swiftlang/swift

[SR-1553] [QOI] Warn on discarded binding of () result

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#44,162 opened on May 18, 2016

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compilerdiagnostics qualitygood first issueimprovement

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Description
Previous ID SR-1553
Radar None
Original Reporter @ddunbar
Type Improvement
Votes 0
Component/s Compiler
Labels Improvement, DiagnosticsQoI
Assignee zsalloum (JIRA)
Priority Medium

md5: a541dcf4281d920a0880df5d3eabc2fa

Issue Description:

Swift should warn on the code below:

$ cat x.swift
func f0() -> () {}
let _ = f0()

$ swiftc -c x.swift
$

This is somewhat related to SE-0047, in that if you use let _ = ... to discard results, and then later refactor the code to not return a result, Swift won't help you find the other places in the code base to update.

Contributor guide

Research direction
Examine the Swift compiler's type checker or Sema to add a diagnostic warning when a binding with `let =` discards a value of type `()`. Look for existing unused result warnings and pattern analysis.
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