Test plan for "required members"

[jcouv]

Championed proposal: dotnet/csharplang#3630
Specification: https://github.com/dotnet/csharplang/blob/main/proposals/csharp-11.0/required-members.md

Compiler

• Notify F#, C++/CLI, etc.
• VB (disallow attribute usage? tracking issue Required Members VB Support #61435)
• update test plan
• Review public API
• Any breaking changes? (parsing issues?)
• SyntaxNormalizer
• SymbolDisplay
• address PROTOTYPE markers
• local named "required" in top-level statements (C# 10 vs 11), will be handled as bug fix after merge (issue Local named "required" in top-level statements #61510)
• make type named "required" an error
• consider filtering RequiredMembers attribute in compiler layer/API (issue Consider filtering RequiredMembers attribute in compiler layer/API #61511)

declaration

• required as contextual keyword ("required" type, type parameter, etc exists in scope)
• where required modifier is allowed/disallowed
• disallow required modifier based on LangVer
• disallow required type name based on LangVer
• missing attribute type or ctor
• RequiredMember attribute emitted on type and members
• Overriding can tighten requirement
• Cannot hide required member
• Required member must as accessible as containing type
• RequiredMember attribute disallowed in source
• field/property without setter
• field/property with less accessible setter
• different kinds of members (field, property, indexer, event, nested type, ...)
• different kinds of containing types (class, struct, record; disallow interface)
• required with field/property initializer (allowed)
• rules with obsolete
• no definite assignment for SetsRequired
• must specify SetsRequired when SetsRequired on base or this
• combination with other modifiers (fixed, ref readonly, ref, const, static disallowed; others such as extern, partial, virtual allowed)
• record with required positional member declared explicitly
• modifier can be parsed in different orders

metadata

• Required attribute cannot be manually applied
• required members are marked Required and the type too. But not if merely derived from a type with required members.
• CompilerFeatureRequired with marker string
• Obsolete with marker string
• invalid type from metadata
• SetsRequired set on record copy ctor

usage

• object initialization
• nested object initializers new C { Inner = new D { ... } } versus new C { Inner = { ... } }
• attribute construction with named arguments
• new() constraint not satisfied

nullability

• nullable analysis of constructors in presence or absence of [SetsRequiredMembers] with required members
• initial nullable flow state of required setters, when the type contains some combination of required and non-required non-nullable reference properties.

LDM

• LDM: should we give a diagnostic for required property with an initializer (useless)? (answer: no, can be useful)
• LDM: should we do something about ref-returning properties (useless)? (disallow)
• LDM: should we do something about readonly modifier? (disallow)
• LDM: what if the required property is obsolete?

BCL

• Confirm we want types in BCL and complete API review
• Implement types (Add attributes for required members runtime#64287)
• Can/should Reflection APIs honor required?

Productivity:

• typing/completion
  • Partial doesn't trigger soft select in override completion #61439 covers soft-select during override completion, also broken for partial.
• override completion
• MetadataAsSource (done)
• formatting
• colorization
• F1/help (done)
• QuickInfo (P0: should not crash, P2: consider whether to show required) (no change, manually verified)
• Sorting modifiers (done)
• completion of object creation should call out required members
• snippet-style completion?
• some existing refactorings produce/modify constructors
• add option to generate required property for refactorings that generate properties

[hez2010]

Any updates for record with required positional member declared explicitly? Will this land in C# 11?

[333fred]

I'm not sure what you're asking about. This issue is tracking adding tests.

[hez2010]

I'm not sure what you're asking about. This issue is tracking adding tests.

See https://sharplab.io/#v2:EYLgtghglgdgPgAQEwEYCwAoTAnApgYwHtsATAAgDFDCAKPARwFco9zYAXMgDQEoBuIA

We still cannot use required in primary constructor of records.

[333fred]

We still cannot use required in primary constructor of records.

For new additions to the feature, please use csharplang.

However, for this particular request, I'll save you some time by telling you that you don't really want it. If you mark a property as required, it must be set with a property initializer. No ifs, ands, or buts. This would create a primary constructor that takes a parameter to set the property, and you must then use an object initializer to set the property again.

[jcouv]

@jasonmalinowski I think we're ready to close this test plan from the compiler side. The follow-up compiler work is tracked by separate issues.
Can you create follow-up issues for bullets that still need IDE work?

[jcouv]

@333fred will follow-up with runtime team on possibility of Reflection API and file an issue if there's interest.
Chatted with @jasonmalinowski about remaining IDE items. I think all the basics are covered and there's no urgent follow-up.
I'll go ahead and close this test plan as completed. Thanks