Enable CI format check

.github/workflows/pull_request.yml

@@ -5,9 +5,23 @@ on:
     types: [opened, reopened, synchronize]
 
 jobs:
+  validate_format_config:
+    name: Validate Format Config
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+      - name: Install apt dependencies
+        run: sudo apt-get -qq update && sudo apt-get -qq -y install curl
+      - name: Compare against swift-mmio swift-format config
+        run: |
+          curl -sL https://raw.githubusercontent.com/apple/swift-mmio/refs/heads/main/.swift-format -o .swift-format-mmio
+          diff .swift-format .swift-format-mmio
+
   tests:
     name: Test
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
+
   soundness:
     name: Soundness
     uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
@@ -16,5 +30,3 @@ jobs:
       license_header_check_enabled: false
       # https://github.com/apple/swift-algorithms/issues/251
       docs_check_enabled: false
-      # https://github.com/apple/swift-algorithms/issues/252
-      format_check_enabled: false

.swift-format

@@ -0,0 +1,71 @@
+{
+  "fileScopedDeclarationPrivacy" : {
+    "accessLevel" : "private"
+  },
+  "indentation" : {
+    "spaces" : 2
+  },
+  "indentConditionalCompilationBlocks" : false,
+  "indentSwitchCaseLabels" : false,
+  "lineBreakAroundMultilineExpressionChainComponents" : false,
+  "lineBreakBeforeControlFlowKeywords" : false,
+  "lineBreakBeforeEachArgument" : false,
+  "lineBreakBeforeEachGenericRequirement" : false,
+  "lineLength" : 80,
+  "maximumBlankLines" : 1,
+  "multiElementCollectionTrailingCommas" : true,
+  "noAssignmentInExpressions" : {
+    "allowedFunctions" : [
+      "XCTAssertNoThrow"
+    ]
+  },
+  "prioritizeKeepingFunctionOutputTogether" : false,
+  "respectsExistingLineBreaks" : true,
+  "rules" : {
+    "AllPublicDeclarationsHaveDocumentation" : false,
+    "AlwaysUseLiteralForEmptyCollectionInit" : true,
+    "AlwaysUseLowerCamelCase" : true,
+    "AmbiguousTrailingClosureOverload" : false,
+    "BeginDocumentationCommentWithOneLineSummary" : true,
+    "DoNotUseSemicolons" : true,
+    "DontRepeatTypeInStaticProperties" : true,
+    "FileScopedDeclarationPrivacy" : true,
+    "FullyIndirectEnum" : true,
+    "GroupNumericLiterals" : true,
+    "IdentifiersMustBeASCII" : true,
+    "NeverForceUnwrap" : true,
+    "NeverUseForceTry" : true,
+    "NeverUseImplicitlyUnwrappedOptionals" : true,
+    "NoAccessLevelOnExtensionDeclaration" : true,
+    "NoAssignmentInExpressions" : true,
+    "NoBlockComments" : true,
+    "NoCasesWithOnlyFallthrough" : true,
+    "NoEmptyTrailingClosureParentheses" : true,
+    "NoLabelsInCasePatterns" : true,
+    "NoLeadingUnderscores" : false,
+    "NoParensAroundConditions" : true,
+    "NoPlaygroundLiterals" : true,
+    "NoVoidReturnOnFunctionSignature" : true,
+    "OmitExplicitReturns" : true,
+    "OneCasePerLine" : true,
+    "OneVariableDeclarationPerLine" : true,
+    "OnlyOneTrailingClosureArgument" : true,
+    "OrderedImports" : true,
+    "ReplaceForEachWithForLoop" : true,
+    "ReturnVoidInsteadOfEmptyTuple" : true,
+    "TypeNamesShouldBeCapitalized" : true,
+    "UseEarlyExits" : false,
+    "UseExplicitNilCheckInConditions" : true,
+    "UseLetInEveryBoundCaseVariable" : true,
+    "UseShorthandTypeNames" : true,
+    "UseSingleLinePropertyGetter" : true,
+    "UseSynthesizedInitializer" : true,
+    "UseTripleSlashForDocumentationComments" : true,
+    "UseWhereClausesInForLoops" : false,
+    "ValidateDocumentationComments" : true
+  },
+  "spacesBeforeEndOfLineComments": 2,
+  "spacesAroundRangeFormationOperators" : false,
+  "tabWidth" : 2,
+  "version" : 1
+}

Package.swift

@@ -13,23 +13,23 @@
 import PackageDescription
 
 let package = Package(
-    name: "swift-algorithms",
-    products: [
-        .library(
-            name: "Algorithms",
-            targets: ["Algorithms"]),
-    ],
-    dependencies: [
-        .package(url: "https://github.com/apple/swift-numerics.git", from: "1.0.0"),
-    ],
-    targets: [
-        .target(
-            name: "Algorithms",
-            dependencies: [
-              .product(name: "RealModule", package: "swift-numerics"),
-            ]),
-        .testTarget(
-            name: "SwiftAlgorithmsTests",
-            dependencies: ["Algorithms"]),
-    ]
+  name: "swift-algorithms",
+  products: [
+    .library(
+      name: "Algorithms",
+      targets: ["Algorithms"])
+  ],
+  dependencies: [
+    .package(url: "https://github.com/apple/swift-numerics.git", from: "1.0.0")
+  ],
+  targets: [
+    .target(
+      name: "Algorithms",
+      dependencies: [
+        .product(name: "RealModule", package: "swift-numerics")
+      ]),
+    .testTarget(
+      name: "SwiftAlgorithmsTests",
+      dependencies: ["Algorithms"]),
+  ]
 )

