swiftlang/swift

[SR-11295] There should be a warning for unnecessary casts

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#53,696 opened on Aug 12, 2019

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compilergood first issueimprovement

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Description
Previous ID SR-11295
Radar None
Original Reporter cukier (JIRA User)
Type Improvement
Votes 0
Component/s Compiler
Labels Improvement, StarterBug
Assignee None
Priority Medium

md5: 134fdcf76ae60512bbc5e443ad8390d7

Issue Description:

Swift should warn you if you're performing a cast to a type that the thing is already

        let a = "Hello"
        _ = a as String

I would expect something like "casting expression to `String` doesn't change the type" with a fixit of removing "as String"

Contributor guide

Research direction
Study the Swift type checker to find where cast expressions are evaluated. Add a diagnostic (warning) when the source type is equal to the target type. Provide a fix it to remove the cast.
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.
Half day
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
Swiftcompiler internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65