Periphery doesn't account for various uses of properties

[rgoldberg]

Describe the bug

Periphery doesn't account for various uses of properties.

Reproduction

1: When a property is used as a key for a Dictionary:

import Foundation

struct Thing {
	let path: String
}

let thing = Thing(path: "/dev/null")

var thingByPath = [String:Thing]()
thingByPath[thing.path] = thing

for path in thingByPath.keys {
	do {
		try FileManager.default.attributesOfItem(atPath: path)
		print(1)
	} catch {
		print(2)
	}
}

2: When a property is indirectly used like in an implicit use in String(describing:), either directly or via a call to print(_:separator:terminator:):

struct Thing {
	let id: Int
	let name: String
}

print(Thing(id: 1, name: "a"))

Environment

$ periphery version
3.2.0

$ swift -version
swift-driver version: 1.127.14.1 Apple Swift version 6.2.1 (swiftlang-6.2.1.4.8 clang-1700.4.4.1)
Target: arm64-apple-macosx26.0

$ xcodebuild -version
Xcode 26.1.1
Build version 17B100

[ileitch]

1. Is a known bug: False positive with dictionary key #412
2. This works for me, it correctly reports that both id and name and assigned, but unused. Can you please provide a demo project that reproduces the issue you are seeing?

[rgoldberg]

Thanks for the info.

In the second case, the properties will be used because print() causes String(describing:) to be called, which uses the values of the properties to generate a String that is printed.

[ileitch]

Hmm, this is an interesting edge case. Both scenarios are correct, depending on what you want. I'm going to mark this as feature request, as I think we'd need a new option like --retain-struct-properties-via-synthesized-description (but more succinct).

[rgoldberg]

How about --retain-synthesized-uses?

Shorter, plus it covers all synthesized uses, whatever they might be.

[ileitch]

This issue has been migrated to periphery-pro/issues#20 and is now tracked there.

Periphery is moving to a commercial model, and issues are now handled in that repository. You can read about what's changing, and what it means for existing users, in A New Chapter.