Don't hoist visibility for extensions adding protocols

Sources/ParsingHelpers.swift

@@ -1014,6 +1014,17 @@ extension Formatter {
             }
         }
 
+        /// The opening tokens of the declaration (before the body)
+        var openTokens: [Token] {
+            switch self {
+            case .declaration:
+                return []
+            case let .type(_, open, _, _),
+                 let .conditionalCompilation(open, _, _):
+                return open
+            }
+        }
+
         /// The body of this declaration, if applicable
         var body: [Declaration]? {
             switch self {

Sources/Rules.swift

@@ -4973,6 +4973,14 @@ public struct _FormatRules {
             // remove the keyword from the individual declarations and
             // place it on the extension itself.
             case .onExtension:
+                if extensionVisibility == nil,
+                    let delimiterIndex = declaration.openTokens.index(of: .delimiter(":")),
+                    declaration.openTokens.index(of: .keyword("where")).map({ $0 > delimiterIndex }) ?? true
+                {
+                    // Extension adds protocol conformance so can't have visibility modifier
+                    return declaration
+                }
+
                 let visibilityOfBodyDeclarations = formatter
                     .mapDeclarations(body) {
                         formatter.visibility(of: $0) ?? extensionVisibility ?? .internal

Tests/RulesTests+Organization.swift

@@ -1503,4 +1503,27 @@ extension RulesTests {
         """
         testFormatting(for: input, rule: FormatRules.extensionAccessControl)
     }
+
+    func testNoHoistAccessModifierForExtensionThatAddsProtocolConformance() {
+        let input = """
+        extension Foo: Bar {
+            public func bar() {}
+        }
+        """
+        testFormatting(for: input, rule: FormatRules.extensionAccessControl)
+    }
+
+    func testProtocolConformanceCheckNotFooledByWhereClause() {
+        let input = """
+        extension Foo where Self: Bar {
+            public func bar() {}
+        }
+        """
+        let output = """
+        public extension Foo where Self: Bar {
+            func bar() {}
+        }
+        """
+        testFormatting(for: input, output, rule: FormatRules.extensionAccessControl)
+    }
 }

Tests/XCTestManifests.swift

@@ -1077,6 +1077,7 @@ extension RulesTests {
         ("testNoExtraSpaceInsideMultilineHeaderdocCommentType2", testNoExtraSpaceInsideMultilineHeaderdocCommentType2),
         ("testNoExtraSpaceInsideMultilineSwiftPlaygroundDocComment", testNoExtraSpaceInsideMultilineSwiftPlaygroundDocComment),
         ("testNoFractionGrouping", testNoFractionGrouping),
+        ("testNoHoistAccessModifierForExtensionThatAddsProtocolConformance", testNoHoistAccessModifierForExtensionThatAddsProtocolConformance),
         ("testNoHoistAccessModifierForOpenMethod", testNoHoistAccessModifierForOpenMethod),
         ("testNoHoistClosureVariables", testNoHoistClosureVariables),
         ("testNoHoistIfFirstArgSpecified", testNoHoistIfFirstArgSpecified),
@@ -1489,6 +1490,7 @@ extension RulesTests {
         ("testPrivateRequiredStaticFuncModifiers", testPrivateRequiredStaticFuncModifiers),
         ("testPrivateSetModifierNotMangled", testPrivateSetModifierNotMangled),
         ("testPropertyTypeNotConvertedToSugar", testPropertyTypeNotConvertedToSugar),
+        ("testProtocolConformanceCheckNotFooledByWhereClause", testProtocolConformanceCheckNotFooledByWhereClause),
         ("testPublicExtensionMemberACLStripped", testPublicExtensionMemberACLStripped),
         ("testPublicInitCoderUnavailable", testPublicInitCoderUnavailable),
         ("testPublicInitCoderUnavailable2", testPublicInitCoderUnavailable2),