Test Plan for Partial Events and Constructors

[jjonescz]

Champion issue: dotnet/csharplang#9058
Speclet: https://github.com/dotnet/csharplang/blob/main/proposals/partial-events-and-constructors.md
Feature branch: https://github.com/dotnet/roslyn/tree/features/PartialEventsCtors

• language version (LangVersion)
  • partial event
  • constructor: partial treated as type previously
• partial modifier location
  • after event
  • after accessibility modifier
  • on accessors
• in non-partial class or struct (NotInPartialType)
• in interface (InInterface*)
• missing implementation or declaration (Missing*)
• duplicate implementation or declaration (Duplicate*)
• static constructor (StaticPartialConstructor_*)
• constructor initializer: this, base (ConstructorInitializers_)
• primary constructor (PrimaryConstructor_*)
  • with constructor initializer
• extern (Extern_*)
• abstract (Abstract)
• explicit interface implementation event (ExplicitInterfaceImplementation)
• partial event in interface:
  • should not be abstract
  • should be virtual unless explicitly sealed Partial default interface members are not virtual #77346
• event initializers (EventInitializer_*)
  • multiple declarators and initializers
• missing accessors (EventAccessorMissing)
• Windows runtime event (WinRtEvent)
• attributes (Attributes*)
  • combined from parts
  • duplicate diagnostics
  • event attribute targets
  • ObsoleteAttribute
  • SkipLocalsInitAttribute (AttributeTests_WellKnownAttributes.SkipLocalsInit_*Event*)
  • caller-info attributes apply from definition only
  • nullable attributes
• mismatched signatures (Difference_*)
  • static and instance
  • accessibility
  • event type
  • parameter type, ref kind, name, scoped, params, default parameter value
  • tuple element names (Difference_*Type)
  • nullability
  • unsafe
  • virtual, override, sealed, new
• partial event is not field-like
  • no backing field (Metadata)
  • use +=, -=, but not as a value (Use_EventAsValue)
• defining declaration used for: (Difference_ParameterNames)
  • lookup
  • metadata emit
• doc comments (DocumentationCommentCompilerTests.PartialEvent_*, PartialConstructor_*)
  • on one or both parts
  • invalid comments
  • paramref when parameter names differ
• public API: Public API for partial events #77203
  • IEventSymbol.*Partial*
  • GetDeclaredSymbol
• breaking change (ReturningPartialType_*)
  • documentation: see Compiler Breaking Changes - DotNet 10.md
• EE: evaluate partial constructor
• EnC: changes to partial implementation