Proposal: dotnet/csharplang#7104
Speclet: https://github.com/dotnet/csharplang/blob/main/proposals/csharp-13.0/lock-object.md
Runtime API proposal: dotnet/runtime#34812

• -langversion check
• lock (expr)
  • calls EnterLockScope
  • finally block calls Scope.Dispose
• Monitor APIs used for converted Lock expression
• warning for conversions
  • implicit/explicit conversion to base class
  • implicit/explicit conversion to derived class (add warning)
  • implicit/explicit conversion to interface
  • implicit/explicit conversion to dynamic
  • explicit conversion to Lock
  • implicit/explicit user-defined conversion (no warning)
  • implicit conversion from as
  • implicit conversion from best common type
• use as argument to parameter of generic type (no warning)
• Obsolete (no diagnostics)
• async
  • with await in lock body
  • with no await in lock body
  • async local function
  • async lambda
• iterators
  • with yield in lock body
  • with no yield in lock body
• async iterator that returns IAsyncEnumerable
• unexpected and missing members
  • Lock defined as struct
  • Lock defined as ref struct
  • Lock defined as interface
  • Scope defined as class
  • Scope defined as struct
  • EnterLockScope missing
  • Scope missing
  • Scope.Dispose missing
  • Lock inaccessible
  • Scope inaccessible
  • EnterLockScope inaccessible
  • Scope.Dispose inaccessible
  • Lock generic
  • Scope generic
  • EnterLockScope generic
  • Scope.Dispose generic
  • Scope not a member of Lock
  • EnterLockScope with parameters
  • EnterLockScope with optional or params parameters
  • EnterLockScope returns void
  • EnterLockScope returns type other than Scope
  • Scope.Dispose with parameters
  • Scope.Dispose with optional or params parameters
  • Scope.Dispose returns type
  • EnterLockScope is static
  • Scope.Dispose is static
  • EnterLockScope overloads
  • Scope.Dispose overloads
  • EnterLockScope defined on base class
  • Scope defined on base class
  • EnterLockScope as virtual, override, hidden
  • Scope.Dispose as virtual, override, hidden
  • EnterLockScope as explicit implementation
  • Scope.Dispose as explicit implementation
  • EnterLockScope use-site errors
  • Scope use-site errors
  • Scope.Dispose use-site errors
• nullable analysis: within lock (expr) { } body, expr is treated as not null (not specific to Lock)
• IOperation
• ControlFlowGraph
  • with Lock members
  • missing Lock members
  • VB: with Lock members
  • VB: missing Lock members
• SemanticModel: confirm SemanticModel does not expose specific locking APIs used
• VB: error for use in SyncLock
• VB: warning for conversions
  • implicit/explicit conversion to base class
  • implicit/explicit conversion to interface
  • explicit conversion to Lock
• add to Compiler Test plan.md
• EnC: verify Dispose() is invoked after editing lock body
• Add VB test with Enter/Exit and Try/Finally when net9 is available. See Handle Lock type in VB #71927 (comment).
• Check what the final API shape is (EnterLockScope name in particular) and rename if necessary.

Productivity

• minbar (done)
• fixer