feat: out-of-box stubs package support (#280)

* out-of-box stubs package support

* Update pyproject.toml

Author: trim21

src/pdm/backend/utils.py

@@ -44,7 +44,12 @@ def is_python_package(fullpath: str) -> bool:
         return False
     if os.path.basename(fullpath.rstrip("/")) in ("__pycache__", "__pypackages__"):
         return False
-    return os.path.isfile(os.path.join(fullpath, "__init__.py"))
+    if os.path.isfile(os.path.join(fullpath, "__init__.py")):
+        return True
+    # stubs
+    return os.path.basename(fullpath).endswith("-stubs") and os.path.isfile(
+        os.path.join(fullpath, "__init__.pyi")
+    )
 
 
 def merge_marker(requirement: Requirement, marker: str) -> None:

tests/fixtures/projects/demo-package-stubs/LICENSE

@@ -0,0 +1 @@
+MIT License

tests/fixtures/projects/demo-package-stubs/README.md

@@ -0,0 +1 @@
+# This is a demo module for a stub package

tests/fixtures/projects/demo-package-stubs/pyproject.toml

@@ -0,0 +1,15 @@
+[build-system]
+requires = ["pdm-backend"]
+build-backend = "pdm.backend"
+
+[project]
+authors = [
+    {name = "frostming", email = "[email protected]"},
+]
+version = '0.0.0'
+requires-python = ">=2.7"
+license = "MIT"
+dependencies = ["flask"]
+description = ""
+name = "demo-package-stubs"
+readme = "README.md"

tests/fixtures/projects/demo-package-stubs/src/my_package-stubs/__init__.pyi

@@ -0,0 +1 @@
+def hello_world() -> None: ...