Allow to customize Rule severity

In order to customize the severity of rules, I added
the possibility to do so via the configuration files.
If no severity is specified, we use the one pre-determined
by the Rule itself.

Example:
```
{
    "rules": {
        "AlwaysUseLowerCamelCase": "warning",
        "AmbiguousTrailingClosureOverload": "error",
        "UseLetInEveryBoundCaseVariable": "true", // use rule default
        "UseWhereClausesInForLoops": "false", // disabled
    }
}
```

In addition, one can now control how pretty-print violations
should be treated in the same way

Example:
```
{
    "rules": {
        "TrailingComma": "warning",
        "LineLength": "error",
        "Indentation": "true", // use rule default
        "TrailingWhitespace": "false", // disabled
    }
}
```

Issue: #879

Author: bkolb

.gitignore

@@ -2,4 +2,4 @@
 .swiftpm/
 swift-format.xcodeproj/
 Package.resolved
-
+.index-build

Documentation/RuleDocumentation.md

@@ -4,7 +4,7 @@
 
 Use the rules below in the `rules` block of your `.swift-format`
 configuration file, as described in
-[Configuration](Configuration.md). All of these rules can be
+[Configuration](Documentation/Configuration.md). All of these rules can be
 applied in the linter, but only some of them can format your source code
 automatically.
 

Sources/SwiftFormat/API/Configuration+Default.swift

@@ -22,7 +22,6 @@ extension Configuration {
   /// the JSON will be populated from this default configuration.
   public init() {
     self.rules = Self.defaultRuleEnablements
-    self.ruleSeverity = [:]
     self.maximumBlankLines = 1
     self.lineLength = 100
     self.tabWidth = 8

Sources/SwiftFormat/API/Configuration.swift

@@ -27,6 +27,8 @@ public struct Configuration: Codable, Equatable {
   public enum RuleSeverity: String, Codable, CaseIterable, Equatable, Sendable {
     case warning = "warning"
     case error = "error"
+    case ruleDefault = "true"
+    case disabled = "false"
   }
 
   private enum CodingKeys: CodingKey {
@@ -59,7 +61,7 @@ public struct Configuration: Codable, Equatable {
   /// names.
   ///
   /// This value is generated by `generate-swift-format` based on the `isOptIn` value of each rule.
-  public static let defaultRuleEnablements: [String: Bool] = RuleRegistry.rules
+  public static let defaultRuleEnablements: [String: Configuration.RuleSeverity] = RuleRegistry.rules
 
   /// The version of this configuration.
   private var version: Int = highestSupportedConfigurationVersion
@@ -68,11 +70,7 @@ public struct Configuration: Codable, Equatable {
 
   /// The dictionary containing the rule names that we wish to run on. A rule is not used if it is
   /// marked as `false`, or if it is missing from the dictionary.
-  public var rules: [String: Bool]
-
-  /// The dictionary containing the severities for the rule names that we wish to run on. If a rule
-  /// is not listed here, the default severity is used.
-  public var ruleSeverity: [String: RuleSeverity]
+  public var rules: [String: Configuration.RuleSeverity]
 
   /// The maximum number of consecutive blank lines that may appear in a file.
   public var maximumBlankLines: Int
@@ -398,11 +396,8 @@ public struct Configuration: Codable, Equatable {
     // default-initialized. To get an empty rules dictionary, one can explicitly
     // set the `rules` key to `{}`.
     self.rules =
-      try container.decodeIfPresent([String: Bool].self, forKey: .rules)
+      try container.decodeIfPresent([String: Configuration.RuleSeverity].self, forKey: .rules)
       ?? defaults.rules
-
-    self.ruleSeverity =
-    try container.decodeIfPresent([String: RuleSeverity].self, forKey: .ruleSeverity) ?? [:]
   }
 
   public func encode(to encoder: Encoder) throws {
@@ -499,3 +494,16 @@ public struct NoAssignmentInExpressionsConfiguration: Codable, Equatable {
 
   public init() {}
 }
+
+extension Configuration.RuleSeverity {
+  func findingSeverity(ruleDefault: Finding.Severity) -> Finding.Severity {
+    switch self {
+    case .warning: return .warning
+    case .error: return .error
+    case .ruleDefault:
+      return ruleDefault
+    case .disabled:
+      return .disabled
+    }
+  }
+}

Sources/SwiftFormat/API/Finding.swift

@@ -18,6 +18,7 @@ public struct Finding {
     case error
     case refactoring
     case convention
+    case disabled
   }
 
   /// The file path and location in that file where a finding was encountered.

