[SR-10630] JSONDecoder convertToSnakeCase no longer converts dictionary keys

[swift-ci]

Previous ID	SR-10630
Radar	None
Original Reporter	stjernegard (JIRA User)
Type	Bug

Attachment: Download

Environment

Xcode 10.2.1 (10E1001)
Apple Swift version 5.0.1 (swiftlang-1001.0.82.4 clang-1001.0.46.5)
Target: x86_64-apple-darwin18.5.0

Additional Detail from JIRA

Votes	0
Component/s	Foundation
Labels	Bug, Codable
Assignee	bendjones (JIRA)
Priority	Medium

md5: 5efcc4caa9e3495f987fbfb0a346bfdf

relates to:

• SR-7360 keyDecodingStrategy breaks dictionary-keys

Issue Description:

JSONDecoder has regressed between Swift 4.2.4 and Swift 5.0.

Encoding the value ["camelCase": 1] with .convertToSnakeCase would convert the key in Swift 4, but no longer does so in Swift 5.

I can't find anything in the release notes suggesting that this is an expected outcome.

A Swift file showing the issue is attached.

➤ ./swift-4.2.4-RELEASE.xctoolchain/usr/bin/swift ~/test.swift
{"camel_case":1}

➤ ./swift-5.0-RELEASE.xctoolchain/usr/bin/swift ~/test.swift
{"camelCase":1}

[belkadan]

cc bendjones (JIRA User), @millenomi

[swift-ci]

Comment by Ben D. Jones (JIRA)

Thanks @belkadan I'll take a look.

[itaiferber]

This was a purposeful fix for SR-7360 made in PR-16238

[swift-ci]

Comment by Danni Stjernegård (JIRA)

I see that the old behavior was deemed a bug after a long discussion on the forums. Up until then multiple people, including @belkadan and @itaiferber called it correct and expected behavior.

I've spent the entire day fire fighting after this slipped through our testing and am not sure how we should have noticed the change without combing through the forums.

It was never mentioned in the changelog and I'm seeing that the corelibs-foundation team didn't notice either until just 13 days ago.

Changes like this, that not only breaks existing code, but does so in a way that's not possible to detect by the compiler, would be very appreciated if given a mention a bit more noticeably.

Even searching Google for information, I'm finding nothing except for the forum thread where the change was agreed on. Nothing on the official documentation either.