Fix redundantReturn with consecutive if statements

Sources/FormattingHelpers.swift

@@ -1199,15 +1199,14 @@ extension Formatter {
     /// Finds all of the branch bodies in an if statement.
     /// Returns the index of the `startOfScope` and `endOfScope` of each branch.
     func ifStatementBranches(at ifIndex: Int) -> [ConditionalBranch] {
+        assert(tokens[ifIndex] == .keyword("if"))
         var branches = [(startOfBranch: Int, endOfBranch: Int)]()
         var nextConditionalBranchIndex: Int? = ifIndex
 
         while let conditionalBranchIndex = nextConditionalBranchIndex,
-              ["if", "else"].contains(tokens[conditionalBranchIndex].string),
-              let startOfBody = index(of: .startOfScope, after: conditionalBranchIndex),
-              tokens[startOfBody] == .startOfScope("{"),
-              let endOfBody = endOfScope(at: startOfBody),
-              tokens[endOfBody] == .endOfScope("}")
+              conditionalBranchIndex == ifIndex || tokens[conditionalBranchIndex] == .keyword("else"),
+              let startOfBody = index(of: .startOfScope("{"), after: conditionalBranchIndex),
+              let endOfBody = endOfScope(at: startOfBody)
         {
             branches.append((startOfBranch: startOfBody, endOfBranch: endOfBody))
             nextConditionalBranchIndex = index(of: .nonSpaceOrCommentOrLinebreak, after: endOfBody)
@@ -1219,6 +1218,7 @@ extension Formatter {
     /// Finds all of the branch bodies in a switch statement.
     /// Returns the index of the `startOfScope` and `endOfScope` of each branch.
     func switchStatementBranches(at switchIndex: Int) -> [ConditionalBranch] {
+        assert(tokens[switchIndex] == .keyword("switch"))
         guard let startOfSwitchScope = index(of: .startOfScope("{"), after: switchIndex),
               let firstCaseIndex = index(of: .nonSpaceOrCommentOrLinebreak, after: startOfSwitchScope),
               tokens[firstCaseIndex].isSwitchCaseOrDefault

Tests/RulesTests+Redundancy.swift

@@ -2659,6 +2659,23 @@ class RedundancyTests: RulesTests {
         testFormatting(for: input, output, rule: FormatRules.redundantReturn, options: options)
     }
 
+    func testNoRemoveReturnInConsecutiveIfStatements() {
+        let input = """
+        func foo() -> String? {
+            if bar {
+                return nil
+            }
+            if baz {
+                return "baz"
+            } else {
+                return "quux"
+            }
+        }
+        """
+        let options = FormatOptions(swiftVersion: "5.9")
+        testFormatting(for: input, rule: FormatRules.redundantReturn, options: options)
+    }
+
     func testRedundantIfStatementReturnInRedundantClosure() {
         let input = """
         let value = {