Feature branch - https://github.com/dotnet/roslyn/tree/features/CheckedUserDefinedOperators
Specification - https://github.com/dotnet/csharplang/blob/main/proposals/csharp-11.0/checked-user-defined-operators.md
Proposal: dotnet/csharplang#4665

Compiler

• LangVer
• sync with F# team
• Confirm VB behavior (operators are ignored)
• Confirm C++/CLI does not crash
• Build VS

Compiler Public APIs

• SyntaxNormalizer
• ClassifyConversion
  • Specified position is a checked context
  • No position specified (should we have an overload for specified whether to treat the conversion as checked?)
• SymbolDisplay

Syntax

• checked on
  • concrete conversion operators
  • abstract conversion operators
    • Definitions
    • Explicit implementations
  • implicit conversion operators (error)
  • explicit conversion operators
  • concrete unary operators
  • abstract unary operators
  • concrete binary operators
  • abstract binary operators
• Misplaced checked
• checked in cref
• graceful recovery on unchecked (issue)

Semantics

• checked expression context calls operator
  • Regular operators
  • Compound assignment operators
• checked method context calls operator
  • Regular operators
  • Compound assignment operators
• -checked compiler switch calls operator
  • Regular operators
  • Compound assignment operators
• Source requires matching unchecked operator
• Paired operators in metadata can differ by everything but parameter/return type
• In unchecked contexts, checked operators are ignored during lookup
  • Binary operators
  • Unary operators
  • Conversion operators
• In checked contexts, unchecked operators (regular operators that have a paired checked operator) are ignored during lookup
  • Binary operators
  • Unary operators
  • Conversion operators
• In checked contexts, regular operators that are not unchecked are included during lookup
  • Binary operators
  • Unary operators
  • Conversion operators
• Lifted conversion chooses checked conversions in checked contexts
• DLR behavior
• Expression trees contain new operator types
  • Binary operators
  • Unary operators
  • Conversion operators
• Obsolete
  • Binary operators
  • Unary operators
  • Conversion operators

Productivity

• Declaring checked operators
• Using operators in expressions
• QuickInfo should show whether a checked or regular operator is used
  • User-defined operators
  • Intrinsic operators
• checked keyword classification
• Syntax normalizer for declarations
• checked keyword completion Adjust CheckedKeywordRecommender for checked user-defined operators. #60183
• Go to definition from operator usage and explicit interface implementation
• Find all references for checked operators - doesn't work Find All References doesn't find usages of checked user-defined operators #60216
• Go To Implementation
• Operator completion for explicit implementation - doesn't work Completion list for explicit interface implementation doesn't include checked keyword for checked user-defined operators #60215
• Implement interface fixer - doesn't work Implement interface fixer doesn't spit out checked keyword for checked user-defined operators #60214
• F1 on checked keyword on the declaration goes to the doc page for checked keyword.
• Formatter tests Add formatter and smart indentation tests for checked operators #60375
  • Signature formatting
  • Indentation inside operator
• Navbar - add more miscellaneous tests for checked operators #60727
• Object Browser - add more miscellaneous tests for checked operators #60727
• Metadata as source - add more miscellaneous tests for checked operators #60727

Docs

• We might need to adjust F1 behavior on checked keyword in declarations, depending on structure of the docs. Right now it goes to a general checked keyword topic.