_SwiftSyntaxCShims: rename Swift getter

[compnerd]

_errno is a C reserved identifier. Windows uses this reserved namespace and results in a collision. Rename the getter to namespace it and avoid the collision.

[compnerd]

@swift-ci please test

[ahoppen]

Why is _errno a reserved C identifier? As far as I know only identifiers with two underscores and a lowercase letter or a single underscore followed by an uppercase letter are reserved.

Also, if we change this, I think we should also prefix _stdout etc in swiftsyntax_stdio.h for consistency.

[compnerd]

I can change _stdout et al as well.

_ symbols are always reserved: https://en.cppreference.com/w/c/language/identifier

All external identifiers that begin with an underscore.

The same applies to C++. However, C++ additionally reserves any identifier with __ in the name (as opposed to C where it is just a leader).

[compnerd]

@swift-ci please test

[ahoppen]

Hmm, interesting. I didn’t know about the external identifiers rule, assuming that external means external linkage here, the spec doesn’t seem to be clear on that.

But then we shouldn’t prefix the symbol with an underscore at all, ie. change it to swift_syntax_errno instead of _swift_syntax_errno, which is technically still reserved, right?

[compnerd]

Yeah, anything with external linkage (though I think that there would be a conflict since _errno is defined. You should however be able to use it within a function as a variable name.

I can strip the _ on these decls.

[compnerd]

@swift-ci please test

[ahoppen]

@swift-ci Please test

[compnerd]

@swift-ci please test Windows platform