swiftlang/swift

Diagnostic for use of plain protocol name in type position should suggest `some` or `any`

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#68,284 opened on Sep 1, 2023

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bugcompilerdiagnostics qualityexistentialsfix-itsgenericsgood first issueopaque typesswift 5.9type checkertypes

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Description

The following code is invalid:

protocol P {
  associatedtype A
}

func generic(value: P) {}

The compiler currently produces the error message Use of protocol 'P' as a type must be written 'any P' with a fix-it to insert the any keyword.

However, a different (and often better!) fix here is to use the some keyword. The error message should be re-worded to prompt the programmer to consider any or some, and there should be two notes, each with a fix-it to insert any or some, respectively.

Contributor guide

Research direction
Investigate the Swift compiler's diagnostic generation for protocol usage in type positions. Look for the error message 'Use of protocol ... as a type must be written ...' and determine how to add an additional note suggesting 'some'.
Tech stack
swift
Domain
developer experience
Issue type
Feature
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.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
SwiftGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70