swiftlang/swift

[SR-6207] Misleading error for unqualified use of static variable in method

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#48,759 opened on Oct 24, 2017

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 (8 comments) (0 reactions) (0 assignees)Swift (69,989 stars) (10,719 forks)batch import
bugcompilerdiagnostics qualityexpressionsgood first issuestatic declarationsswift 6.0type checker

Description
Previous ID SR-6207
Radar rdar://problem/24291352
Original Reporter @huonw
Type Bug
Status In Progress
Resolution

Swift 4
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, StarterBug
Assignee None
Priority Medium

md5: 47c00d1618aecdca414e977e2fbf19c9

Issue Description:

struct HasStatic {
    func foo() {
        print(cvar)
    }
    static let cvar = 123
}

hasstatic.swift:3:11: error: static member 'cvar' cannot be used on instance of type 'HasStatic'
    print(cvar)
          ^~~~
          HasStatic.

The fixit helps, but it still isn't obvious what's going wrong. The compiler is acting like the use of cvar was written self.cvar, and hints at this with "an instance of", but it's easy to gloss over the subtlety. The text could be tweaked, maybe like

static member 'cvar' can only be used on the type 'HasStatic', not the instance 'X'

where the X is the relevant parent value. (e.g. self for this case, or foo.bar for foo.bar.cvar).

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.
clear
Prerequisites
None
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
The issue is about improving a diagnostic message in the Swift compiler. The error occurs when a static member is used unqualified in an instance context. The diagnostic is emitted by the compiler's semantic analysis (Sema). Look at the file lib/Sema/CSSimplify.cpp or similar files where static member access is resolved. The fix involves changing the error message string to be more explicit, e.g., 'static member 'cvar' can only be used on the type 'HasStatic', not the instance 'X'. Since the issue is labeled StarterBug and is in the swift repository, a good starting point is to search for the exact error message in the codebase and modify it accordingly.
[SR-6207] Misleading error for unqualified use of static variable in method · swiftlang/swift#48759 | Good First Issue