SR-9454: StringProtocol.lineRange(for:) returns invalid range on Linux

[norio-nomura]

Fixes SR-9454

[spevans]

@swift-ci test

[norio-nomura]

We may also need to examine other places that use String.Index.init(encodedOffset:). 🤔

[norio-nomura]

I filed a separate issue about encodedOffset: https://bugs.swift.org/browse/SR-9749

[milseman]

@spevans this change looks good to me and is an important fix for Swift 5. But, I'm not familiar with corelibs-foundation, what do you think?

[spevans]

I think this needs an extra test on a SubString to check that the _substringOffset can be removed as the comment for it is:

  // passing _ns to the Foundation APIs. Will be 0 if self is String.

[norio-nomura]

I believe that this PR will be replaced by the forthcoming PR for swift-corelibs-foundation paired with apple/swift#22108.

[spevans]

This looks fine but if it is to be superseded by a new PR it would be good to keep the test case.

[milseman]

That PR gives new API that you can use instead of having to advance the index yourself. Basically, it will let you simplify your one line of code, but it could be held up for a while awaiting core-team feedback and maybe even some SE work. This change is good and important no matter what happens with that PR, are you ok to merge it @spevans?

[spevans]

Yup, thanks for the explanation, lets get this fix in.

[spevans]

@swift-ci test and merge

[norio-nomura]

Thanks!