From review: add some comments, rename some methods, and reorganize tests.

Author: DaveEwing

Sources/SwiftFormat/API/Selection.swift

@@ -18,6 +18,7 @@ public enum Selection {
   case infinite
   case ranges([Range<AbsolutePosition>])
 
+  /// Create a selection from an array of utf8 ranges. An empty array means an infinite selection.
   public init(offsetPairs: [Range<Int>]) {
     if offsetPairs.isEmpty {
       self = .infinite

Sources/SwiftFormat/PrettyPrint/PrettyPrint.swift

@@ -68,8 +68,18 @@ public class PrettyPrinter {
   private let maxLineLength: Int
   private var tokens: [Token]
   private var source: String
+
+  /// keep track of where formatting was disabled in the original source
+  ///
+  /// To format a selection, we insert `enableFormatting`/`disableFormatting` tokens into the
+  /// stream when entering/exiting a selection range. Those tokens include utf8 offsets into the
+  /// original source. When enabling formatting, we copy the text between `disabledPosition` and the
+  /// current position to `outputBuffer`. From then on, we continue to format until the next
+  /// `disableFormatting` token.
   private var disabledPosition: AbsolutePosition? = nil
+  /// true if we're currently formatting
   private var writingIsEnabled: Bool { disabledPosition == nil }
+
   private var outputBuffer: String = ""
 
   /// The number of spaces remaining on the current line.

Sources/SwiftFormat/PrettyPrint/TokenStreamCreator.swift

@@ -2735,7 +2735,7 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
     extractLeadingTrivia(token)
     closeScopeTokens.forEach(appendToken)
 
-    generateEnable(
+    generateEnableFormattingIfNecessary(
       token.positionAfterSkippingLeadingTrivia ..< token.endPositionBeforeTrailingTrivia
     )
 
@@ -2744,7 +2744,7 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
       appendToken(.syntax(token.presence == .present ? token.text : ""))
     }
 
-    generateDisable(token.endPositionBeforeTrailingTrivia)
+    generateDisableFormattingIfNecessary(token.endPositionBeforeTrailingTrivia)
 
     appendTrailingTrivia(token)
     appendAfterTokensAndTrailingComments(token)
@@ -2753,15 +2753,15 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
     return .skipChildren
   }
 
-  func generateEnable(_ range: Range<AbsolutePosition>) {
+  private func generateEnableFormattingIfNecessary(_ range: Range<AbsolutePosition>) {
     if case .infinite = selection { return }
     if !isInsideSelection && selection.overlapsOrTouches(range) {
       appendToken(.enableFormatting(range.lowerBound))
       isInsideSelection = true
     }
   }
 
-  func generateDisable(_ position: AbsolutePosition) {
+  private func generateDisableFormattingIfNecessary(_ position: AbsolutePosition) {
     if case .infinite = selection { return }
     if isInsideSelection && !selection.contains(position) {
       appendToken(.disableFormatting(position))
@@ -3270,19 +3270,19 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
       switch piece {
       case .lineComment(let text):
         if index > 0 || isStartOfFile {
-          generateEnable(position ..< position + piece.sourceLength)
+          generateEnableFormattingIfNecessary(position ..< position + piece.sourceLength)
           appendToken(.comment(Comment(kind: .line, text: text), wasEndOfLine: false))
-          generateDisable(position + piece.sourceLength)
+          generateDisableFormattingIfNecessary(position + piece.sourceLength)
           appendNewlines(.soft)
           isStartOfFile = false
         }
         requiresNextNewline = true
 
       case .blockComment(let text):
         if index > 0 || isStartOfFile {
-          generateEnable(position ..< position + piece.sourceLength)
+          generateEnableFormattingIfNecessary(position ..< position + piece.sourceLength)
           appendToken(.comment(Comment(kind: .block, text: text), wasEndOfLine: false))
-          generateDisable(position + piece.sourceLength)
+          generateDisableFormattingIfNecessary(position + piece.sourceLength)
           // There is always a break after the comment to allow a discretionary newline after it.
           var breakSize = 0
           if index + 1 < trivia.endIndex {
@@ -3297,17 +3297,17 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
         requiresNextNewline = false
 
       case .docLineComment(let text):
-        generateEnable(position ..< position + piece.sourceLength)
+        generateEnableFormattingIfNecessary(position ..< position + piece.sourceLength)
         appendToken(.comment(Comment(kind: .docLine, text: text), wasEndOfLine: false))
-        generateDisable(position + piece.sourceLength)
+        generateDisableFormattingIfNecessary(position + piece.sourceLength)
         appendNewlines(.soft)
         isStartOfFile = false
         requiresNextNewline = true
 
       case .docBlockComment(let text):
-        generateEnable(position ..< position + piece.sourceLength)
+        generateEnableFormattingIfNecessary(position ..< position + piece.sourceLength)
         appendToken(.comment(Comment(kind: .docBlock, text: text), wasEndOfLine: false))
-        generateDisable(position + piece.sourceLength)
+        generateDisableFormattingIfNecessary(position + piece.sourceLength)
         appendNewlines(.soft)
         isStartOfFile = false
         requiresNextNewline = false

