build: validate the source directory passed to ProjectBuilder

PR #260
Fixes #259

CHANGELOG.rst

@@ -3,6 +3,16 @@ Changelog
 +++++++++
 
 
+0.3.2 (XX-XX-2021)
+==================
+
+- Validate that the supplied source directory is valid (`PR #260`_, Fixes `#259`_)
+
+.. _PR #260: https://github.com/pypa/build/pull/260
+.. _#259: https://github.com/pypa/build/issues/259
+
+
+
 0.3.1 (09-03-2021)
 ==================
 

src/build/__init__.py

@@ -59,6 +59,16 @@ class TypoWarning(Warning):
     """
 
 
+def _validate_source_directory(srcdir):
+    # type: (str) -> None
+    if not os.path.isdir(srcdir):
+        raise BuildException('Source {} is not a directory'.format(srcdir))
+    pyproject_toml = os.path.join(srcdir, 'pyproject.toml')
+    setup_py = os.path.join(srcdir, 'setup.py')
+    if not os.path.exists(pyproject_toml) and not os.path.exists(setup_py):
+        raise BuildException('Source {} does not appear to be a Python project: no pyproject.toml or setup.py'.format(srcdir))
+
+
 def check_dependency(req_string, ancestral_req_strings=(), parent_extras=frozenset()):
     # type: (str, Tuple[str, ...], AbstractSet[str]) -> Iterator[Tuple[str, ...]]
     """
@@ -137,6 +147,7 @@ def __init__(self, srcdir, python_executable=sys.executable, scripts_dir=None):
         :param python_executable: The python executable where the backend lives
         """
         self.srcdir = os.path.abspath(srcdir)  # type: str
+        _validate_source_directory(srcdir)
 
         spec_file = os.path.join(srcdir, 'pyproject.toml')
 

tests/conftest.py

@@ -135,6 +135,11 @@ def test_no_backend_path(packages_path):
     return os.path.join(packages_path, 'test-no-backend')
 
 
+@pytest.fixture
+def test_no_project_path(packages_path):
+    return os.path.join(packages_path, 'test-no-project')
+
+
 @pytest.fixture
 def test_no_requires_path(packages_path):
     return os.path.join(packages_path, 'test-no-requires')

tests/test_projectbuilder.py

@@ -136,6 +136,18 @@ def test_check_dependency(monkeypatch, requirement_string, expected):
     assert next(build.check_dependency(requirement_string), None) == expected
 
 
+def test_bad_project(test_no_project_path):
+    # Passing a nonexistent project directory
+    with pytest.raises(build.BuildException):
+        build.ProjectBuilder(os.path.join(test_no_project_path, 'does-not-exist'))
+    # Passing a file as a project directory
+    with pytest.raises(build.BuildException):
+        build.ProjectBuilder(os.path.join(test_no_project_path, 'empty.txt'))
+    # Passing a project directory with no pyproject.toml or setup.py
+    with pytest.raises(build.BuildException):
+        build.ProjectBuilder(test_no_project_path)
+
+
 def test_init(mocker, test_flit_path, legacy_path, test_no_permission, test_bad_syntax_path):
     mocker.patch('pep517.wrappers.Pep517HookCaller')