From 5e0e7f5f7d6f4d6c4bffcda6a509f48aa2effcda Mon Sep 17 00:00:00 2001
From: Jonathan Flat <jflat@apple.com>
Date: Thu, 3 Jul 2025 13:52:55 -0600
Subject: [PATCH] (154976578) String.pathExtension should allow "..name" file
 names but not ".."

---
 .../String/String+Path.swift                    | 17 +++++++++++------
 .../FoundationEssentialsTests/StringTests.swift | 13 +++++++++++++
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/Sources/FoundationEssentials/String/String+Path.swift b/Sources/FoundationEssentials/String/String+Path.swift
index 975d3f51b..bc149baac 100644
--- a/Sources/FoundationEssentials/String/String+Path.swift
+++ b/Sources/FoundationEssentials/String/String+Path.swift
@@ -224,14 +224,19 @@ extension String {
     }
 
     internal var pathExtension: String {
-        let lastComponent = lastPathComponent.utf8
-        guard lastComponent.last != ._dot,
-              !lastComponent.starts(with: [._dot, ._dot]),
-              let lastDot = lastComponent.lastIndex(of: ._dot),
-              lastDot != lastComponent.startIndex else {
+        let utf8Component = lastPathComponent.utf8
+        guard utf8Component.last != ._dot,
+              let lastDot = utf8Component.lastIndex(of: ._dot),
+              // Don't treat a hidden file name as an extension
+              lastDot != utf8Component.startIndex else {
             return ""
         }
-        let result = String(lastPathComponent[lastComponent.index(after: lastDot)...])
+        let utf8FileName = utf8Component[..<lastDot]
+        // Guard against "." and ".." file names
+        if (utf8FileName.count == 1 || utf8FileName.count == 2) && utf8FileName.allSatisfy({ $0 == ._dot }) {
+            return ""
+        }
+        let result = String(lastPathComponent[utf8Component.index(after: lastDot)...])
         guard validatePathExtension(result) else {
             return ""
         }
diff --git a/Tests/FoundationEssentialsTests/StringTests.swift b/Tests/FoundationEssentialsTests/StringTests.swift
index 1bb5fb510..26286be15 100644
--- a/Tests/FoundationEssentialsTests/StringTests.swift
+++ b/Tests/FoundationEssentialsTests/StringTests.swift
@@ -854,16 +854,29 @@ private struct StringTests {
         #expect("/foo/bar/.zip".deletingPathExtension() == "/foo/bar/.zip")
         #expect("..".deletingPathExtension() == "..")
         #expect("..zip".deletingPathExtension() == "..zip")
+        #expect("/..".deletingPathExtension() == "/..")
+        #expect("/..zip".deletingPathExtension() == "/..zip")
         #expect("/foo/bar/..zip".deletingPathExtension() == "/foo/bar/..zip")
         #expect("/foo/bar/baz..zip".deletingPathExtension() == "/foo/bar/baz.")
         #expect("...".deletingPathExtension() == "...")
         #expect("...zip".deletingPathExtension() == "...zip")
+        #expect("/...".deletingPathExtension() == "/...")
+        #expect("/...zip".deletingPathExtension() == "/...zip")
         #expect("/foo/bar/...zip".deletingPathExtension() == "/foo/bar/...zip")
         #expect("/foo/bar/baz...zip".deletingPathExtension() == "/foo/bar/baz..")
         #expect("/foo.bar/bar.baz/baz.zip".deletingPathExtension() == "/foo.bar/bar.baz/baz")
         #expect("/.././.././a.zip".deletingPathExtension() == "/.././.././a")
         #expect("/.././.././.".deletingPathExtension() == "/.././.././.")
 
+        // File names starting with "." or ".." are OK
+        // as long as they aren't exactly "." or ".."
+        #expect("..name.txt".deletingPathExtension() == "..name")
+        #expect("/..name.txt".deletingPathExtension() == "/..name")
+        #expect("....txt".deletingPathExtension() == "...")
+        #expect("/....txt".deletingPathExtension() == "/...")
+        #expect(".name.txt".deletingPathExtension() == ".name")
+        #expect("/.name.txt".deletingPathExtension() == "/.name")
+
         #expect("path.foo".deletingPathExtension() == "path")
         #expect("path.foo.zip".deletingPathExtension() == "path.foo")
         #expect("/path.foo".deletingPathExtension() == "/path")