chore(template): sync with dailydevops/dotnet-template [skip ci]

Author: samtrion

.github/instructions/csharp.instructions.md

@@ -0,0 +1,66 @@
+---
+applyTo: '**/*.cs'
+
+description: 'This file contains instructions for C# development.
+  It includes guidelines for using GitHub Copilot, managing dependencies, and following coding standards.
+  Ensure to follow the practices outlined in this file to maintain code quality and consistency.'
+---
+
+# C# Development Instructions
+
+## General
+
+* The project MUST use the latest version C#, currently C# 13 features.
+* MUST follow standard C# coding conventions (naming, indentation, spacing).
+* MUST implement robust error handling with try-catch blocks and meaningful messages.
+* MUST write unit tests for all critical functionalities.
+* MUST always review AI-generated code for correctness, security, and performance.
+
+## Code Style
+
+Follow these C# coding conventions for consistency across the project.
+
+* MUST use `var` when the type is obvious from the right side of the assignment.
+* MUST use `Argument.ThrowIfNull(x)` instead of `if (x == null) throw new ArgumentNullException(nameof(x))`, when nuget package `NetEvolve.Arguments` is referenced.
+* MUST use `ArgumentNullException.ThrowIfNull(x)` instead of `if (x == null) throw new ArgumentNullException(nameof(x))`, when nuget package `NetEvolve.Arguments` is not referenced.
+
+## Formatting
+
+Apply code-formatting style defined in `.editorconfig`.
+
+* MUST prefer file-scoped namespace declarations and single-line using directives.
+* MUST insert a newline before the opening curly brace of any code block (e.g., after `if`, `for`, `while`, `foreach`, `using`, `try`, etc.).
+* MUST ensure that the final return statement of a method is on its own line.
+* MUST use pattern matching and switch expressions wherever possible.
+* MUST use `nameof` instead of string literals when referring to member names.
+* MUST ensure that XML doc comments are created for any public APIs. When applicable, include `<inheritdoc />` for derived members.
+
+## Arrays and Collections
+
+* MUST prefer `Enumerable.Empty<T>()` or `Array.Empty<T>()` over `null` returns.
+
+## Nullable Reference Types
+
+Declare variables non-nullable, and check for `null` at entry points.
+
+* MUST always use `is null` or `is not null` instead of `== null` or `!= null`.
+* MUST trust the C# null annotations and don't add null checks when the type system says a value cannot be null.
+* MUST apply `NotNullAttribute` and other nullable attributes for any public APIs.
+
+## Testing
+
+* MUST prefer to use [TUnit](https://github.com/thomhurst/TUnit) with [Microsoft.Testing.Platform](https://learn.microsoft.com/dotnet/core/testing/microsoft-testing-platform-intro).
+* If TUnit is not available, MUST use [XUnit](https://xunit.net/).
+* MUST NOT emit `Act`, `Arrange` or `Assert` comments.
+* MUST NOT use any mocking framework at the moment.
+* MUST copy existing style in nearby files for test method names and capitalization.
+
+## Build and test AI-generated code
+
+1. Build from the root with `dotnet build <solutionfile>.slnx`.
+2. If that produces errors, fix those errors and build again. Repeat until the build is successful.
+3. Run tests with `dotnet test <solutionfile>.slnx`.
+4. If tests fail, analyze the failures and fix the code. Do not ignore failing tests.
+5. Verify that all new code has appropriate test coverage.
+6. Run a final build to ensure everything compiles successfully after all changes.
+