Add prefersKeyPath support for contains(where:)

Author: nicklockwood

Sources/Rules.swift

@@ -5118,17 +5118,27 @@ public struct _FormatRules {
     ) { formatter in
         formatter.forEach(.startOfScope("{")) { i, _ in
             guard formatter.options.swiftVersion >= "5.2",
-                  let prevIndex = formatter.index(of: .nonSpaceOrLinebreak, before: i)
+                  var prevIndex = formatter.index(of: .nonSpaceOrLinebreak, before: i)
             else {
                 return
             }
             var prevToken = formatter.tokens[prevIndex]
+            var label: String?
+            if prevToken == .delimiter(":"),
+               let labelIndex = formatter.index(of: .nonSpace, before: prevIndex),
+               case let .identifier(name) = formatter.tokens[labelIndex],
+               let prevIndex2 = formatter.index(of: .nonSpaceOrLinebreak, before: labelIndex)
+            {
+                label = name
+                prevToken = formatter.tokens[prevIndex2]
+                prevIndex = prevIndex2
+            }
             let parenthesized = prevToken == .startOfScope("(")
             if parenthesized {
                 prevToken = formatter.last(.nonSpaceOrLinebreak, before: prevIndex) ?? prevToken
             }
             guard case let .identifier(name) = prevToken,
-                  ["map", "flatMap", "compactMap", "allSatisfy", "filter"].contains(name),
+                  ["map", "flatMap", "compactMap", "allSatisfy", "filter", "contains"].contains(name),
                   let nextIndex = formatter.index(of: .nonSpaceOrLinebreak, after: i, if: {
                       $0 == .identifier("$0")
                   }),
@@ -5137,6 +5147,13 @@ public struct _FormatRules {
             else {
                 return
             }
+            if name == "contains" {
+                if label != "where" {
+                    return
+                }
+            } else if label != nil {
+                return
+            }
             var replacementTokens: [Token]
             if nextIndex == lastIndex {
                 // TODO: add this when https://bugs.swift.org/browse/SR-12897 is fixed
@@ -5149,6 +5166,9 @@ public struct _FormatRules {
                 }
                 replacementTokens = [.operator("\\", .prefix)] + tokens
             }
+            if let label = label {
+                replacementTokens = [.identifier(label), .delimiter(":"), .space(" ")] + replacementTokens
+            }
             if !parenthesized {
                 replacementTokens = [.startOfScope("(")] + replacementTokens + [.endOfScope(")")]
             }

Tests/RulesTests+Syntax.swift

@@ -1893,4 +1893,17 @@ extension RulesTests {
         let options = FormatOptions(swiftVersion: "5.2")
         testFormatting(for: input, rule: FormatRules.preferKeyPath, options: options)
     }
+
+    func testNoMapPropertyToKeyPathForTrailingContains() {
+        let input = "let foo = bar.contains { $0.foo }"
+        let options = FormatOptions(swiftVersion: "5.2")
+        testFormatting(for: input, rule: FormatRules.preferKeyPath, options: options)
+    }
+
+    func testMapPropertyToKeyPathForContainsWhere() {
+        let input = "let foo = bar.contains(where: { $0.foo })"
+        let output = "let foo = bar.contains(where: \\.foo)"
+        let options = FormatOptions(swiftVersion: "5.2")
+        testFormatting(for: input, output, rule: FormatRules.preferKeyPath, options: options)
+    }
 }

Tests/XCTestManifests.swift

@@ -1056,6 +1056,7 @@ extension RulesTests {
         ("testMalformedFunctionNotMisidentifiedAsClosure", testMalformedFunctionNotMisidentifiedAsClosure),
         ("testMapNestedPropertyWithSpacesToKeyPath", testMapNestedPropertyWithSpacesToKeyPath),
         ("testMapPropertyToKeyPath", testMapPropertyToKeyPath),
+        ("testMapPropertyToKeyPathForContainsWhere", testMapPropertyToKeyPathForContainsWhere),
         ("testMarkExtensionsDisabled", testMarkExtensionsDisabled),
         ("testMarkExtensionsIfNotEmpty", testMarkExtensionsIfNotEmpty),
         ("testMarkInsideMultilineComment", testMarkInsideMultilineComment),
@@ -1251,6 +1252,7 @@ extension RulesTests {
         ("testNoMapPropertyToKeyPathForFunctionCalls", testNoMapPropertyToKeyPathForFunctionCalls),
         ("testNoMapPropertyToKeyPathForOptionalChaining", testNoMapPropertyToKeyPathForOptionalChaining),
         ("testNoMapPropertyToKeyPathForSwiftLessThan5_2", testNoMapPropertyToKeyPathForSwiftLessThan5_2),
+        ("testNoMapPropertyToKeyPathForTrailingContains", testNoMapPropertyToKeyPathForTrailingContains),
         ("testNoMapSelfToKeyPath", testNoMapSelfToKeyPath),
         ("testNoMarkFunctionArgument", testNoMarkFunctionArgument),
         ("testNoMarkNamedFunctionArgument", testNoMarkNamedFunctionArgument),