optional_data_string_conversion throws error

[HHuckebein]

New Issue Checklist

• [ x] I've Updated SwiftLint to the latest version.
• [ x] I've searched for existing GitHub issues.

Bug Description

When using the code below, SwiftLint 0.57.0 reports an error like this Optional Data -> String Conversion Violation: Prefer failable String(data:encoding:) initializer when converting Data to String (optional_data_string_conversion)

but following the advice leads to Value of optional type 'String?' must be unwrapped to a value of type 'String'.

// This triggers a violation:
    var description: String {
        do {
            let data = try encode()
            return String(decoding: data, as: UTF8.self)
        } catch {
            return error.message.description
        }
    }

Mention the command or other SwiftLint integration method that caused the issue. Include stack traces or command output.

None

Environment

• SwiftLint version (run swiftlint version to be sure) 0.57.0
• Xcode version (run xcodebuild -version to be sure) Xcode 16.2 Build version 16B5100e
• Installation method used (Homebrew, CocoaPods, building from source, etc) Homebrew
• Configuration file:

disabled_rules:

opt_in_rules:
- collection_alignment
#- conditional_returns_on_newline
- convenience_type
- empty_count
- empty_string
- fallthrough
- fatal_error_message
- file_header
- file_name
- file_name_no_space
- first_where
- flatmap_over_map_reduce
- for_where
- force_unwrapping
- identical_operands
- implicit_return
- implicitly_unwrapped_optional
- is_disjoint
- joined_default_parameter
- legacy_multiple
- legacy_random
- last_where
- lower_acl_than_parent
- modifier_order
- multiline_parameters
- overridden_super_call
- prefixed_toplevel_constant
- prefer_zero_over_explicit_init
- private_action
- private_outlet
- static_operator
- strict_fileprivate
- toggle_bool
#- trailing_closure
- unavailable_function
- unowned_variable_capture
- unneeded_parentheses_in_closure_argument
- untyped_error_in_catch
- yoda_condition

analyzer_rules:
- unused_declaration
- unused_import

excluded: # paths to ignore during linting.
- Frameworks
- Products
- Recovered References
- Carthage
- packages/*/Package.swift
- Packages/*/Package.swift

- packages/*/Tests/
- Packages/*/Tests/

# Default rule configuration
cyclomatic_complexity:
    ignores_case_statements: true

empty_count:
    only_after_dot: true

function_parameter_count: 6

function_body_length: 80

identifier_name:
    allowed_symbols: _ # Is used for private property definitions
    max_length: 50

    excluded:
        - id
        - at
        - on
        - to
        - cc
        - i
        - ok
        - no
        - qa
        - ID
        - xl
        - d1
        - d2
        - tr
        - vc
        - up
        - by

large_tuple: # warn user when using 4 values in tuple, give error if there are 5
- 3

line_length: 200

nesting:
    type_level: 3

type_body_length: 270

type_name:
    max_length: 60
    excluded:
    - AX
    - LS

# Opt-in rule configuration
file_name:
 excluded:
 - "BundleConfig_Root.swift"
 - "BundleConfig_Root+Extension.swift"
 - "BundleConfig_Insurance.swift"
 - "BundleConfig_Insurance+Extension.swift"

file_header:
 required_pattern: |
                    \/\/
                    \/\/ Copyright \(c\) *******\. All rights reserved\.
                    \/\/

Are you using nested configurations? If so, paste their relative paths and respective contents.

[SimplyDanny]

That's the idea of the rule. It asks you to use the failable initializer to make you think about the error case. Your current code will just fail at runtime in case data cannot be converted.

[HHuckebein]

The object created by try encode() is non-optional and String(decoding: data, as: UTF8.self) is a non-failing initializer.

[SimplyDanny]

String(decoding: data, as: UTF8.self)

String(decoding: data, as: UTF8.self) may panic at runtime if data cannot be represented as UTF-8.