Allow .self in keypaths

Sources/Rules/PreferKeyPath.swift

@@ -57,9 +57,9 @@ public extension FormatRule {
             }
             var replacementTokens: [Token]
             if nextIndex == lastIndex {
-                // TODO: add this when https://bugs.swift.org/browse/SR-12897 is fixed
-                // replacementTokens = tokenize("\\.self")
-                return
+                // https://bugs.swift.org/browse/SR-12897
+                guard formatter.options.swiftVersion >= "5.10" else { return }
+                replacementTokens = tokenize("\\.self")
             } else {
                 let tokens = formatter.tokens[nextIndex + 1 ... lastIndex]
                 guard tokens.allSatisfy({ $0.isSpace || $0.isIdentifier || $0.isOperator(".") }) else {

Tests/Rules/PreferKeyPathTests.swift

@@ -110,4 +110,18 @@ class PreferKeyPathTests: XCTestCase {
         let options = FormatOptions(swiftVersion: "5.2")
         testFormatting(for: input, rule: .preferKeyPath, options: options)
     }
+
+    func testSelfNotConvertedToKeyPathBefore5_10() {
+        // https://bugs.swift.org/browse/SR-12897
+        let input = "let foo = bar.compactMap { $0 }"
+        let options = FormatOptions(swiftVersion: "5.2")
+        testFormatting(for: input, rule: .preferKeyPath, options: options)
+    }
+
+    func testSelfConvertedToKeyPath() {
+        let input = "let foo = bar.compactMap { $0 }"
+        let output = "let foo = bar.compactMap(\\.self)"
+        let options = FormatOptions(swiftVersion: "5.10")
+        testFormatting(for: input, output, rule: .preferKeyPath, options: options)
+    }
 }