Call to local function inside generic function fails

[ozguronsoy]

Description of the bug:

A call to a local function defined inside a generic function fails with a compiler error.

What did you do, or what's a simple way to reproduce the bug?

fn F(unused T:! type) {
  fn Local() {}
  Local();
}

What did you expect to happen?

This should compile successfully.

What actually happened?

The compiler cannot deduce the generic parameters of the enclosing function while deducing parameters of the local function.

  // CHECK:STDERR: demo.carbon:[[@LINE+7]]:3: error: cannot deduce value for generic parameter `T` [DeductionIncomplete]
  // CHECK:STDERR:   Local();
  // CHECK:STDERR:   ^~~~~~~
  // CHECK:STDERR: demo.carbon:[[@LINE-4]]:3: note: while deducing parameters of generic declared here [DeductionGenericHere]
  // CHECK:STDERR:   fn Local() {}
  // CHECK:STDERR:   ^~~~~~~~~~~~
  // CHECK:STDERR:

Any other information, logs, or outputs that you want to share?

No response

[zygoloid]

It looks like the problem here is that ScopeStack::PushForFunctionBody pushes a scope with a specific of SpecificId::None, which is wrong -- it should be pushing the self specific of the function, so that we treat Local as referring to the function within F(T), not as a generic function with an unbound and deduced T:! type parameter.