UKHO.GitHubCopilot.ToolKit: Instructions file for GitHub Copilot

C# development guidelines

Overview

These instructions define baseline default rules for writing and changing C# code in this repository. The goal is consistent style, safe nullability, predictable error handling, and changes that remain testable.

Scope

Applies to: **/*.cs

• These rules apply to all C# files under src/ and test/.
• These rules are repository defaults for C# work unless a narrower file or an explicitly documented exception applies.
• When a work item needs a justified deviation from these defaults, document the reason in the relevant project or work-package documentation so the deviation remains reviewable.
• For test code, also follow /.github/instructions/tests.instructions.md and (when applicable) /.github/instructions/playwright.instructions.md.
• For auth-related work, also follow /.github/instructions/auth.instructions.md.

Instructions

MUST

• Follow formatting rules defined in .editorconfig.

• Keep one top-level class, interface, record, struct, enum, or delegate per file.

• Name each C# file to match its top-level type.

• Use the C# language version already configured by the repository.

  • Do not change LangVersion (or rely on preview language features) as part of feature work unless the work item explicitly requires it.

• Follow naming conventions:

  • Use PascalCase for classes, records, structs, enums, delegates, methods, positional record parameters, and public members.
  • Use camelCase for local variables.
  • Use camelCase for class and struct primary constructor parameters.
  • Prefix interface names with I.
  • Use singular names for enums unless they represent flags values.
  • Do not use Enum, Flag, or Flags suffixes in enum type names.
  • Name classes, records, and structs with nouns or noun phrases.

• Write null-safe code:

  • Respect nullable reference types annotations.
  • Prefer non-nullable types and validate inputs at boundaries.
  • Prefer is null / is not null pattern checks.