From c23432ac41385b224681fd286283b4ba88fec978 Mon Sep 17 00:00:00 2001
From: George Macon <george.macon@gtri.gatech.edu>
Date: Wed, 3 May 2023 11:47:36 -0400
Subject: [PATCH] Keep a trailing slash in URL.joinpath

Issue: #862
---
 CHANGES/862.bugfix.rst |  1 +
 tests/test_url.py      | 18 ++++++++++++++++++
 yarl/_url.py           |  3 ++-
 3 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 CHANGES/862.bugfix.rst

diff --git a/CHANGES/862.bugfix.rst b/CHANGES/862.bugfix.rst
new file mode 100644
index 000000000..04bff12f5
--- /dev/null
+++ b/CHANGES/862.bugfix.rst
@@ -0,0 +1 @@
+Stopped dropping trailing slashes in ``URL.joinpath``.
diff --git a/tests/test_url.py b/tests/test_url.py
index 261bb562b..814d2c28b 100644
--- a/tests/test_url.py
+++ b/tests/test_url.py
@@ -797,6 +797,21 @@ def test_div_with_dots():
             "http://example.com/path/to",
             id="cleanup-query-and-fragment",
         ),
+        pytest.param("", ("path/",), "http://example.com/path/", id="trailing-slash"),
+        pytest.param(
+            "", ("path/", "to/"), "http://example.com/path/to/", id="duplicate-slash"
+        ),
+        pytest.param("", (), "http://example.com", id="empty-segments"),
+        pytest.param(
+            "/", ("path/",), "http://example.com/path/", id="base-slash-trailing-slash"
+        ),
+        pytest.param(
+            "/",
+            ("path/", "to/"),
+            "http://example.com/path/to/",
+            id="base-slash-duplicate-slash",
+        ),
+        pytest.param("/", (), "http://example.com", id="base-slash-empty-segments"),
     ],
 )
 def test_joinpath(base, to_join, expected):
@@ -811,6 +826,9 @@ def test_joinpath(base, to_join, expected):
         pytest.param(URL("a"), ("b",), ("a", "b"), id="relative-path"),
         pytest.param(URL("a"), ("b", "", "c"), ("a", "b", "c"), id="empty-element"),
         pytest.param(URL("/a"), ("b"), ("/", "a", "b"), id="absolute-path"),
+        pytest.param(URL(), ("a/",), ("a", ""), id="trailing-slash"),
+        pytest.param(URL(), ("a/", "b/"), ("a", "b", ""), id="duplicate-slash"),
+        pytest.param(URL(), (), ("",), id="empty-segments"),
     ],
 )
 def test_joinpath_relative(url, to_join, expected):
diff --git a/yarl/_url.py b/yarl/_url.py
index 3e1c1a7f5..1507e9c8c 100644
--- a/yarl/_url.py
+++ b/yarl/_url.py
@@ -713,7 +713,8 @@ def _validate_authority_uri_abs_path(host, path):
 
     def _make_child(self, segments, encoded=False):
         """add segments to self._val.path, accounting for absolute vs relative paths"""
-        parsed = []
+        # keep the trailing slash if the last segment ends with /
+        parsed = [""] if segments and segments[-1][-1:] == "/" else []
         for seg in reversed(segments):
             if not seg:
                 continue