[4.2] Eagerly create init(from:) when looking up 'init' on a Decodable type #17732
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
…swiftlang#17712) Otherwise, the initializer won't be inherited properly onto a subclass, resulting in the base class being allocated instead of the subclass when using Sub.init(from:). https://bugs.swift.org/browse/SR-8083 (cherry picked from commit 9ee996c)
|
@swift-ci Please test |
|
@swift-ci Please nominate |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Explanation: When initializers are inherited onto a subclass, the compiler looks up all initializers on the base class via the name
init. However, this was dodging the implicit synthesis logic for Decodable'sinit(from:), leading to the base class initializer being ignored and then silently inherited as-is onto the subclass (instead of making an override that knows to allocate a different type!). This resulted in a miscompile.Scope: Affects all lookups of
initandencode(without argument names), but only changes behavior if the type in question conforms to Decodable. A compiler performance smoke test showed no significant compile time change.Issue: SR-8083 / rdar://problem/41426211
Risk: Medium-low. This is getting called in a lot more places, but most types don't conform to Decodable, and any that did were already running this code, just a little later.
Testing: Added compiler regression tests.
Reviewed by: @slavapestov, @itaiferber