User Defined Compound Assignment Test Plan

Championed proposal: dotnet/csharplang#9101
Speclet: https://github.com/dotnet/csharplang/blob/main/proposals/csharp-14.0/user-defined-compound-assignment.md
Feature branch: https://github.com/dotnet/roslyn/tree/features/UserDefinedCompoundAssignment

• language version
• ref safety analysis
• public API review
  • SyntaxFacts.IsOverloadableCompoundAssignmentOperator(SyntaxKind)
  • IOperation
  • CFG (CompoundAssignment_12, IncrementOrDecrementFlow_03)
  • GetOperatorKind (CompoundAssignment_01480_GetOperatorKind)
  • GetSymbolInfo on the operator
• VB Interop (Tests: CompoundAssignment_01380_VisualBasic, CompoundAssignment_01390_VisualBasic, CompoundAssignment_01400_VisualBasic_Checked, CompoundAssignment_01410_VisualBasic, CompoundAssignment_01420_VisualBasic_Checked)
• Partners
  • F# heads up
  • C++ heads up
  • Docs team heads up
• Obsolete is reported (Increment_087_Consumption_Obsolete, CompoundAssignment_00870_Consumption_Obsolete)
• Accessibility
  • Operator non-public (CompoundAssignment_00022_MustBePublic_ExplicitAccessibility, CompoundAssignment_01440_MetadataValidation, Increment_002_MustBePublic_ExplicitAccessibility, Increment_144_MetadataValidation)
  • Operator public (CompoundAssignment_00010, CompoundAssignment_00021_ImplicitlyPublicInInterface, Increment_001)
• Modifiers
  • New allowed - new/override/readonly (Increment_0XX_AllowedInY, CompoundAssignment_0XX_AllowedInY`)
  • Disallowed - (Increment_0XX_NotAllowedInY, CompoundAssignment_0XX_NotAllowedInY`)
• Must return void (Increment_003_MustReturnVoid, Increment_004_MustReturnVoid_Checked, CompoundAssignment_00030_MustReturnVoid, CompoundAssignment_00040_MustReturnVoid_Checked)
• Operator in interface
  • static - compound assignment disallowed (CompoundAssignment_00013_Not_Static)
  • instance abstract (Increment_009_AbstractAllowedInClassAndInterface, CompoundAssignment_00090_AbstractAllowedInClassAndInterface)
  • instance concrete (Increment_001, CompoundAssignment_00010)
• operator in class/struct
  • static abstract not allowed increment/decrement (Increment_018_AbstractNotAllowedInClass_OnStatic, Increment_019_AbstractNotAllowedInStruct)
  • instance implementation from interface (Increment_012_AbstractCanBeImplementedExplicitlyInClassAndStruct, Increment_013_AbstractCanBeImplementedImplicitlyInClassAndStruct, CompoundAssignment_00120_AbstractCanBeImplementedExplicitlyInClassAndStruct, CompoundAssignment_00130_AbstractCanBeImplementedImplicitlyInClassAndStruct)
• parameter ref kinds (CompoundAssignment_01431_MetadataValidation)
• parameter defaults disallowed (CompoundAssignment_00900_Consumption_BadOperator, CompoundAssignment_00910_Consumption_BadOperator)
• use in expression trees (Increment_145_ExpressionTree, CompoundAssignment_01490_ExpressionTree)
• partial definition/implementation (Increment_146_Partial, CompoundAssignment_01500_Partial, CompoundAssignmentDeclaration_19_Partial, CompoundAssignmentDeclaration_20_Partial, IncrementDeclaration_01_Partial, IncrementDeclaration_02_Partial)
• instance overridding/hiding
  • Overridding (Increment_033_OverrideAllowedInClass, CompoundAssignment_00330_OverrideAllowedInClass, CompoundAssignment_00331_OverrideAllowedInClass)
    • Testing copying modopts from overridden operator (Increment_147_CopyModifiers, CompoundAssignment_01510_CopyModifiers, CompoundAssignment_01520_CopyModifiers)
  • Hiding with/without new (warnings) (Increment_054_NewAllowedInInterface_WRN_NewRequired, Increment_055_NewAllowedInClass_WRN_NewRequired, CompoundAssignment_00540_NewAllowedInInterface_WRN_NewRequired, CompoundAssignment_00550_NewAllowedInClass_WRN_NewRequired)
  • Nullable mismatch on override (CompoundAssignment_01530_NullableMismatchOnOverride)
• Nullability mismatch on operands (Increment_089_Consumption_NullableAnalysis, CompoundAssignment_00890_Consumption_NullableAnalysis, CompoundAssignment_00891_Consumption_NullableAnalysis, Increment_089_Consumption_NullableAnalysis)
• Test instance operator in catch filter (Increment_148_Consumption_InCatchFilter, CompoundAssignment_01540_Consumption_InCatchFilter)
• Operator methods attributed with Unmanaged callers only (CompoundAssignment_00880_Consumption_UnmanagedCallersOnly, Increment_088_Consumption_UnmanagedCallersOnly)
• Use in DebuggerDisplay
• Consumption
  • Both instance and static present for increment (Increment_093_Consumption_RegularVsOperator, CompoundAssignment_00930_Consumption_RegularVsOperator)
  • Checked vs nonchecked (CompoundAssignment_00800_Consumption_CheckedVersionInRegularContext, Increment_080_Consumption_CheckedVersionInRegularContext)
  • Reference safety (CompoundAssignment_00740_Consumption_RefSafety through CompoundAssignment_00753_Consumption_RefSafety)
  • Bad operator detection (CompoundAssignment_00900_Consumption_BadOperator through CompoundAssignment_00912_Consumption_BadOperator, Increment_090_Consumption_BadOperator, Increment_091_Consumption_BadOperator)
  • Operator implementation (CompoundAssignment_01030_Consumption_Implementation, Increment_103_Consumption_Implementation)
  • Operator overriding (CompoundAssignment_01040_Consumption_Overriding, Increment_104_Consumption_Overriding)
  • Shadowing (CompoundAssignment_00810_Consumption_Shadowing through CompoundAssignment_00830_Consumption_Shadowing, Increment_081_Consumption_Shadowing through Increment_083_Consumption_Shadowing)
  • Ambiguity (CompoundAssignment_00850_Consumption_Ambiguity, Increment_085_Consumption_Ambiguity)
  • Interpolated string handler (CompoundAssignment_01470_InterpolatedStringHandlerArgument)
  • Overload resolution priority (CompoundAssignment_01450_Consumption_OverloadResolutionPriority, CompoundAssignment_01460_Consumption_OverloadResolutionPriority_CheckedContext)
  • Interactions with the new c?.Value += blah feature (*_Consumption_ConditionalAccessTarget)

Issue to reserve new operator names - dotnet/runtime#114930

Issues from IDE test pass:

• Unexpected/misleading IDE diagnostics for a user defined assignment operator declaration
• Unexpected/misleading IDE diagnostics for a user defined assignment operator usage
• Implement interface generator adds static modifier for assignment operators
• Implement abstract class fixer adds static and doesn't add override modifier for an assignment operator
• Override completion doesn't offer to override assignment operators
• Go-to-def and Find-refs