Added blankLinesAroundMark rule

README.md

@@ -271,6 +271,28 @@ Here are all the rules that SwiftFormat currently applies, and the effects that
   var baz: Bool
   var quux: Int
 ```
+
+***blankLinesAroundMark*** - adds a blank line before and after each `MARK:` comment. This rule can be configured using the `--insertlines` option:
+
+```diff
+  func foo() {
+    // foo
+  }
+  // MARK: bar
+  func bar() {
+    // bar
+  }
+
+  func foo() {
+    // foo
+  }
++
+  // MARK: bar
++
+  func bar() {
+    // bar
+  }
+```
                          
 ***braces*** - implements K&R (default) or Allman-style indentation, depending on the `--allman` option:
 

Sources/Rules.swift

@@ -672,6 +672,24 @@ extension FormatRules {
         }
     }
 
+    /// Adds a blank line around MARK: comments
+    @objc public class func blankLinesAroundMark(_ formatter: Formatter) {
+        guard formatter.options.insertBlankLines else { return }
+        formatter.forEachToken { i, token in
+            guard case let .commentBody(comment) = token, comment.hasPrefix("MARK:"),
+                let startIndex = formatter.index(of: .nonSpace, before: i),
+                formatter.tokens[startIndex] == .startOfScope("//") else { return }
+            if let nextIndex = formatter.index(of: .linebreak, after: i),
+                formatter.next(.nonSpace, after: nextIndex)?.isLinebreak == false {
+                formatter.insertToken(.linebreak(formatter.options.linebreak), at: nextIndex)
+            }
+            if let lastIndex = formatter.index(of: .linebreak, before: startIndex),
+                formatter.last(.nonSpace, before: lastIndex)?.isLinebreak == false {
+                formatter.insertToken(.linebreak(formatter.options.linebreak), at: lastIndex)
+            }
+        }
+    }
+
     /// Always end file with a linebreak, to avoid incompatibility with certain unix tools:
     /// http://stackoverflow.com/questions/2287967/why-is-it-recommended-to-have-empty-line-in-the-end-of-file
     @objc public class func linebreakAtEndOfFile(_ formatter: Formatter) {

Tests/RulesTests.swift

@@ -1364,6 +1364,65 @@ class RulesTests: XCTestCase {
         XCTAssertEqual(try format(input + "\n", rules: FormatRules.default, options: options), output + "\n")
     }
 
+    // MARK: blankLinesAroundMark
+
+    func testInsertBlankLinesAroundMark() {
+        let input = """
+        let foo = "foo"
+        // MARK: bar
+        let bar = "bar"
+        """
+        let output = """
+        let foo = "foo"
+
+        // MARK: bar
+
+        let bar = "bar"
+        """
+        XCTAssertEqual(try format(input, rules: [FormatRules.blankLinesAroundMark]), output)
+        XCTAssertEqual(try format(input + "\n", rules: FormatRules.default), output + "\n")
+    }
+
+    func testNoInsertExtraBlankLinesAroundMark() {
+        let input = """
+        let foo = "foo"
+
+        // MARK: bar
+
+        let bar = "bar"
+        """
+        XCTAssertEqual(try format(input, rules: [FormatRules.blankLinesAroundMark]), input)
+        XCTAssertEqual(try format(input + "\n", rules: FormatRules.default), input + "\n")
+    }
+
+    func testInsertBlankLineAfterMarkAtStartOfFile() {
+        let input = """
+        // MARK: bar
+        let bar = "bar"
+        """
+        let output = """
+        // MARK: bar
+
+        let bar = "bar"
+        """
+        XCTAssertEqual(try format(input, rules: [FormatRules.blankLinesAroundMark]), output)
+        XCTAssertEqual(try format(input + "\n", rules: FormatRules.default), output + "\n")
+    }
+
+    func testInsertBlankLineBeforeMarkAtEndOfFile() {
+        let input = """
+        let foo = "foo"
+        // MARK: bar
+        """
+        let output = """
+        let foo = "foo"
+
+        // MARK: bar
+        """
+        XCTAssertEqual(try format(input, rules: [FormatRules.blankLinesAroundMark]), output)
+        XCTAssertEqual(try format(input + "\n", rules: FormatRules.default), output + "\n")
+    }
+
     // MARK: linebreakAtEndOfFile
 
     func testLinebreakAtEndOfFile() {