feat: Add support for dependency groups which include other groups only

Author: finswimmer

src/poetry/core/factory.py

@@ -347,7 +347,7 @@ def _configure_package_dependencies(
                 cls._add_package_group_dependencies(
                     package=package,
                     group=group,
-                    dependencies=group_config["dependencies"],
+                    dependencies=group_config.get("dependencies", {}),
                 )
 
             for group_name, group_config in tool_poetry["group"].items():

src/poetry/core/json/schemas/poetry-schema.json

@@ -171,8 +171,17 @@
         "^[a-zA-Z-_.0-9]+$": {
           "type": "object",
           "description": "This represents a single dependency group",
-          "required": [
-            "dependencies"
+          "anyOf": [
+            {
+              "required": [
+                "dependencies"
+              ]
+            },
+            {
+              "required": [
+                "include-groups"
+              ]
+            }
           ],
           "properties": {
             "optional": {

tests/fixtures/project_with_included_groups_only/README.rst

@@ -0,0 +1,2 @@
+My Package
+==========

tests/fixtures/project_with_included_groups_only/pyproject.toml

@@ -0,0 +1,37 @@
+[tool.poetry]
+name = "simple-project"
+version = "1.2.3"
+description = "Some description."
+authors = [
+    "Sébastien Eustace <sebastien@eustace.io>"
+]
+license = "MIT"
+
+readme = "README.rst"
+
+homepage = "https://python-poetry.org"
+repository = "https://github.com/python-poetry/poetry"
+documentation = "https://python-poetry.org/docs"
+
+keywords = ["packaging", "dependency", "poetry"]
+
+classifiers = [
+    "Topic :: Software Development :: Build Tools",
+    "Topic :: Software Development :: Libraries :: Python Modules"
+]
+
+# Requirements
+[tool.poetry.dependencies]
+python = "~2.7 || ^3.4"
+
+[tool.poetry.group.lint.dependencies]
+black = "*"
+
+[tool.poetry.group.testing.dependencies]
+pytest = "*"
+
+[tool.poetry.group.all]
+include-groups = [
+    "lint",
+    "testing",
+]

tests/fixtures/project_with_included_groups_only/simple_project/__init__.py

@@ -1094,3 +1094,16 @@ def test_create_poetry_with_unknown_nested_dependency_groups() -> None:
         ValueError, match="Group 'dev' includes group 'testing' which is not defined"
     ):
         _ = Factory().create_poetry(fixtures_dir / "project_with_unknown_nested_group")
+
+
+def test_create_poetry_with_included_groups_only() -> None:
+    poetry = Factory().create_poetry(fixtures_dir / "project_with_included_groups_only")
+    assert len(poetry.package.all_requires) == 4
+    assert [
+        (dep.name, ",".join(dep.groups)) for dep in poetry.package.all_requires
+    ] == [
+        ("black", "lint"),
+        ("pytest", "testing"),
+        ("black", "all"),
+        ("pytest", "all"),
+    ]