Tests/SwiftFormatTests/PrettyPrint/AccessorTests.swift

@@ -81,82 +81,6 @@ final class AccessorTests: PrettyPrintTestCase {
     assertPrettyPrintEqual(input: input, expected: expected, linelength: 45)
   }
 
-  func testBasicAccessorsWithSelections() {
-    let input =
-      """
-      ⏩struct MyStruct {
-        var memberValue: Int
-        var someValue: Int { get { return memberValue + 2 } set(newValue) { memberValue = newValue } }
-      }⏪
-      struct MyStruct {
-        var memberValue: Int
-        var someValue: Int { @objc get { return memberValue + 2 } @objc(isEnabled) set(newValue) { memberValue = newValue } }
-      }
-      struct MyStruct {
-        var memberValue: Int
-        var memberValue2: Int
-        var someValue: Int {
-          get {
-            let A = 123
-            return A
-          }
-          set(newValue) {
-            memberValue = newValue && otherValue
-            ⏩memberValue2 = newValue / 2 && andableValue⏪
-          }
-        }
-      }
-      struct MyStruct {
-        var memberValue: Int
-        var SomeValue: Int { return 123 }
-        var AnotherValue: Double {
-          let out = 1.23
-          return out
-        }
-      }
-      """
-
-    let expected =
-      """
-      struct MyStruct {
-        var memberValue: Int
-        var someValue: Int {
-          get { return memberValue + 2 }
-          set(newValue) { memberValue = newValue }
-        }
-      }
-      struct MyStruct {
-        var memberValue: Int
-        var someValue: Int { @objc get { return memberValue + 2 } @objc(isEnabled) set(newValue) { memberValue = newValue } }
-      }
-      struct MyStruct {
-        var memberValue: Int
-        var memberValue2: Int
-        var someValue: Int {
-          get {
-            let A = 123
-            return A
-          }
-          set(newValue) {
-            memberValue = newValue && otherValue
-            memberValue2 =
-              newValue / 2 && andableValue
-          }
-        }
-      }
-      struct MyStruct {
-        var memberValue: Int
-        var SomeValue: Int { return 123 }
-        var AnotherValue: Double {
-          let out = 1.23
-          return out
-        }
-      }
-      """
-
-    assertPrettyPrintEqual(input: input, expected: expected, linelength: 45)
-  }
-
   func testEmptyAccessorList() {
     // The comment inside the struct prevents it from *also* being collapsed onto a single line.
     let input = """

Tests/SwiftFormatTests/PrettyPrint/CommentTests.swift

@@ -274,62 +274,6 @@ final class CommentTests: PrettyPrintTestCase {
     assertPrettyPrintEqual(input: input, expected: expected, linelength: 80)
   }
 
-  func testContainerLineCommentsWithSelection() {
-    let input =
-      """
-      // Array comment
-      let a = [⏩4⏪56, // small comment
-        789]
-
-      // Dictionary comment
-      let b = ["abc": ⏩456, // small comment
-        "def": 789]⏪
-
-      // Trailing comment
-      let c = [123, 456  // small comment
-      ]
-
-      ⏩/* Array comment */
-      let a = [456, /* small comment */
-        789]
-
-       /* Dictionary comment */
-      let b = ["abc": 456,        /* small comment */
-        "def": 789]⏪
-      """
-
-    let expected =
-      """
-      // Array comment
-      let a = [
-        456, // small comment
-        789]
-
-      // Dictionary comment
-      let b = ["abc": 456,  // small comment
-        "def": 789,
-      ]
-
-      // Trailing comment
-      let c = [123, 456  // small comment
-      ]
-
-      /* Array comment */
-      let a = [
-        456, /* small comment */
-        789,
-      ]
-
-      /* Dictionary comment */
-      let b = [
-        "abc": 456, /* small comment */
-        "def": 789,
-      ]
-      """
-
-    assertPrettyPrintEqual(input: input, expected: expected, linelength: 80)
-  }
-
   func testDocumentationBlockComments() {
     let input =
       """