swiftlang/swift

[SR-5337] Improve diagnostic for 'var' in parameter position

Open

#47,911 opened on Jun 29, 2017

View on GitHub
 (2 comments) (0 reactions) (0 assignees)Swift (10,719 forks)batch import
compilerdiagnostics qualitygood first issueimprovement

Repository metrics

Stars
 (69,989 stars)
PR merge metrics
 (Avg merge 8d 17h) (510 merged PRs in 30d)

Description
Previous ID SR-5337
Radar None
Original Reporter @CodaFi
Type Improvement
Votes 1
Component/s Compiler
Labels Improvement, DiagnosticsQoI, StarterBug
Assignee None
Priority Medium

md5: df452a4dc52959caff3a154681f76513

Issue Description:

For code that looks like this

func foo(inout x : Int) {}

or

func foo(_ f : (Int) -> Void) {}

foo { (var x) in
  
}

We used to offer to remove the errant 'var' specifier and extract it into a variable in the body of the function/closure. This diagnostic necessitated a compromise in our modeling of parameter declarations that I have removed. In its place, it would be nice to have a diagnostic of similar quality.

Some ideas would be to redo the old diagnostic, but by first "enqueueing" it then emitting the variable into the body of the function/closure after we parse the opening brace/'in' after a parameter list. Or we could simply do what we do for 'inout' and remove the 'var' specifier then assume the user actually wanted 'inout', etc.

Contributor guide

Research direction
Study the current diagnostic for 'var' in parameter position and reimplement the old fix it by enqueueing a diagnostic and emitting a variable declaration in the body after parsing the opening brace or 'in' keyword.
Tech stack
swift
Domain
compilers
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
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.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Swift
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75