Remove redundant Void from protocol definitions (#1824)

Sources/Rules/RedundantVoidReturnType.swift

@@ -30,8 +30,13 @@ public extension FormatRule {
                 return
             }
 
-            guard formatter.next(.nonSpaceOrCommentOrLinebreak, after: endIndex) == .startOfScope("{")
-            else { return }
+            guard let nextToken = formatter.next(.nonSpaceOrCommentOrLinebreak, after: endIndex) else { return }
+
+            let isInProtocol = nextToken == .endOfScope("}") || (nextToken.isKeywordOrAttribute && nextToken != .keyword("in"))
+
+            // After a `Void` we could see the start of a function's body, or if the function is inside a protocol declaration
+            // we can find a keyword related to other declarations or the end scope of the protocol definition.
+            guard nextToken == .startOfScope("{") || isInProtocol else { return }
 
             guard let prevIndex = formatter.index(of: .endOfScope(")"), before: i),
                   let parenIndex = formatter.index(of: .startOfScope("("), before: prevIndex),
@@ -40,7 +45,14 @@ public extension FormatRule {
             else {
                 return
             }
-            formatter.removeTokens(in: i ..< formatter.index(of: .nonSpace, after: endIndex)!)
+
+            let startRemoveIndex: Int
+            if isInProtocol, formatter.token(at: i - 1)?.isSpace == true {
+                startRemoveIndex = i - 1
+            } else {
+                startRemoveIndex = i
+            }
+            formatter.removeTokens(in: startRemoveIndex ..< formatter.index(of: .nonSpace, after: endIndex)!)
         }
     }
 }

Tests/Rules/BlankLinesBetweenScopesTests.swift

@@ -49,7 +49,7 @@ class BlankLinesBetweenScopesTests: XCTestCase {
     }
 
     func testNoBlankLineBetweenFunctionsInProtocol() {
-        let input = "protocol Foo {\n    func bar() -> Void\n    func baz() -> Int\n}"
+        let input = "protocol Foo {\n    func bar()\n    func baz() -> Int\n}"
         testFormatting(for: input, rule: .blankLinesBetweenScopes)
     }
 

Tests/Rules/RedundantVoidReturnTypeTests.swift

@@ -91,4 +91,25 @@ class RedundantVoidReturnTypeTests: XCTestCase {
         let options = FormatOptions(closureVoidReturn: .preserve)
         testFormatting(for: input, rule: .redundantVoidReturnType, options: options)
     }
+
+    func testRemoveRedundantVoidInProtocolDeclaration() {
+        let input = """
+        protocol Foo {
+            func foo() -> Void
+            func bar() -> ()
+            var baz: Int { get }
+            func bazz() -> ( )
+        }
+        """
+
+        let output = """
+        protocol Foo {
+            func foo()
+            func bar()
+            var baz: Int { get }
+            func bazz()
+        }
+        """
+        testFormatting(for: input, [output], rules: [.void, .redundantVoidReturnType])
+    }
 }