• Speclet checked in to csharplang. (https://github.com/dotnet/csharplang/blob/master/proposals/target-typed-new.md)
• Re-confirm with LDM (done 3/25/2020)

Compiler (general test plan for reference):

• LangVersion (TestInLocal_LangVersion8
• arglist (ArgList, covers new(__arglist) and variants)
• target-typing a nullable type (TestNullableType01, TestNullableType02)
• as default parameter value (TestInParameterDefaultValue), in params (ArrayTypeInferredFromParams)
• in attribute argument (InAttributeParameter)
• struct with a 1-constructor, but no 0-constructor
• in string interpolation (InStringInterpolation)
• in await (TestInAwait, no target-type)
• with explicit cast (TestBadTargetType_Cast)
• is it possible to have a constant value? (TestInParameterDefaultValue, not a constant)
• returning in lambda (with single or multiple returns, TestBestType_Lambda), in async lambda (TestInAsyncLambda_01)
• with unary operators (+new(), ...), equality (1 == new()), compound (x += new()), ternary (x ? y : new() and vice-versa)
• in using (InUsing01), in nameof() (InNameOf), in typeof() (InTypeOf), in sizeof() (InSizeOf), in foreach (InForeach), in deconstruction (TestDeconstruction, var (x, y) = new();), in switch (InSwitch1), in patterns (InIsOperator), in if (ConditionalOnNew), in while (ConditionalOnNew), in fixed (InFixed), as an expression-statement (TestInStatement, new();), in lock (InLock)
• invoking a dynamic method (InvocationOnDynamic, no target-type)
• as initial value for an auto-property (TestInClassInitializer)
• returning in async method (ReturningFromAsyncMethod)
• returning from IEnumerable-returning method
• yielding from iterator method (YieldReturn)
• assign to var (TestTargetType_Var), to nullable type (TestNullableType1),
• semantic model (TestAssignmentToClass, TestAssignmentToStruct, TODO currently shows a natural type)
• type parameter with and without new() and struct constraint (TestTypeParameter, TestTypeParameter_ErrorCases)
• IOperation
• new() { 42 } (TestObjectAndCollectionInitializer)
• test with collection initializer (TestObjectAndCollectionInitializer, new() { 1, 2, 3 })
• in object initializer (new C() { x = new() }), collection initializer (new C() { new D(1), new D(2), new() }) (TestObjectAndCollectionInitializer)
• test with enum type (TestTargetType_Enum), array type, pointer type (TestTargetType_Pointer, error), test in anonymous type (TestTargetType_AnonymousType, error), tuple (TestTargetType_TupleType, okay)
• ref local
• ref return (RefReturnValue1, RefReturnValue2)
• in implicitly-typed array (ImplicitlyTypedArray, no target-type)
• use as L-value (TestAssignment, new() = 1;)
• update the compiler test plan
  -[ ] test interaction with any C# 8.0 feature that was merged earlier: ??= (TestInNullCoalescingAssignment), async-streams, nullability, Ranges (InRange)

IDE:

• formatting
  • no space in new() (SpacingInTargetTypedNew)
  • auto-formatting when typing (string a, string b)[] ab = new (string a, string b)[1]; vs. C c = new();
• verify that completion isn't annoying
• QuickInfo should show the type on new
• UpgradeProject (typically just works)
• colorization
• SignatureHelp should work (it should help tying object creation arguments)
• Is the type of new() visible by hovering, when debugging?
• GoToDefinition on new() should go to the proper constructor
• test existing fixers UseImplicitType and UseExplicitType (for example, List<string> list = new(); should never offer to make the declaration var)
• ExplicitType and target-typed new #42554 (ExplicitType and target-typed new)
• FindAllReferences and target-typed new #42555 (FindAllReferences and target-typed new, PR Bring back naive implementation of FAR for target-typed new #43645)
• Symbol completion and target-typed new #42556 (Symbol completion and target-typed new)
• ChangeSignature and target-typed new #42558 (ChangeSignature and target-typed new)
• AddParameter and target-typed new #42559 (AddParameter and target-typed new)

Open LDM questions:

• Confirm behavior for new[] (Championed: Target-typed implicit array creation expression new[]  csharplang#2701 (comment))

Initial PR: #25196
Proposal: https://github.com/dotnet/csharplang/blob/master/proposals/target-typed-new.md
Championed issue (with LDM history): dotnet/csharplang#100

Relates to #37821 (spec issues with target-typing)