Fix redundantStaticSelf false positive inside closures and nested functions (#2518)

Co-authored-by: calda <1811727+calda@users.noreply.github.com>

Sources/FormattingHelpers.swift

@@ -2553,11 +2553,14 @@ extension Formatter {
                      .keyword("func") where lastKeyword != "import":
                     lastKeyword = ""
                     let members = classOrStatic ? classMembers : members
+                    // For the staticSelf (redundantStaticSelf) rule, nested functions are not
+                    // within the static func scope, so Self. should be preserved inside them.
+                    let effectiveClassOrStatic = staticSelf && !isTypeRoot ? false : classOrStatic
                     processFunction(at: &index, localNames: localNames, members: members,
                                     typeStack: &typeStack, closureStack: &closureStack, membersByType: &membersByType,
                                     classMembersByType: &classMembersByType,
                                     usingDynamicLookup: usingDynamicLookup,
-                                    classOrStatic: classOrStatic)
+                                    classOrStatic: effectiveClassOrStatic)
                     classOrStatic = false
                     continue
                 case .keyword("static"):
@@ -2946,10 +2949,12 @@ extension Formatter {
 
                     closureStack.append((allowsImplicitSelf: closureAllowsImplicitSelf(), selfCapture: selfCapture))
                     index = (inIndex ?? index) + 1
+                    // For the staticSelf (redundantStaticSelf) rule, closures are not within
+                    // the static func scope, so Self. should be preserved inside them.
                     processBody(at: &index, localNames: closureLocalNames, members: members,
                                 typeStack: &typeStack, closureStack: &closureStack,
                                 membersByType: &membersByType, classMembersByType: &classMembersByType,
-                                usingDynamicLookup: usingDynamicLookup, classOrStatic: classOrStatic,
+                                usingDynamicLookup: usingDynamicLookup, classOrStatic: staticSelf ? false : classOrStatic,
                                 isTypeRoot: false, isInit: isInit)
                     index -= 1
                     closureStack.removeLast()

Tests/Rules/RedundantStaticSelfTests.swift

@@ -91,16 +91,7 @@ final class RedundantStaticSelfTests: XCTestCase {
             }
         }
         """
-        let output = """
-        enum E {
-            static func foo() {
-                func bar() {
-                    foo()
-                }
-            }
-        }
-        """
-        testFormatting(for: input, output, rule: .redundantStaticSelf)
+        testFormatting(for: input, rule: .redundantStaticSelf)
     }
 
     func testRedundantStaticSelfInNestedType() {
@@ -240,4 +231,37 @@ final class RedundantStaticSelfTests: XCTestCase {
         """
         testFormatting(for: input, rule: .redundantStaticSelf, exclude: [.wrapFunctionBodies])
     }
+
+    func testPreserveStaticSelfInClosureInsideStaticFunc() {
+        let input = """
+        enum XError: Error {
+            case error(String, cause: (any Error)? = nil)
+
+            static func error(_ message: String, cause: String?) -> Self {
+                .error(message, cause: cause.map { Self.error($0) })
+            }
+        }
+        """
+        testFormatting(for: input, rule: .redundantStaticSelf)
+    }
+
+    func testRedundantStaticSelfRemovedOutsideClosureInsideStaticFunc() {
+        let input = """
+        enum E {
+            static func foo() {
+                Self.bar()
+                let x = { Self.bar() }
+            }
+        }
+        """
+        let output = """
+        enum E {
+            static func foo() {
+                bar()
+                let x = { Self.bar() }
+            }
+        }
+        """
+        testFormatting(for: input, output, rule: .redundantStaticSelf)
+    }
 }