swiftlang/swift

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

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#44,162 建立於 2016年5月18日

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compilerdiagnostics qualitygood first issueimprovement

描述
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.

貢獻者指南

技術棧
swift
領域
developer experiencetooling
議題類型
feature
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
3
預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。
1-2 days
活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。
stale
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
clear
前置要求
basic understanding of Swift compilerfamiliarity with diagnostic emission
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
55
研究方向
Examine the Swift compiler's handling of `let =` bindings, particularly in the type checker's treatment of discardable results. Look at files like `lib/Sema/TypeCheckStmt.cpp` for where `let` patterns are processed and where warnings about unused results are emitted. Consider adding a new diagnostic when the type of the expression is `()`. The existing behavior for ` =` might already warn; check if `let =` is treated differently. Review the discussion in SE 0047 for context.