First, I will start with a simple feature description. This is not meant to be a specification, just an English-language description of the feature and the intent.

The feature is to add a new well-known attribute to the compiler, System.Runtime.CompilerServices.SkipLocalsInit that causes method bodies nested "inside" the scope of the attribute to elide the ".locals init" CIL directive that causes the CLR to zero-init local variables and space reserved using the "localloc" instruction. "Nested inside the scope of the attribute" is a concept defined as follows:

1. When the attribute is applied to a module, all emitted methods inside that module, including generated methods, will skip local initialization.
2. When the attribute is applied to a type (including interfaces), all methods inside that type, including generated methods, will skip local initialization.
3. When the attribute is applied to a method, the method and all methods generated by the compiler which contain user-influenced code inside that method (e.g., local functions, lambdas, async methods) will skip local initialization.

Given that definition, the test plan follows.

• Specification checked in to csharplang and/or roslyn.
• Trivial case: method with SkipLocalsInit and >0 locals lists locals but no .locals init flag on emit
• Method with SkipLocalsInit and no locals, but stackalloc doesn't have .locals init flag
• SkipLocalsInit attribute can be mixed with other attributes
• Nested functions inside method with SkipLocalsInit inherit setting
  • Lambdas
  • Local functions
  • Async state machines
  • Iterator state machines
  • Local functions + async & iterator
  • Versions of the previous nested inside one-another
  • SkipLocalsInit doesn't apply to constructor of DisplayClass for closures
• SkipLocalsInit on module applies to generated anonymous type
• Other members
  • Attribute on declaration part of partial method, but not implementation part
    • Same with types
  • Properties
  • Indexers
  • Constructors
    • Field initializers that declare locals, e.g. through out var
  • Finalizers
  • Static versions of previous
  • Property-like event handlers
• SkipLocalsInit on type also applies to all previous members and nested functions/generated members
  • Abstract classes/inheritance
  • Also inherited to generated types
  • Nested types
• SkipLocalsInit on modules
  • Applies to nested versions of all previous
  • Works with netmodule emit
  • If assembly references module with attribute, SkipLocalsInit is not automatically applied to other modules
  • Applies to default interface implementations
• What to emit for EnC?
• Scripting??
• Add supporting type Added CompilerServices.SkipLocalsInitAttribute coreclr#20093
• Update Test Plan doc to mention SkipLocalsInit for future testing

Productivity

• The diagnostic for missing unsafe switch should trigger appropriate fixer to fix the project