From aa6245bf5152131ad1af5a24ee2da09a3ee325e6 Mon Sep 17 00:00:00 2001
From: Alex Lorenz <arphaman@gmail.com>
Date: Thu, 1 Aug 2024 20:39:58 -0700
Subject: [PATCH 1/2] [windows] path: drop the trailing backslash before
 invoking PathCchRemoveFileSpec to compute the dirname

PathCchRemoveFileSpec's is documented to not remove the file spec if it comes with a backslash suffix. Thus, we should remove the trailing backslashes before calling this API, to ensure we actually drop the current file/directory name
---
 Sources/TSCBasic/Path.swift         | 16 +++++++++++++++-
 Tests/TSCBasicTests/PathTests.swift |  8 ++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/Sources/TSCBasic/Path.swift b/Sources/TSCBasic/Path.swift
index 3ceb2252..208f9819 100644
--- a/Sources/TSCBasic/Path.swift
+++ b/Sources/TSCBasic/Path.swift
@@ -461,7 +461,21 @@ private struct WindowsPath: Path, Sendable {
         let fsr: UnsafePointer<Int8> = self.string.fileSystemRepresentation
         defer { fsr.deallocate() }
 
-        let path: String = String(cString: fsr)
+        var path: String = String(cString: fsr)
+        // PathCchRemoveFileSpec removes trailing '\' for a
+        // path like 'c:\root\path\', which doesn't give us the parent
+        // directory name. Thus, drop the trailing '\' before calling
+        // PathCchRemoveFileSpec.
+        var substring = path[path.startIndex..<path.endIndex]
+        while !substring.isEmpty && substring.utf8.last == UInt8(ascii: "\\") {
+            substring = substring.dropLast()
+        }
+        if !substring.isEmpty && substring.last != ":" {
+            // Drop the trailing '\', unless the string path only
+            // has '\', and unless the slashes are right after the drive letter.
+            path = String(substring)
+        }
+
         return path.withCString(encodedAs: UTF16.self) {
             let data = UnsafeMutablePointer(mutating: $0)
             PathCchRemoveFileSpec(data, path.count)
diff --git a/Tests/TSCBasicTests/PathTests.swift b/Tests/TSCBasicTests/PathTests.swift
index 450aa29e..d9b85be4 100644
--- a/Tests/TSCBasicTests/PathTests.swift
+++ b/Tests/TSCBasicTests/PathTests.swift
@@ -131,6 +131,14 @@ class PathTests: XCTestCase {
         XCTAssertEqual(RelativePath("abc").dirname, ".")
         XCTAssertEqual(RelativePath("").dirname, ".")
         XCTAssertEqual(RelativePath(".").dirname, ".")
+#if os(Windows)
+        XCTAssertEqual(AbsolutePath("C:\\a\\b").dirname, "C:\\a")
+        XCTAssertEqual(AbsolutePath("C:\\").dirname, "C:\\")
+        XCTAssertEqual(AbsolutePath("C:\\\\").dirname, "C:\\\\")
+        XCTAssertEqual(AbsolutePath("C:\\a\\b\\").dirname, "C:\\a")
+        XCTAssertEqual(AbsolutePath("C:\\a\\b\\\\").dirname, "C:\\a")
+        XCTAssertEqual(AbsolutePath("C:\\a\\").dirname, "C:\\")
+#endif
     }
 
     func testBaseNameExtraction() {

From 53cabc89f27008f946ea041dc844e08ba4a9f769 Mon Sep 17 00:00:00 2001
From: Alex Lorenz <arphaman@gmail.com>
Date: Fri, 2 Aug 2024 13:51:11 -0700
Subject: [PATCH 2/2] Test C:\\\ case

---
 Tests/TSCBasicTests/PathTests.swift | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Tests/TSCBasicTests/PathTests.swift b/Tests/TSCBasicTests/PathTests.swift
index d9b85be4..d18ce814 100644
--- a/Tests/TSCBasicTests/PathTests.swift
+++ b/Tests/TSCBasicTests/PathTests.swift
@@ -134,7 +134,8 @@ class PathTests: XCTestCase {
 #if os(Windows)
         XCTAssertEqual(AbsolutePath("C:\\a\\b").dirname, "C:\\a")
         XCTAssertEqual(AbsolutePath("C:\\").dirname, "C:\\")
-        XCTAssertEqual(AbsolutePath("C:\\\\").dirname, "C:\\\\")
+        XCTAssertEqual(AbsolutePath("C:\\\\").dirname, "C:\\")
+        XCTAssertEqual(AbsolutePath("C:\\\\\\").dirname, "C:\\")
         XCTAssertEqual(AbsolutePath("C:\\a\\b\\").dirname, "C:\\a")
         XCTAssertEqual(AbsolutePath("C:\\a\\b\\\\").dirname, "C:\\a")
         XCTAssertEqual(AbsolutePath("C:\\a\\").dirname, "C:\\")