Sources/SwiftFormat/API/FindingCategorizing.swift

@@ -21,19 +21,8 @@ public protocol FindingCategorizing: CustomStringConvertible {
   ///
   /// By default, all findings are warnings. Individual categories or configuration may choose to override this to
   /// make the findings in those categories more severe.
-  func severity(configuration: Configuration) -> Finding.Severity
+  var severity: Finding.Severity { get }
 
   /// The name of the category.
-  var name: String {get}
-}
-
-extension FindingCategorizing {
-    func severity(configuration: Configuration) -> Finding.Severity {
-        return severityFromConfig(configuration: configuration)
-    }
-
-    func severityFromConfig(configuration: Configuration) -> Finding.Severity {
-        guard let customSeverity = configuration.ruleSeverity[self.name] else { return .warning }
-        return customSeverity.findingSeverity
-    }
+  var name: String { get }
 }

Sources/SwiftFormat/Core/Context.swift

@@ -108,7 +108,12 @@ public final class Context {
     let ruleName = ruleNameCache[ObjectIdentifier(rule)] ?? R.ruleName
     switch ruleMask.ruleState(ruleName, at: loc) {
     case .default:
-      return configuration.rules[ruleName] ?? false
+      guard let configSeverity = configuration.rules[ruleName] else { return false }
+      if case .disabled = configSeverity {
+        return false
+      } else {
+        return true
+      }
     case .disabled:
       return false
     }

Sources/SwiftFormat/Core/FindingEmitter.swift

@@ -55,7 +55,7 @@ final class FindingEmitter {
       Finding(
         category: category,
         message: message,
-        severity: category.severity(configuration: context.configuration),
+        severity: category.severity,
         location: location,
         notes: notes
       )

Sources/SwiftFormat/Core/Rule.swift

@@ -86,7 +86,8 @@ extension Rule {
       syntaxLocation = nil
     }
 
-    let severity: Finding.Severity? = severity ?? context.configuration.findingSeverity(for: type(of: self))
+    let severity: Finding.Severity =
+      severity ?? context.configuration.findingSeverity(for: type(of: self), defaultSeverity: .warning)
 
     let category = RuleBasedFindingCategory(ruleType: type(of: self), severity: severity)
     context.findingEmitter.emit(
@@ -100,8 +101,8 @@ extension Rule {
 }
 
 extension Configuration {
-  func findingSeverity(for rule: any Rule.Type) -> Finding.Severity? {
-    guard let severity = self.ruleSeverity[rule.ruleName] else { return nil }
-    return severity.findingSeverity
+  func findingSeverity(for rule: any Rule.Type, defaultSeverity: Finding.Severity) -> Finding.Severity {
+    guard let severity = self.rules[rule.ruleName] else { return defaultSeverity }
+    return severity.findingSeverity(ruleDefault: defaultSeverity)
   }
 }

Sources/SwiftFormat/Core/RuleBasedFindingCategory.swift

@@ -22,22 +22,15 @@ struct RuleBasedFindingCategory: FindingCategorizing {
 
   var description: String { ruleType.ruleName }
 
-  var severity: Finding.Severity?
+  var severity: Finding.Severity
 
   var name: String {
     return description
   }
 
   /// Creates a finding category that wraps the given rule type.
-  init(ruleType: Rule.Type, severity: Finding.Severity? = nil) {
+  init(ruleType: Rule.Type, severity: Finding.Severity) {
     self.ruleType = ruleType
     self.severity = severity
   }
-
-  func severity(configuration: Configuration) -> Finding.Severity {
-    if let severity = severity {
-        return severity
-    }
-    return severityFromConfig(configuration: configuration)
-  }
 }