Split Symbol.swift to reduce complexity of the file

Sources/SymbolKit/Mixin.swift

@@ -0,0 +1,24 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2021 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+import Foundation
+
+/**
+ A protocol that allows extracted symbols to have extra data
+ aside from the base ``SymbolGraph/Symbol``.
+ */
+public protocol Mixin: Codable {
+    /**
+     The key under which a mixin's data is filed.
+
+     > Important: With respect to deserialization, this framework assumes `mixinKey`s between instances of `SymbolMixin` are unique.
+     */
+    static var mixinKey: String { get }
+}

Sources/SymbolKit/SymbolGraph/Misc/LineList.swift → Sources/SymbolKit/SymbolGraph/LineList/LineList.swift

@@ -202,37 +202,3 @@ extension SymbolGraph.LineList {
         }
     }
 }
-
-extension SymbolGraph.LineList {
-    /**
-     Represents a selection in text: a start and end position, a half-open range.
-     */
-    public struct SourceRange: Equatable, Codable {
-        /**
-         The range's start position.
-         */
-        public var start: Position
-
-        /**
-         The range's end position.
-         */
-        public var end: Position
-    }
-}
-
-extension SymbolGraph.LineList.SourceRange {
-    /**
-     Represents a cursor position in text.
-     */
-    public struct Position: Equatable, Codable {
-        /**
-         The zero-based line number of a document.
-         */
-        public var line: Int
-
-        /**
-         The zero-based *byte offset* into a line.
-         */
-        public var character: Int
-    }
-}

Sources/SymbolKit/SymbolGraph/LineList/SourceRange/SourceRange+Position.swift

@@ -0,0 +1,28 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2021 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+import Foundation
+
+extension SymbolGraph.LineList.SourceRange {
+    /**
+     Represents a cursor position in text.
+     */
+    public struct Position: Equatable, Codable {
+        /**
+         The zero-based line number of a document.
+         */
+        public var line: Int
+
+        /**
+         The zero-based *byte offset* into a line.
+         */
+        public var character: Int
+    }
+}

Sources/SymbolKit/SymbolGraph/LineList/SourceRange/SourceRange.swift

@@ -0,0 +1,28 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2021 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+import Foundation
+
+extension SymbolGraph.LineList {
+    /**
+     Represents a selection in text: a start and end position, a half-open range.
+     */
+    public struct SourceRange: Equatable, Codable {
+        /**
+         The range's start position.
+         */
+        public var start: Position
+
+        /**
+         The range's end position.
+         */
+        public var end: Position
+    }
+}