with_path: preserve bare-relative status for netloc-less URLs (#1770)

CHANGES/1770.bugfix.rst

@@ -0,0 +1,10 @@
+Fixed :py:meth:`~yarl.URL.with_path` to preserve the bare-relative
+status of a URL when the new path is given without a leading ``/``.
+Previously ``URL("foo/bar").with_path("abs")`` silently returned
+``URL("/abs")`` (an absolute-path reference), which changes how the
+URL resolves against any base. The leading ``/`` is now only added
+for URLs that have a netloc, so ``URL("foo/bar").with_path("abs")``
+returns ``URL("abs")`` and ``URL("foo/bar").with_path("/abs")`` still
+returns ``URL("/abs")``.
+
+-- by :user:`HrachShah`.

docs/spelling_wordlist.txt

@@ -42,6 +42,7 @@ macOS
 mailto
 manylinux
 multi
+netloc
 nightlies
 pre
 pydantic

tests/test_url.py

@@ -1489,6 +1489,37 @@ def test_with_path_leading_slash() -> None:
     assert url.with_path("test").path == "/test"
 
 
+def test_with_path_preserves_bare_relative() -> None:
+    # Issue #1770: with_path must not silently promote a bare-relative
+    # URL (one without scheme/netloc) into an absolute-path reference
+    # when the new path does not start with "/".
+    url = URL("foo/bar")
+    new = url.with_path("abs")
+    assert str(new) == "abs"
+    assert new.raw_path == "abs"
+    assert not new.is_absolute()
+
+
+def test_with_path_explicit_slash_preserved_on_bare_relative() -> None:
+    # The same URL, with an explicit "/abs" path, must still produce
+    # the leading slash.
+    url = URL("foo/bar")
+    new = url.with_path("/abs")
+    assert str(new) == "/abs"
+    assert new.raw_path == "/abs"
+
+
+def test_with_path_no_netloc_join_round_trip() -> None:
+    # The original URL stays bare-relative across with_path, so the
+    # join round-trips through both directions without absorbing the
+    # leading-slash promotion from the previous behaviour.
+    url = URL("foo/bar")
+    new = url.with_path("abs")
+    assert new.join(URL("baz")) == URL("baz")
+    base = URL("http://example.com/x/y")
+    assert base.join(new) == URL("http://example.com/x/abs")
+
+
 # with_fragment
 
 

yarl/_url.py

@@ -1210,7 +1210,7 @@ def with_path(
             path = PATH_QUOTER(path)
             if netloc:
                 path = normalize_path(path) if "." in path else path
-        if path and path[0] != "/":
+        if path and path[0] != "/" and netloc:
             path = f"/{path}"
         query = self._query if keep_query else ""
         fragment = self._fragment if keep_fragment else ""