Add option to not indent conditional compilation blocks

Documentation/Configuration.md

@@ -59,6 +59,10 @@ top-level keys and values:
     If false (the default), arguments will be laid out horizontally first, with
     line breaks only being fired when the line length would be exceeded.
 
+*   `indentConditionalCompilationBlocks` _(boolean)_: Determines if
+    conditional compilation blocks are indented. If this setting is `false` the body
+    of `#if`, `#elseif`, and `#else` is not indented. Defaults to `true`.
+
 > TODO: Add support for enabling/disabling specific syntax transformations in
 > the pipeline.
 

Sources/SwiftFormatConfiguration/Configuration.swift

@@ -29,6 +29,7 @@ public class Configuration: Codable {
     case blankLineBetweenMembers
     case lineBreakBeforeControlFlowKeywords
     case lineBreakBeforeEachArgument
+    case indentConditionalCompilationBlocks
     case rules
   }
 
@@ -87,6 +88,9 @@ public class Configuration: Codable {
   /// each argument, forcing the entire argument list to be laid out vertically.
   public var lineBreakBeforeEachArgument = false
 
+  /// Determines the indentation behavior for `#if`, `#elseif`, and `#else`.
+  public var indentConditionalCompilationBlocks = true
+
   /// Constructs a Configuration with all default values.
   public init() {
     self.version = highestSupportedConfigurationVersion
@@ -129,6 +133,8 @@ public class Configuration: Codable {
       ?? true
     self.lineBreakBeforeEachArgument
       = try container.decodeIfPresent(Bool.self, forKey: .lineBreakBeforeEachArgument) ?? true
+    self.indentConditionalCompilationBlocks
+      = try container.decodeIfPresent(Bool.self, forKey: .indentConditionalCompilationBlocks) ?? true
     self.rules = try container.decodeIfPresent([String: Bool].self, forKey: .rules) ?? [:]
   }
 
@@ -145,6 +151,7 @@ public class Configuration: Codable {
     try container.encode(
       lineBreakBeforeControlFlowKeywords, forKey: .lineBreakBeforeControlFlowKeywords)
     try container.encode(lineBreakBeforeEachArgument, forKey: .lineBreakBeforeEachArgument)
+    try container.encode(indentConditionalCompilationBlocks, forKey: .indentConditionalCompilationBlocks)
     try container.encode(rules, forKey: .rules)
   }
 }

Sources/SwiftFormatPrettyPrint/TokenStreamCreator.swift

@@ -843,16 +843,26 @@ private final class TokenStreamCreator: SyntaxVisitor {
       preconditionFailure()
     }
 
+    let breakKindOpen: BreakKind
+    let breakKindClose: BreakKind
+    if config.indentConditionalCompilationBlocks {
+      breakKindOpen = .open
+      breakKindClose = .close
+    } else {
+      breakKindOpen = .same
+      breakKindClose = .same
+    }
+
     let tokenToOpenWith = node.condition?.lastToken ?? node.poundKeyword
-    after(tokenToOpenWith, tokens: .break(.open), .open)
+    after(tokenToOpenWith, tokens: .break(breakKindOpen), .open)
 
     // Unlike other code blocks, where we may want a single statement to be laid out on the same
     // line as a parent construct, the content of an `#if` block must always be on its own line;
     // the newline token inserted at the end enforces this.
     if let lastElemTok = node.elements.lastToken {
-      after(lastElemTok, tokens: .break(.close), .newline, .close)
+      after(lastElemTok, tokens: .break(breakKindClose), .newline, .close)
     } else {
-      before(tokenToOpenWith.nextToken, tokens: .break(.close), .newline, .close)
+      before(tokenToOpenWith.nextToken, tokens: .break(breakKindClose), .newline, .close)
     }
     return .visitChildren
   }

Tests/SwiftFormatPrettyPrintTests/IfConfigTests.swift

@@ -1,3 +1,5 @@
+import SwiftFormatConfiguration
+
 public class IfConfigTests: PrettyPrintTestCase {
   public func testBasicIfConfig() {
     let input =
@@ -56,6 +58,65 @@ public class IfConfigTests: PrettyPrintTestCase {
     assertPrettyPrintEqual(input: input, expected: expected, linelength: 45)
   }
 
+  public func testIfConfigNoIndentation() {
+    let input =
+      """
+      #if someCondition
+        let a = 123
+        let b = "abc"
+      #endif
+
+      #if someCondition
+        let a = 123
+        let b = "abc"
+      #else
+        let c = 456
+        let d = "def"
+      #endif
+
+      #if swift(>=4.0)
+        print("Stuff")
+      #endif
+      #if swift(>=4.0)
+        print("Stuff")
+      #elseif compiler(>=3.0)
+        print("More Stuff")
+        print("Another Line")
+      #endif
+      """
+
+    let expected =
+      """
+      #if someCondition
+      let a = 123
+      let b = "abc"
+      #endif
+
+      #if someCondition
+      let a = 123
+      let b = "abc"
+      #else
+      let c = 456
+      let d = "def"
+      #endif
+
+      #if swift(>=4.0)
+      print("Stuff")
+      #endif
+      #if swift(>=4.0)
+      print("Stuff")
+      #elseif compiler(>=3.0)
+      print("More Stuff")
+      print("Another Line")
+      #endif
+
+      """
+
+    let config = Configuration()
+    config.indentConditionalCompilationBlocks = false
+    assertPrettyPrintEqual(input: input, expected: expected, linelength: 45, configuration: config)
+  }
+
   public func testPoundIfAroundMembers() {
     let input =
       """