GetSymbolInfo for ValueTuple<int,int> says the type has no locations

[gafter]

When I reference the assembly that defines ValueTuple, and then instantiate it in source, the SemanticModel says that the type has no locations. In particular, it has no locations from metadata, and all (zero of) its locations are from source, so it appears at first glance to be from source.

We should confirm this is the intended behavior.

/cc @dpoeschl @jmarolf @CyrusNajmabadi @VSadov

[dpoeschl]

@gafter On second validation, it looks like there are no locations in this case, which surprises Rename into crashing since it was invoked on a token and it expected that token to be a location of the symbol.

[gafter]

@dpoeschl Why would you expect that to be a location for the symbol? Did the semantic model report that as a declaration point for the type (i.e. GetDeclaredSymbol returning something)?

[dpoeschl]

@gafter No, GetDeclaredSymbol didn't return anything. It shouldn't be a Location of the symbol in this case.

What I meant to say was: For symbols that have no Locations in metadata, it expected the token to be a Location of the symbol returned by GetSymbolInfo when called on that token. This is no longer the case. Maybe it was a faulty assumption all along and there are other examples where this falls down, we've just never hit them...

[jaredpar]

What is the impact of this bug in the current state of the product? Need to understand if it still meets the RTM bar.

[gafter]

This would likely be fixed as a side-effect of the changes proposed for #20648