Silence superfluous_else rule for availability conditions (#5857)

CHANGELOG.md

@@ -40,6 +40,11 @@
   [SimplyDanny](https://github.com/SimplyDanny)
   [#5787](https://github.com/realm/SwiftLint/issues/5787)
 
+* Silence `superfluous_else` rule on `if` expressions with only a single
+  availability condition.  
+  [SimplyDanny](https://github.com/SimplyDanny)
+  [#5833](https://github.com/realm/SwiftLint/issues/5833)
+
 * Stop triggering the `control_statement` rule on closures being directly
   called as conditions.  
   [SimplyDanny](https://github.com/SimplyDanny)

Source/SwiftLintBuiltInRules/Rules/Style/SuperfluousElseRule.swift

@@ -69,6 +69,13 @@ struct SuperfluousElseRule: OptInRule {
                     }
                 }
                 """),
+            Example("""
+            if #available(iOS 13, *) {
+                return
+            } else {
+                deprecatedFunction()
+            }
+            """),
         ],
         triggeringExamples: [
             Example("""
@@ -324,10 +331,9 @@ private extension SuperfluousElseRule {
 
 private extension IfExprSyntax {
     var superfluousElse: TokenSyntax? {
-        if elseKeyword == nil {
-            return nil
-        }
-        if !lastStatementExitsScope(in: body) {
+        guard elseKeyword != nil,
+              conditions.onlyElement?.condition.is(AvailabilityConditionSyntax.self) != true,
+              lastStatementExitsScope(in: body) else {
             return nil
         }
         if let parent = parent?.as(IfExprSyntax.self) {