Test plan for default

[cston]

Test plan for default

Checklist for implementation of https://github.com/dotnet/csharplang/blob/master/proposals/target-typed-default.md

General concerns

• Backward compatibility: report version error with earlier /langversion
• Semantic model behavior
  • GetSymbolInfo
  • GetSpeculativeSymbolInfo
  • GetTypeInfo
  • GetSpeculativeTypeInfo
  • GetConstantValue
  • AnalyzeDataFlow
  • ClassifyConversion

Type and members

• Attributes: positional and named parameters
• Parameters:
  • Default parameter values: CancellationToken ct = default
  • params:
    • F(params T[] args): F(default) and F(null, default)
    • overload resolution with params and non-params, mixed value/reference types
• Constant values
• Enum (implicit and explicit underlying type)
• Expression trees
• Iterators: yield return default;
• Initializers (object, collection, dictionary)
• Array initializer
• Expression-bodied methods/properties
• String interpolation: $"{default}"
• Dynamic: F(dynamic d): F(default)

Code

• Statements:
  • if (default) { }
  • switch (default) { }
  • switch (e) { case default: }
  • switch (e1) { case e2 when (default): }
  • while (default) { }, do { } while (default)
  • for (; default; ) { }
  • foreach (... in default) { }
  • throw default;
  • return default;
  • try  { } catch (e) when (default) { }
  • lock (default) { }
  • using (default) { }
  • fixed (byte* p = default) { }
  • yield return default;
  • this = default; in struct .ctor
• Expressions:
  • default.F
  • default()
  • default[i]
  • a[default]
  • nameof(default)
  • checked(default), unchecked(default), checked(default + x)
  • unary: op default
    • !default
  • binary: e op default, default op e
    • default == false
    • new S() == default for struct S with/without operator==, default has type S not S?
    • default + x with user-defined operator or conversion
  • default ? e1 : e2, e1 ? default : e2
  • default ?? e, e ?? default
  • (T)default
  • x op= default
    • x += default with user-defined operator or conversion
  • *default, &default, default->F
  • default is e, e is default
  • await default
  • __refvalue(default, T), _reftype(default), __makeref(default)
• Lambdas: F(Func<T> f), F(Action a): F(() => default)
• Target typing (var, lambdas, integrals)
• Conversions
  • boxing/unboxing
  • DefaultOrNullLiteralConversion
• Nullable (wrapping, unwrapping)
• Anonymous types
• Tuples
• LINQ: select default
• Ref return values
• Overload resolution:
  • F(int i), F(string s): F(default)
  • F(Task<T> t), F(ValueTask<T> t): F(async () => default)
• Type inference
• WRN_IsAlwaysTrue, WRN_IsAlwaysFalse, WRN_AlwaysNull
• __arglist: F(object o, __arglist): F(null, default)

IDE

• Colorization
• Intellisense: default(, default., default[
• Squiggles
• More: Discussion: IDE Test Plan for New Language Features #8389

Debugger / EE

• Compiling expressions in Immediate/Watch windows or hovering over an expression
• Compiling expressions in [DebuggerDisplay("...")]
• Assigning values in Locals/Autos/Watch windows

[cston]

See #18717