Allow comments in .swift-format (#1014)

* Allow comments in `.swift-format`

Author: antigluten

Sources/SwiftFormat/API/Configuration.swift

@@ -292,7 +292,11 @@ public struct Configuration: Codable, Equatable {
 
   /// Creates a new `Configuration` by decoding it from the UTF-8 representation in the given data.
   public init(data: Data) throws {
-    self = try JSONDecoder().decode(Configuration.self, from: data)
+    let jsonDecoder = JSONDecoder()
+    #if canImport(Darwin) || compiler(>=6)
+    jsonDecoder.allowsJSON5 = true
+    #endif
+    self = try jsonDecoder.decode(Configuration.self, from: data)
   }
 
   public init(from decoder: Decoder) throws {

Tests/SwiftFormatTests/API/ConfigurationTests.swift

@@ -23,6 +23,9 @@ final class ConfigurationTests: XCTestCase {
 
     let emptyDictionaryData = "{}\n".data(using: .utf8)!
     let jsonDecoder = JSONDecoder()
+    #if canImport(Darwin) || compiler(>=6)
+    jsonDecoder.allowsJSON5 = true
+    #endif
     let emptyJSONConfig =
       try! jsonDecoder.decode(Configuration.self, from: emptyDictionaryData)
 
@@ -79,7 +82,11 @@ final class ConfigurationTests: XCTestCase {
         }
         """.data(using: .utf8)!
 
-      let config = try JSONDecoder().decode(Configuration.self, from: jsonData)
+      let jsonDecoder = JSONDecoder()
+      #if canImport(Darwin) || compiler(>=6)
+      jsonDecoder.allowsJSON5 = true
+      #endif
+      let config = try jsonDecoder.decode(Configuration.self, from: jsonData)
       XCTAssertEqual(config.reflowMultilineStringLiterals, expectedBehavior)
     }
   }
@@ -99,9 +106,33 @@ final class ConfigurationTests: XCTestCase {
         }
         """.data(using: .utf8)!
 
-      let config = try JSONDecoder().decode(Configuration.self, from: jsonData)
+      let jsonDecoder = JSONDecoder()
+      #if canImport(Darwin) || compiler(>=6)
+      jsonDecoder.allowsJSON5 = true
+      #endif
+      let config = try jsonDecoder.decode(Configuration.self, from: jsonData)
       XCTAssertEqual(config.reflowMultilineStringLiterals, expectedBehavior)
     }
   }
 
+  func testConfigurationWithComments() throws {
+    #if !canImport(Darwin) && compiler(<6)
+    try XCTSkipIf(true, "JSONDecoder does not support JSON5")
+    #else
+    let expected = Configuration()
+
+    let jsonData = """
+      {
+          // Indicates the configuration schema version.
+          "version": 1,
+      }
+      """.data(using: .utf8)!
+
+    let jsonDecoder = JSONDecoder()
+
+    jsonDecoder.allowsJSON5 = true
+    let config = try jsonDecoder.decode(Configuration.self, from: jsonData)
+    XCTAssertEqual(config, expected)
+    #endif
+  }
 }