[Error]Swift/StringCharacterView.swift:158 Fatal error: String index is out of bounds

[KyosukeKotani]

[Error]Swift/StringCharacterView.swift:158 Fatal error: String index is out of bounds

[hoangatuan]

@rakaramos @ZevEisenberg
I've raised a PR to fix this issue here: #270
Please help to review it when you have time 🙏

[ZevEisenberg]

Hi @KyosukeKotani, and thanks for taking the time to write in! Would you be able to provide a sample project that reproduces the issue?

[KyosukeKotani]

@ZevEisenberg
Thank you for your reply.
I am unable to provide the code where the error occurred immediately as it is a product code.
I will try to reproduce this issue in a sample project.
Please wait a few days.

[KyosukeKotani]

@ZevEisenberg
Thank you for your patience.
We are unable to provide a sample project, but we have identified the cause of the error and provide a sample file.

Sample File

//
//  sample_mutation.swift
//  sample-project
//

import Foundation

public final class SampleError: NSObject, NSCoding {
    public func encode(with coder: NSCoder) {
        <#code#>
    }
    
    public init?(coder: NSCoder) {
        <#code#>
    }
    public let text: String
    
    public let viewCount: Int
    public let activationFlag: Bool
    
    
    public init?(dictionary: [String: Any]) {
        guard
            let text = dictionary["Text"] as? String,
            let activationFlag = dictionary["ActivationFlag"] as? Bool,
            let viewCount = dictionary["ViewCounts"] as? Int,
            !text.isEmpty else {
            return nil
        }
        
        self.text = text
        self.viewCount = viewCount
        self.activationFlag = activationFlag
    }
    
    public func isDiscarded() -> Bool {
        
        if viewCount > 0 {
            return true
        }
        
        return false
    }

    public func isEnabledToShow() -> Bool {
        // バルーンの表示判定
        return activationFlag && !isDiscarded()
    }
}

Error Cause

// バルーンの表示判定

I have confirmed that deleting the above comment will prevent the error from occurring.

[ZevEisenberg]

Just to clarify - is the original comment in Japanese? If you replace the comment with English, does that fix the error? I'm wondering if this is a problem with how we are parsing multi-byte characters.

[KyosukeKotani]

Yes, it is. The original comment is in Japanese.
Replacing the Japanese with English fixes the error.
I too have a feeling that there is a problem with how we are parsing multi-byte characters.

[hoangatuan]

The problem lies at the line 74.
The nodePosition here is UTF-8 offset, but later we treat it as character offset at line 77.
If we use alphabet character, utf-8 offset will equal to character offset since we only need 1 byte for alphabet character.
For non-alphabet character, it uses multi-byte => utf-8 offset is not equal to character offset => Crash