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proposals/extended-nameof-scope.md

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+# Extended `nameof` scope
+
+## Summary
+
+Allow `nameof(parameter)` inside an attribute on a method or parameter.
+For example:
+- `[MyAttribute(nameof(parameter))] void M(int parameter) { }`
+- `[MyAttribute(nameof(TParameter))] void M<TParameter>() { }`
+- `void M(int parameter, [MyAttribute(nameof(parameter))] int other) { }`
+
+## Motivation
+
+Attributes like `NotNullWhen` or `CallerExpression` need to refer to parameters, but those parameters are currently not in scope.
+
+## Detailed design
+
+[Methods](https://github.com/dotnet/csharplang/blob/master/spec/classes.md#methods)
+
+The method's *type_parameters* are in scope throughout the *method_declaration*, and can be used to form types throughout that scope in *return_type*, *method_body*, and *type_parameter_constraints_clauses* but not in *attributes*, except within a `nameof` expression in *attributes*.
+
+[Method parameters](https://github.com/dotnet/csharplang/blob/master/spec/classes.md#method-parameters)
+
+Names are introduced into this declaration space by the type parameter list and the formal parameter list of the method in `nameof` expressions in attributes placed on the method or its parameters.
+
+Within a `nameof` expression in attributes placed on the method or its parameters, formal parameters can be referenced by their identifiers in *simple_name* expressions.
+
+[Simple names](https://github.com/dotnet/csharplang/blob/master/spec/expressions.md#simple-names)
+
+If `K` is zero and the *simple_name* appears within a `nameof` expression TODO... block and if the block's (or an enclosing block's) local variable declaration space (Declarations) contains a local variable, parameter or constant with name I, then the simple_name refers to that local variable, parameter or constant and is classified as a variable or value.
+
+If `K` is zero and the simple_name appears within the body of a generic method declaration and if that declaration includes a type parameter with name I, then the simple_name refers to that type parameter.
+
+TODO
+
+[Scopes](https://github.com/dotnet/csharplang/blob/master/spec/basic-concepts.md#scopes)
+
+## Related spec sections
+- [Declarations](https://github.com/dotnet/csharplang/blob/master/spec/basic-concepts.md#declarations)