Remove BlankLineBetweenMembers rule because it creates non-idempotent behavior.

The rule is unfortunately based on the trivia before the pretty printing pass, which means it decides single-line-ness based on the input which may be incorrect. The single-line-ness must be based on the source *after* pretty printing, so it cannot be accomplished in a phase 1 rule.

Even linting in a phase 1 rule is too inaccurate, because it may flag false positives and false negatives creating useless noise.

In the future, the blank line between members requirement can be better implemented using breaks in the pretty printer.

Author: dylansturg

Documentation/Configuration.md

@@ -38,14 +38,6 @@ top-level keys and values:
     line breaks where absolutely necessary and removing any others, effectively
     canonicalizing the output.
 
-*   `blankLineBetweenMembers` _(object)_: Controls logic specific to the
-    enforcement of blank lines between type members. The object value of this
-    property has the following properties:
-
-    *   `ignoreSingleLineProperties` _(boolean)_: If `true`, then single-line
-        property declarations are allowed to appear consecutively without a
-        blank line separating them.
-
 *   `lineBreakBeforeControlFlowKeywords` _(boolean)_: Determines the
     line-breaking behavior for control flow keywords that follow a closing
     brace, like `else` and `catch`. If true, a line break will be added before
@@ -103,9 +95,6 @@ An example `.swift-format` configuration file is shown below.
     },
     "maximumBlankLines": 1,
     "respectsExistingLineBreaks": true,
-    "blankLineBetweenMembers": {
-        "ignoreSingleLineProperties": true
-    },
     "lineBreakBeforeControlFlowKeywords": true,
     "lineBreakBeforeEachArgument": true
 }

Documentation/IgnoringSource.md

@@ -44,12 +44,12 @@ set of rules, add a comment of the form:
 `// swift-format-ignore: [comma delimited list of rule names]`.
 
 ```swift
-// swift-format-ignore: BlankLineBetweenMembers
+// swift-format-ignore: DoNotUseSemicolons
 struct Foo {
 	   var bar = true
 }
 
-// swift-format-ignore: BlankLineBetweenMembers, FullyIndirectEnum, UseEarlyExits
+// swift-format-ignore: DoNotUseSemicolons, FullyIndirectEnum, UseEarlyExits
 func foo() {
 	    var bar = true
 }

Sources/SwiftFormat/Pipelines+Generated.swift

@@ -13,8 +13,8 @@
 // This file is automatically generated with generate-pipeline. Do Not Edit!
 
 import SwiftFormatCore
-import SwiftSyntax
 import SwiftFormatRules
+import SwiftSyntax
 
 /// A syntax visitor that delegates to individual rules for linting.
 ///
@@ -167,7 +167,6 @@ class LintPipeline: SyntaxVisitor {
 
   override func visit(_ node: MemberDeclBlockSyntax) -> SyntaxVisitorContinueKind {
     visitIfEnabled(AmbiguousTrailingClosureOverload.visit, in: context, for: node)
-    visitIfEnabled(BlankLineBetweenMembers.visit, in: context, for: node)
     return .visitChildren
   }
 
@@ -286,7 +285,6 @@ extension FormatPipeline {
 
   func visit(_ node: Syntax) -> Syntax {
     var node = node
-    node = BlankLineBetweenMembers(context: context).visit(node)
     node = DoNotUseSemicolons(context: context).visit(node)
     node = FullyIndirectEnum(context: context).visit(node)
     node = GroupNumericLiterals(context: context).visit(node)

Sources/SwiftFormatConfiguration/Configuration.swift

@@ -26,7 +26,6 @@ public struct Configuration: Codable, Equatable {
     case tabWidth
     case indentation
     case respectsExistingLineBreaks
-    case blankLineBetweenMembers
     case lineBreakBeforeControlFlowKeywords
     case lineBreakBeforeEachArgument
     case lineBreakBeforeEachGenericRequirement
@@ -72,9 +71,6 @@ public struct Configuration: Codable, Equatable {
 
   /// MARK: Rule-specific configuration
 
-  /// Rules for limiting blank lines between members.
-  public var blankLineBetweenMembers = BlankLineBetweenMembersConfiguration()
-
   /// Determines the line-breaking behavior for control flow keywords that follow a closing brace,
   /// like `else` and `catch`.
   ///
@@ -152,9 +148,6 @@ public struct Configuration: Codable, Equatable {
       = try container.decodeIfPresent(Indent.self, forKey: .indentation) ?? .spaces(2)
     self.respectsExistingLineBreaks
       = try container.decodeIfPresent(Bool.self, forKey: .respectsExistingLineBreaks) ?? true
-    self.blankLineBetweenMembers = try container.decodeIfPresent(
-      BlankLineBetweenMembersConfiguration.self, forKey: .blankLineBetweenMembers)
-      ?? BlankLineBetweenMembersConfiguration()
     self.lineBreakBeforeControlFlowKeywords
       = try container.decodeIfPresent(Bool.self, forKey: .lineBreakBeforeControlFlowKeywords) ?? false
     self.lineBreakBeforeEachArgument
@@ -186,7 +179,6 @@ public struct Configuration: Codable, Equatable {
     try container.encode(tabWidth, forKey: .tabWidth)
     try container.encode(indentation, forKey: .indentation)
     try container.encode(respectsExistingLineBreaks, forKey: .respectsExistingLineBreaks)
-    try container.encode(blankLineBetweenMembers, forKey: .blankLineBetweenMembers)
     try container.encode(lineBreakBeforeControlFlowKeywords, forKey: .lineBreakBeforeControlFlowKeywords)
     try container.encode(lineBreakBeforeEachArgument, forKey: .lineBreakBeforeEachArgument)
     try container.encode(lineBreakBeforeEachGenericRequirement, forKey: .lineBreakBeforeEachGenericRequirement)
@@ -199,16 +191,6 @@ public struct Configuration: Codable, Equatable {
   }
 }
 
-/// Configuration for the BlankLineBetweenMembers rule.
-public struct BlankLineBetweenMembersConfiguration: Codable, Equatable {
-  /// If true, blank lines are not required between single-line properties.
-  public let ignoreSingleLineProperties: Bool
-
-  public init(ignoreSingleLineProperties: Bool = true) {
-    self.ignoreSingleLineProperties = ignoreSingleLineProperties
-  }
-}
-
 /// Configuration for the NoPlaygroundLiterals rule.
 public struct NoPlaygroundLiteralsConfiguration: Codable, Equatable {
   public enum ResolveBehavior: String, Codable {

Sources/SwiftFormatConfiguration/RuleRegistry+Generated.swift

@@ -18,7 +18,6 @@ enum RuleRegistry {
     "AlwaysUseLowerCamelCase": true,
     "AmbiguousTrailingClosureOverload": true,
     "BeginDocumentationCommentWithOneLineSummary": true,
-    "BlankLineBetweenMembers": true,
     "DoNotUseSemicolons": true,
     "DontRepeatTypeInStaticProperties": true,
     "FullyIndirectEnum": true,