trust empty requires dist with modern metadata

src/poetry/inspection/info.py

@@ -14,6 +14,7 @@
 
 import pkginfo
 
+from poetry.core.constraints.version import Version
 from poetry.core.factory import Factory
 from poetry.core.packages.dependency import Dependency
 from poetry.core.packages.package import Package
@@ -246,9 +247,18 @@ def _from_distribution(
         :param dist: The distribution instance to parse information from.
         """
         requirements = None
+        dynamic_metadata = False
+
+        if dist.metadata_version is not None:
+            metadata_version = Version.parse(dist.metadata_version)
+            dynamic_metadata_introduced = Version.parse("2.2")
+            dynamic_metadata = metadata_version >= dynamic_metadata_introduced
 
         if dist.requires_dist:
             requirements = list(dist.requires_dist)
+        elif dynamic_metadata and "Requires-Dist" not in dist.dynamic:
+            # We can trust the metadata when it says that requires_dist is empty.
+            requirements = []
         else:
             requires = Path(dist.filename) / "requires.txt"
             if requires.exists():

tests/fixtures/inspection/demo_no_setup_pkg_info_no_deps_dynamic/PKG-INFO

@@ -0,0 +1,11 @@
+Metadata-Version: 2.2
+Name: demo
+Version: 0.1.0
+Summary: Demo project.
+Home-page: https://github.com/demo/demo
+Author: Sébastien Eustace
+Author-email: sebastien@eustace.io
+License: MIT
+Description: UNKNOWN
+Platform: UNKNOWN
+Dynamic: Requires-Dist

tests/fixtures/inspection/demo_no_setup_pkg_info_no_deps_dynamic/pyproject.toml

@@ -0,0 +1,19 @@
+# this was copied over and modified from orjson project's pyproject.toml
+# https://github.com/ijl/orjson/blob/master/pyproject.toml
+[project]
+name = "demo"
+repository = "https://github.com/demo/demo"
+
+[build-system]
+build-backend = "maturin"
+requires = ["maturin>=0.8.1,<0.9"]
+
+[tool.maturin]
+manylinux = "off"
+sdist-include = ["Cargo.lock", "json/**/*"]
+strip = "on"
+
+[tool.black]
+line-length = 88
+target-version = ['py36', 'py37', 'py38']
+include = '\.pyi?$'

tests/fixtures/inspection/demo_no_setup_pkg_info_no_deps_for_sure/PKG-INFO

@@ -0,0 +1,10 @@
+Metadata-Version: 2.2
+Name: demo
+Version: 0.1.0
+Summary: Demo project.
+Home-page: https://github.com/demo/demo
+Author: Sébastien Eustace
+Author-email: sebastien@eustace.io
+License: MIT
+Description: UNKNOWN
+Platform: UNKNOWN

tests/fixtures/inspection/demo_no_setup_pkg_info_no_deps_for_sure/pyproject.toml

@@ -0,0 +1,19 @@
+# this was copied over and modified from orjson project's pyproject.toml
+# https://github.com/ijl/orjson/blob/master/pyproject.toml
+[project]
+name = "demo"
+repository = "https://github.com/demo/demo"
+
+[build-system]
+build-backend = "maturin"
+requires = ["maturin>=0.8.1,<0.9"]
+
+[tool.maturin]
+manylinux = "off"
+sdist-include = ["Cargo.lock", "json/**/*"]
+strip = "on"
+
+[tool.black]
+line-length = 88
+target-version = ['py36', 'py37', 'py38']
+include = '\.pyi?$'

tests/inspection/test_info.py

@@ -261,6 +261,26 @@ def test_info_no_setup_pkg_info_no_deps(fixture_dir: FixtureDirGetter) -> None:
     assert info.requires_dist is None
 
 
+def test_info_no_setup_pkg_info_no_deps_for_sure(fixture_dir: FixtureDirGetter) -> None:
+    info = PackageInfo.from_directory(
+        fixture_dir("inspection") / "demo_no_setup_pkg_info_no_deps_for_sure",
+        disable_build=True,
+    )
+    assert info.name == "demo"
+    assert info.version == "0.1.0"
+    assert info.requires_dist == []
+
+
+def test_info_no_setup_pkg_info_no_deps_dynamic(fixture_dir: FixtureDirGetter) -> None:
+    info = PackageInfo.from_directory(
+        fixture_dir("inspection") / "demo_no_setup_pkg_info_no_deps_dynamic",
+        disable_build=True,
+    )
+    assert info.name == "demo"
+    assert info.version == "0.1.0"
+    assert info.requires_dist is None
+
+
 def test_info_setup_simple(mocker: MockerFixture, demo_setup: Path) -> None:
     spy = mocker.spy(VirtualEnv, "run")
     info = PackageInfo.from_directory(demo_setup)