fix(tarballs): use correct top-level directory name in sdists

src/fromager/sources.py

@@ -534,8 +534,8 @@ def default_build_sdist(
     #
     # For cases where the PEP 517 approach works, use
     # pep517_build_sdist().
-    normalized_name = canonicalize_name(req.name).replace("-", "_")
-    sdist_filename = ctx.sdists_builds / f"{normalized_name}-{version}.tar.gz"
+    dist_name = canonicalize_name(req.name).replace("-", "_")
+    sdist_filename = ctx.sdists_builds / f"{dist_name}-{version}.tar.gz"
     if sdist_filename.exists():
         sdist_filename.unlink()
     ensure_pkg_info(
@@ -552,6 +552,7 @@ def default_build_sdist(
             tar=sdist,
             basedir=build_dir,
             prefix=build_dir.parent,
+            arcname_root=f"{dist_name}-{version}",
         )
     return sdist_filename
 

src/fromager/tarballs.py

@@ -30,12 +30,17 @@ def tar_reproducible(
     prefix: pathlib.Path | None = None,
     *,
     exclude_vcs: bool = False,
+    arcname_root: str | None = None,
 ) -> None:
     """Create reproducible tar file
 
     Add content from basedir to already opened tar. If prefix is provided, use
     it to set relative paths for the content being added.
 
+    If arcname_root is provided, prepend it to all archive entry names.
+    This allows the top-level directory to be explicitly set regardless of
+    the basedir or prefix.
+
     If ``exclude_vcs`` is True, then Bazaar, git, Mercurial, and subversion
     directories and files are excluded.
     """
@@ -53,7 +58,13 @@ def tar_reproducible(
     content.sort()
 
     for fn in content:
-        # Ensure that the paths in the tarfile are rooted at the prefix
-        # directory, if we have one.
-        arcname = fn if prefix is None else os.path.relpath(fn, prefix)
+        if arcname_root is not None:
+            # When arcname_root is specified, compute paths relative to basedir
+            # to avoid including intermediate directory names from build_dir
+            rel = os.path.relpath(fn, basedir)
+            arcname = arcname_root if rel == "." else os.path.join(arcname_root, rel)
+        else:
+            # Ensure that the paths in the tarfile are rooted at the prefix
+            # directory, if we have one.
+            arcname = fn if prefix is None else os.path.relpath(fn, prefix)
         tar.add(fn, filter=_tar_reset, recursive=False, arcname=arcname)

tests/test_sources.py

@@ -786,3 +786,38 @@ def test_default_build_sdist_normalizes_filename(
                 expected_filename = f"{expected_filename_part}-1.0.0.tar.gz"
                 assert sdist_file.name == expected_filename
                 assert sdist_file.parent == tmp_context.sdists_builds
+
+
+def test_default_build_sdist_normalizes_name_and_root(
+    tmp_context: context.WorkContext,
+    tmp_path: pathlib.Path,
+) -> None:
+    """Verify the sdist filename and archive root for a monorepo package."""
+    sdist_root = tmp_path / "Foo.Bar-1.0"
+    build_dir = sdist_root / "src"
+    build_dir.mkdir(parents=True)
+    (build_dir / "setup.py").write_text("from setuptools import setup; setup()\n")
+    (build_dir / "module.py").write_text("# module\n")
+
+    req = Requirement("Foo.Bar==1.0")
+    version = Version("1.0")
+    build_env = Mock()
+
+    sdist_file = sources.default_build_sdist(
+        ctx=tmp_context,
+        extra_environ={},
+        req=req,
+        version=version,
+        sdist_root_dir=sdist_root,
+        build_env=build_env,
+        build_dir=build_dir,
+    )
+
+    assert sdist_file.name == "foo_bar-1.0.tar.gz"
+    assert sdist_file.parent == tmp_context.sdists_builds
+
+    with tarfile.open(sdist_file, "r:gz") as tar:
+        names = tar.getnames()
+        top_levels = {name.split("/")[0] for name in names}
+        assert top_levels == {"foo_bar-1.0"}
+        assert "foo_bar-1.0/setup.py" in names

tests/test_tarballs.py

@@ -93,3 +93,34 @@ def test_vcs_exclude(tmp_path: pathlib.Path) -> None:
     with tarfile.open(t1, "r") as tf:
         names = tf.getnames()
     assert names == [str(p).lstrip(os.sep) for p in [root, root / "a"]]
+
+
+def test_arcname_root(tmp_path: pathlib.Path) -> None:
+    """Test that arcname_root sets the top-level directory name.
+
+    This reproduces issue #1315: when basedir is a subdirectory (monorepo case),
+    arcname_root should ensure the top-level archive entry is {name}-{version},
+    not the basedir's name.
+    """
+    # Simulate a monorepo structure: mypkg-1.0/python/
+    sdist_root = tmp_path / "mypkg-1.0"
+    build_dir = sdist_root / "python"
+    build_dir.mkdir(parents=True)
+    (build_dir / "setup.py").write_text("from setuptools import setup; setup()\n")
+
+    t1 = tmp_path / "out.tar"
+    with tarfile.open(t1, "w") as tf:
+        tarballs.tar_reproducible(
+            tar=tf,
+            basedir=build_dir,
+            prefix=sdist_root,
+            arcname_root="mypkg-1.0",
+        )
+    with tarfile.open(t1, "r") as tf:
+        names = tf.getnames()
+
+    # All entries should be rooted at mypkg-1.0, not python/
+    # This ensures the sdist unpacks to mypkg-1.0/, not python/
+    assert "mypkg-1.0" in names[0]
+    assert "python" not in names[0]  # build_dir's name should not appear
+    assert "mypkg-1.0/setup.py" in names