swiftlang/swift

[SR-4464] Assigning a property to itself fails in 3.1

Open

#47,041 opened on Apr 1, 2017

View on GitHub
 (4 comments) (0 reactions) (0 assignees)Swift (69,989 stars) (10,719 forks)batch import
bugcompilerdiagnostics qualitygood first issue

Description
Previous ID SR-4464
Radar None
Original Reporter @iby
Type Bug
Status In Progress
Resolution

Attachment: Download
Votes 0
Component/s Compiler
Labels Bug, 3.1Regression, DiagnosticsQoI, StarterBug
Assignee None
Priority Medium

md5: 702671bd69d19bebf1a102eb3ec92355

Issue Description:

Prior 3.1 we could assign property to itself if needed with self.name = (self.name), now it fails. Also, see this for details – http://stackoverflow.com/a/31931318/458356.

Just discovered by luck, apparently the supported syntax now is (self.name = self.name), is this official?

Contributor guide

Tech stack
swift
Domain
tooling
Issue type
bug
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.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Swift basicsCompiler toolchain setup
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Review the linked Stack Overflow discussion and the Swift compiler's parser for self assignment syntax. Look at the AST for property access expressions and assignment nodes. The issue may be in how parentheses are handled around the assignment. Check the git history for changes around Swift 3.1 release.