[SR-12102] Discrepancy in indexstore for function parameter references

[kastiglione]

Previous ID	SR-12102
Radar	rdar://problem/58999116
Original Reporter	@kastiglione
Type	Bug
Status	Resolved
Resolution	Invalid

Additional Detail from JIRA

Votes	0
Component/s
Labels	Bug
Assignee	None
Priority	Medium

md5: 73c21047efd85ce0ba0a16efe385a836

relates to:

• SR-12096 Index missing references to initializers in Result extensions

Issue Description:

With Swift 5.1, I've noticed that the parameter references in the indexstore vary by how a parameter is labeled.

Consider these three mostly equivalent functions:

func named(n: Int) {
    print(n)
}

func labeled(number n: Int) {
    print(n)
}

func unlabeled(_ n: Int) {
    print(n)
}

In the first case – named(n:), where the parameter n has the default self-named label, the indexstore does (correctly?) contain references to the use of parameter n. Specifically, the print(n) statement has the following references:

  /*
        | function.accessorGetter=getter:n
        | parameter=n */
  print(n)

There's a symbol occurrence named getter:n and it has kind = INDEXSTORE_SYMBOL_KIND_FUNCTION and subkind = INDEXSTORE_SYMBOL_SUBKIND_ACCESSORGETTER.

There's also a symbol occurrence named n and it has kind = INDEXSTORE_SYMBOL_KIND_PARAMETER.

However, in the other two cases – labeled(number:) and unlabeled(_:), there is no symbol occurrences at all for the parameter n. It seems by giving the parameter a custom label, or giving it no label, the index references aren't being generated.

[beccadax]

@swift-ci create

[nathawes]

This is actually intentional behavior. The index normally only records information on non-local symbols in order to keep its size down. In order to support the global rename refactoring though, we make an exception for parameters whose name within the function body is directly tied its external argument label in the containing function.

If I wanted to rename named(n:) to other(m:) in your first example I need to update every occurrence of n within the function body to m. If I wanted to rename labeled(number:) to labeled2(letter:) in your second example I don't need to change the body at all, so we don't record the parameter occurrences in that case. Same for the third example.

Hope that makes sense!

[kastiglione]

Thanks Nathan. Makes sense. Unfortunate, for the use case we had in mind.