Merge pull request #361 from takluyver/build-deps-maybe

Provide build requirements only if module needs to be imported for version or docstring

flit_core/flit_core/buildapi.py

@@ -5,7 +5,10 @@
 import os.path as osp
 from pathlib import Path
 
-from .common import Module, make_metadata, write_entry_points, dist_info_name
+from .common import (
+    Module, make_metadata, write_entry_points, dist_info_name,
+    get_docstring_and_version_via_ast,
+)
 from .config import read_flit_config
 from .wheel import make_wheel_in, _write_wheel_file
 from .sdist import SdistBuilder
@@ -18,9 +21,17 @@
 def get_requires_for_build_wheel(config_settings=None):
     """Returns a list of requirements for building, as strings"""
     info = read_flit_config(pyproj_toml)
-    return info.metadata.get('requires_dist', [])
+    # If we can get the module info from the AST, we don't need any extra
+    # dependencies. If not, we'll need to try importing it, so report any
+    # runtime dependencies as build dependencies.
+    module = Module(info.module, Path.cwd())
+    docstring, version = get_docstring_and_version_via_ast(module)
+    if (docstring is None) or (version is None):
+        return info.metadata.get('requires_dist', [])
+    else:
+        return []
 
-# For now, we require all dependencies to build either a wheel or an sdist.
+# Requirements to build an sdist are the same as for a wheel
 get_requires_for_build_sdist = get_requires_for_build_wheel
 
 def prepare_metadata_for_build_wheel(metadata_directory, config_settings=None):

flit_core/flit_core/tests/samples/constructed_version/pyproject.toml

@@ -0,0 +1,12 @@
+[build-system]
+requires = ["flit_core >=2,<4"]
+build-backend = "flit_core.buildapi"
+
+[tool.flit.metadata]
+module = "module1"
+author = "Sir Robin"
+author-email = "robin@camelot.uk"
+home-page = "http://github.com/sirrobin/module1"
+requires = [
+    "numpy >=1.16.0",
+]

flit_core/flit_core/tests/test_buildapi.py

@@ -20,8 +20,17 @@ def cwd(directory):
         os.chdir(prev)
 
 def test_get_build_requires():
-    expected = ["requests >= 2.18", "docutils"]
+    # This module can be inspected (for docstring & __version__) without
+    # importing it, so there are no build dependencies.
     with cwd(osp.join(samples_dir,'pep517')):
+        assert buildapi.get_requires_for_build_wheel() == []
+        assert buildapi.get_requires_for_build_sdist() == []
+
+def test_get_build_requires_import():
+    # This one has to be imported, so its runtime dependencies are also
+    # build dependencies.
+    expected = ["numpy >=1.16.0"]
+    with cwd(osp.join(samples_dir, 'constructed_version')):
         assert buildapi.get_requires_for_build_wheel() == expected
         assert buildapi.get_requires_for_build_sdist() == expected
 

flit_core/flit_core/tests/test_common.py

@@ -50,7 +50,7 @@ def test_get_info_from_module(self):
                                 'version': '0.1'}
                          )
 
-        info = get_info_from_module(Module('modulewithconstructedversion', samples_dir))
+        info = get_info_from_module(Module('module1', samples_dir / 'constructed_version'))
         self.assertEqual(info, {'summary': 'This module has a __version__ that requires runtime interpretation',
                                 'version': '1.2.3'}
                          )