation.

The call should be used after both the compilation step and the processing step, as the template will be null if compilation fails, causing the NullReferenceException instead of a clear compilation error message.

Your code

Simply follow the guide to use the default templates from here: https://learn.microsoft.com/en-us/ef/core/managing-schemas/scaffolding/templates?tabs=dotnet-core-cli#adding-the-default-templates

After this create any compilation error in this template (in my case it was a missing using)

Stack traces

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.TextTemplatingModelGenerator.GenerateModel(IModel model, ModelCodeGenerationOptions options)
   at UA.Uniform.Db.Scaffolder.Scaffolding.Internal.TextTemplatingModelGenerator.GenerateModel(IModel model, ModelCodeGenerationOptions options) in D:\pas\ua\ua.uniform\tools\source\UA.Uniform.Db.Scaffolder\Scaffolding\Internal\TextTemplatingModelGenerator.cs:line 21
   at Microsoft.EntityFrameworkCore.Scaffolding.Internal.ReverseEngineerScaffolder.ScaffoldModel(String connectionString, DatabaseModelFactoryOptions databaseOptions, ModelReverseEngineerOptions modelOptions, ModelCodeGenerationOptions codeOptions)
   at Microsoft.EntityFrameworkCore.Design.Internal.DatabaseOperations.ScaffoldContext(String provider, String connectionString, String outputDir, String outputContextDir, String dbContextClassName, IEnumerable`1 schemas, IEnumerable`1 tables, String modelNamespace, String contextNamespace, Boolean useDataAnnotations, Boolean overwriteFiles, Boolean useDatabaseNames, Boolean suppressOnConfiguring, Boolean noPluralize)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContextImpl(String provider, String connectionString, String outputDir, String outputDbContextDir, String dbContextClassName, IEnumerable`1 schemaFilters, IEnumerable`1 tableFilters, String modelNamespace, String contextNamespace, Boolean useDataAnnotations, Boolean overwriteFiles, Boolean useDatabaseNames, Boolean suppressOnConfiguring, Boolean noPluralize)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContext.<>c__DisplayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)

Verbose output

EF Core version

9.0.10

Database provider

not applicable

Target framework

.NET 9.0

Operating system

Windows 11

IDE

CLI and Rider 2025.2.3