Support build script in sub directory (#329)

src/poetry/core/masonry/builders/sdist.py

@@ -117,7 +117,9 @@ def build_setup(self) -> bytes:
 
         # If we have a build script, use it
         if self._package.build_script:
-            import_name = self._package.build_script.split(".")[0]
+            import_name = ".".join(
+                Path(self._package.build_script).with_suffix("").parts
+            )
             after += [f"from {import_name} import *", "build(setup_kwargs)"]
 
         modules = []

tests/masonry/builders/fixtures/build_script_in_subdir/pyproject.toml

@@ -0,0 +1,14 @@
+[tool.poetry]
+name = "build_script_in_subdir"
+version = "0.1"
+description = "Some description."
+authors = [
+    "Brandon Chinn <brandonchinn178@gmail.com>"
+]
+license = "MIT"
+homepage = "https://python-poetry.org/"
+packages = [
+    { include = "*", from = "src" },
+]
+
+build = "scripts/build.py"

tests/masonry/builders/test_sdist.py

@@ -360,6 +360,15 @@ def test_with_c_extensions_src_layout() -> None:
         assert "extended-0.1/src/extended/extended.c" in tar.getnames()
 
 
+def test_with_build_script_in_subdir() -> None:
+    poetry = Factory().create_poetry(project("build_script_in_subdir"))
+
+    builder = SdistBuilder(poetry)
+    setup = builder.build_setup()
+    # should not error
+    ast.parse(setup)
+
+
 def test_with_src_module_file() -> None:
     poetry = Factory().create_poetry(project("source_file"))