Sources/Algorithms/AdjacentPairs.swift

@@ -126,7 +126,7 @@ extension AdjacentPairsSequence: Sequence {
 }
 
 extension AdjacentPairsSequence: LazySequenceProtocol
-  where Base: LazySequenceProtocol {}
+where Base: LazySequenceProtocol {}
 
 /// A collection of adjacent pairs of elements built from an underlying
 /// collection.
@@ -143,7 +143,8 @@ public struct AdjacentPairsCollection<Base: Collection> {
   @inlinable
   internal init(base: Base) {
     self.base = base
-    self.secondBaseIndex = base.isEmpty
+    self.secondBaseIndex =
+      base.isEmpty
       ? base.endIndex
       : base.index(after: base.startIndex)
   }
@@ -154,7 +155,7 @@ extension AdjacentPairsCollection {
   public struct Index: Comparable {
     @usableFromInline
     internal var first: Base.Index
-    
+
     @usableFromInline
     internal var second: Base.Index
 
@@ -168,7 +169,7 @@ extension AdjacentPairsCollection {
     public static func == (lhs: Index, rhs: Index) -> Bool {
       lhs.first == rhs.first
     }
-    
+
     @inlinable
     public static func < (lhs: Index, rhs: Index) -> Bool {
       lhs.first < rhs.first
@@ -183,7 +184,7 @@ extension AdjacentPairsCollection: Collection {
       first: secondBaseIndex == base.endIndex ? base.endIndex : base.startIndex,
       second: secondBaseIndex)
   }
-  
+
   @inlinable
   public var endIndex: Index {
     Index(first: base.endIndex, second: base.endIndex)
@@ -207,20 +208,23 @@ extension AdjacentPairsCollection: Collection {
   public func index(_ i: Index, offsetBy distance: Int) -> Index {
     guard distance != 0 else { return i }
 
-    guard let result = distance > 0
-      ? offsetForward(i, by: distance, limitedBy: endIndex)
-      : offsetBackward(i, by: -distance, limitedBy: startIndex)
+    guard
+      let result = distance > 0
+        ? offsetForward(i, by: distance, limitedBy: endIndex)
+        : offsetBackward(i, by: -distance, limitedBy: startIndex)
     else { fatalError("Index out of bounds") }
     return result
   }
 
   @inlinable
   public func index(
-    _ i: Index, offsetBy distance: Int, limitedBy limit: Index
+    _ i: Index,
+    offsetBy distance: Int,
+    limitedBy limit: Index
   ) -> Index? {
     guard distance != 0 else { return i }
     guard limit != i else { return nil }
-    
+
     if distance > 0 {
       let limit = limit > i ? limit : endIndex
       return offsetForward(i, by: distance, limitedBy: limit)
@@ -229,38 +233,48 @@ extension AdjacentPairsCollection: Collection {
       return offsetBackward(i, by: -distance, limitedBy: limit)
     }
   }
-  
+
   @inlinable
   internal func offsetForward(
-    _ i: Index, by distance: Int, limitedBy limit: Index
+    _ i: Index,
+    by distance: Int,
+    limitedBy limit: Index
   ) -> Index? {
     assert(distance > 0)
     assert(limit > i)
-
-    guard let newFirst = base.index(i.second, offsetBy: distance - 1, limitedBy: limit.first),
-          newFirst != base.endIndex
+
+    let newFirst = base.index(
+      i.second,
+      offsetBy: distance - 1,
+      limitedBy: limit.first)
+    guard let newFirst, newFirst != base.endIndex
     else { return nil }
+
     let newSecond = base.index(after: newFirst)
-    
+
     precondition(newSecond <= base.endIndex, "Can't advance beyond endIndex")
     return newSecond == base.endIndex
       ? endIndex
       : Index(first: newFirst, second: newSecond)
   }
-  
+
   @inlinable
   internal func offsetBackward(
-    _ i: Index, by distance: Int, limitedBy limit: Index
+    _ i: Index,
+    by distance: Int,
+    limitedBy limit: Index
   ) -> Index? {
     assert(distance > 0)
     assert(limit < i)
-        
+
     let offset = i == endIndex ? 0 : 1
-    guard let newSecond = base.index(
+    let newSecond = base.index(
       i.first,
       offsetBy: -(distance - offset),
       limitedBy: limit.second)
+    guard let newSecond
     else { return nil }
+
     let newFirst = base.index(newSecond, offsetBy: -1)
     precondition(newFirst >= base.startIndex, "Can't move before startIndex")
     return Index(first: newFirst, second: newSecond)
@@ -282,12 +296,12 @@ extension AdjacentPairsCollection: Collection {
 }
 
 extension AdjacentPairsCollection: BidirectionalCollection
-  where Base: BidirectionalCollection
-{
+where Base: BidirectionalCollection {
   @inlinable
   public func index(before i: Index) -> Index {
     precondition(i != startIndex, "Can't offset before startIndex")
-    let second = i == endIndex
+    let second =
+      i == endIndex
       ? base.index(before: base.endIndex)
       : i.first
     let first = base.index(before: second)
@@ -296,10 +310,10 @@ extension AdjacentPairsCollection: BidirectionalCollection
 }
 
 extension AdjacentPairsCollection: RandomAccessCollection
-  where Base: RandomAccessCollection {}
+where Base: RandomAccessCollection {}
 
 extension AdjacentPairsCollection: LazySequenceProtocol, LazyCollectionProtocol
-  where Base: LazySequenceProtocol {}
+where Base: LazySequenceProtocol {}
 
 extension AdjacentPairsCollection.Index: Hashable where Base.Index: Hashable {
   @inlinable