swiftlang/swift

[SR-9040] Suggestion when overriding implictly unwrapped optional does not suggest making parameter implictly unwrapped

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#51,543 opened on Oct 18, 2018

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Description
Previous ID SR-9040
Radar None
Original Reporter @JosephDuffy
Type Bug

Apple Swift version 4.2 (swiftlang-1000.11.37.1 clang-1000.11.45.1)
Target: x86_64-apple-darwin18.0.0
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, StarterBug
Assignee None
Priority Medium

md5: 9b7c61d5cf17e72eb3e9d8e02cd54d9f

Issue Description:

When overriding a function that has an implicitly unwrapped optional parameter with a non-optional parameter, the fixit suggests adding ?, making the parameter optional.

I would expect this to offer adding !, along with ?, but I am not sure if this is classed as a bug, or an intentional change due to SE-0054.

Example code that produces the fixit:

class Foo {
    func bar(_ bar: String!) {}
}

class FooSubclass: Foo {
    override func bar(_ bar: String) {}
}

This produces the message: Cannot override instance method parameter of type 'String?' with non-optional type 'String', with an Insert '?' fix.

If this is classed as a bug I'd love to attempt to fix it![]( (if it's not, sorry))

Contributor guide

Tech stack
swift
Domain
developer experiencetooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Swift languagecompiler internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Investigate the Swift compiler's source code in the type checker, particularly the logic that produces fix it suggestions for override mismatches. Look for the function that checks parameter types and generates the 'Insert ?' fix it, and determine how to add a similar fix it for implicitly unwrapped optionals. Test with the provided example code to ensure the new suggestion appears correctly.
[SR-9040] Suggestion when overriding implictly unwrapped optional does not suggest making parameter implictly unwrapped · swiftlang/swift#51543 | Good First Issue