From eccc6700dcf91db0b7e54c3ea7795c5d1ddd4bc9 Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Sun, 9 Nov 2025 21:45:19 +0100
Subject: [PATCH] - Fix appending to `c:\` or `\` #2569.

---
 lib/std/io/path.c3          |  4 +---
 releasenotes.md             |  1 +
 test/unit/stdlib/io/path.c3 | 13 +++++++++++++
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/lib/std/io/path.c3 b/lib/std/io/path.c3
index d98251018..858dbda0e 100644
--- a/lib/std/io/path.c3
+++ b/lib/std/io/path.c3
@@ -186,13 +186,11 @@ fn bool Path.equals(self, Path p2) @operator(==)
 fn Path? Path.append(self, Allocator allocator, String filename)
 {
 	if (!self.path_string.len) return new(allocator, filename, self.env)!;
-	assert(!is_separator(self.path_string[^1], self.env));
-
 	@pool()
 	{
 		DString dstr = dstring::temp_with_capacity(self.path_string.len + 1 + filename.len);
 		dstr.append(self.path_string);
-		dstr.append(PREFERRED_SEPARATOR);
+		if (!is_separator(self.path_string[^1], self.env)) dstr.append(PREFERRED_SEPARATOR);
 		dstr.append(filename);
 		return new(allocator, dstr.str_view(), self.env);
 	};
diff --git a/releasenotes.md b/releasenotes.md
index 48d25ab1a..677634f3d 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -19,6 +19,7 @@
 - Passing a compile time type implicitly converted to a typeid would crash instead of producing an error. #2568
 - Compiler assert with const enum based on vector #2566
 - Fix to `Path` handling `c:\foo` and `\home` parent. #2569
+- Fix appending to `c:\` or `\` #2569.
 
 ### Stdlib changes
 
diff --git a/test/unit/stdlib/io/path.c3 b/test/unit/stdlib/io/path.c3
index e77d2b5ec..fdc86b2d6 100644
--- a/test/unit/stdlib/io/path.c3
+++ b/test/unit/stdlib/io/path.c3
@@ -1,5 +1,18 @@
 module std::io::path @test;
 
+fn void test_append()
+{
+	Path p = path::new(mem, "/", POSIX)!!;
+	Path p2 = p.append(mem, "hello")!!;
+	test::eq(p2.str_view(), "/hello");
+	p.free();
+	p2.free();
+	p = path::new(mem, "c:\\", WIN32)!!;
+	p2 = p.append(mem, "hello")!!;
+	assert(p2.str_view() == "c:\\hello");
+	p.free();
+	p2.free();
+}
 fn void test_dot()
 {
 	Path p = path::new(mem, ".")!!;