1 files changed, 83 insertions, 2 deletions
diff --git a/src/bun.js/node/types.zig b/src/bun.js/node/types.zig
index d1c92e970..bc2144095 100644
--- a/src/bun.js/node/types.zig
+++ b/src/bun.js/node/types.zig
@@ -1682,6 +1682,87 @@ pub const Path = struct {
 
         return JSC.ZigString.init(out).withEncoding().toValueGC(globalThis);
     }
+
+    fn dirnameWindows(path: []const u8) []const u8 {
+        if (path.len == 0)
+            return ".";
+
+        const root_slice = std.fs.path.diskDesignatorWindows(path);
+        if (path.len == root_slice.len)
+            return root_slice;
+
+        const have_root_slash = path.len > root_slice.len and (path[root_slice.len] == '/' or path[root_slice.len] == '\\');
+
+        var end_index: usize = path.len - 1;
+
+        while (path[end_index] == '/' or path[end_index] == '\\') {
+            // e.g. '\\' => "\\"
+            if (end_index == 0) {
+                return path[0..1];
+            }
+            end_index -= 1;
+        }
+
+        while (path[end_index] != '/' and path[end_index] != '\\') {
+            if (end_index == 0) {
+                if (root_slice.len == 0) {
+                    return ".";
+                }
+                if (have_root_slash) {
+                    // e.g. "c:\\" => "c:\\"
+                    return path[0 .. root_slice.len + 1];
+                } else {
+                    // e.g. "c:foo" => "c:"
+                    return root_slice;
+                }
+            }
+            end_index -= 1;
+        }
+
+        if (have_root_slash and end_index == root_slice.len) {
+            end_index += 1;
+        }
+
+        return path[0..end_index];
+    }
+
+    fn dirnamePosix(path: []const u8) []const u8 {
+        if (path.len == 0)
+            return ".";
+
+        var end_index: usize = path.len - 1;
+
+        while (path[end_index] == '/') {
+            // e.g. "////" => "/"
+            if (end_index == 0) {
+                return "/";
+            }
+            end_index -= 1;
+        }
+
+        while (path[end_index] != '/') {
+            if (end_index == 0) {
+                // e.g. "a/", "a"
+                return ".";
+            }
+            end_index -= 1;
+        }
+
+        // e.g. "/a/" => "/"
+        if (end_index == 0 and path[0] == '/') {
+            return "/";
+        }
+
+        // "a/b" => "a" or "//b" => "//"
+        if (end_index <= 1) {
+            if (path[0] == '/' and path[1] == '/') {
+                end_index += 1;
+            }
+        }
+
+        return path[0..end_index];
+    }
+
     pub fn dirname(globalThis: *JSC.JSGlobalObject, isWindows: bool, args_ptr: [*]JSC.JSValue, args_len: u16) callconv(.C) JSC.JSValue {
         if (comptime is_bindgen) return JSC.JSValue.jsUndefined();
         if (args_len == 0) {
@@ -1697,9 +1778,9 @@ pub const Path = struct {
         const base_slice = path.slice();
 
         const out = if (isWindows)
-            std.fs.path.dirnameWindows(base_slice) orelse "."
+            @This().dirnameWindows(base_slice)
         else
-            std.fs.path.dirnamePosix(base_slice) orelse ".";
+            @This().dirnamePosix(base_slice);
 
         return JSC.ZigString.init(out).toValueGC(globalThis);
     }