only rule should work for individual custom rules

[mildm8nnered]

Addresses #6029 and #6058

Allows individual custom rules to be specified in the only_rules configuration, or the --only-rule command line option, without also having to specify custom_rules.

I think this may bring individual custom_rules to be almost equivalent to "normal" rules, as they are now supported in swiftlint:disable commands, and most other cases as well.

The key change here is that when we calculate the resulting rules, if CustomRules is not in there, we manually add it in.

if !resultingRules.contains(where: { $0 is CustomRules }),
   !customRulesIdentifiers.isDisjoint(with: onlyRulesRuleIdentifiers),
   let customRules {
    resultingRules.append(customRules)
}

There was already pre-existing code later on to filter which custom rules are enabled.

Some further changes were required to make sure that the warning about configured but not enabled rules was fired for this configuration in the only_rules case.

Other changes

We were calling (allRulesWrapped.first { $0.rule is CustomRules })?.rule as? CustomRules in about five different places, so I added a convenience var to [ConfigurationRuleWrapper].

validRuleIdentifiers is now calculated lazily.

Order of custom_rules violations

The order of violations reported by custom_rules was not deterministic - see #6058 - violations are now reported sorted by the custom rule identifier.

There is still some weirdness in the order that violations are output in, but I'll raise those issues elsewhere - they should at least be deterministic now.

[SwiftLintBot]

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[Copilot]

Pull Request Overview

This PR addresses issues #6029 and #6058 by allowing individual custom rules to be enabled via the only_rules configuration (or the --only-rule command line option) without requiring a separate custom_rules configuration. It also adds a convenience property for retrieving CustomRules, sorts custom rule violations deterministically, and updates tests/documentation accordingly.

• Enables specifying individual custom rules in only_rules.
• Introduces lazy evaluation of valid rule identifiers and a new extension for accessing CustomRules.
• Ensures deterministic ordering of custom rule violations.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Tests/FrameworkTests/CustomRulesTests.swift	Adds tests for only_rules support with custom rules enabling
Tests/FrameworkTests/ConfigurationTests.swift	Adds test verifying specific custom rules behavior in the configuration
Source/SwiftLintFramework/Rules/CustomRules.swift	Sorts customRuleConfigurations to guarantee deterministic violation order
Source/SwiftLintFramework/Configuration/Configuration+RulesWrapper.swift	Refactors rule identifier handling and customRules appending logic
Source/SwiftLintFramework/Configuration/Configuration+RulesMode.swift	Updates CustomRules handling in rules mode configurations
Source/SwiftLintFramework/Configuration/Configuration+Parsing.swift	Updates parsing and validation to support custom rule identifiers
CHANGELOG.md	Documents the bug fix and behavior change for custom_rules configuration

[mildm8nnered]

I had these as lazy initially, which should be safe, as resultingRules is locked, and the only other place they are called from is when we're merging configurations, but making them non-lazy seemed safer.