Add an end-to-end test for config settings

tests/functional/test_config_settings.py

@@ -0,0 +1,103 @@
+import json
+from zipfile import ZipFile
+
+from tests.lib import PipTestEnvironment
+
+PYPROJECT_TOML = """\
+[build-system]
+requires = []
+build-backend = "example:main"
+backend-path = ["backend"]
+"""
+
+BACKEND_SRC = '''\
+import csv
+import json
+import os.path
+from zipfile import ZipFile
+import hashlib
+import base64
+import io
+
+WHEEL = """\
+Wheel-Version: 1.0
+Generator: example 1.0
+Root-Is-Purelib: true
+Tag: py3-none-any
+"""
+
+METADATA = """\
+Metadata-Version: 2.1
+Name: {name}
+Version: {version}
+Summary: A dummy package
+Author: None
+Author-email: none@example.org
+License: MIT
+"""
+
+def make_wheel(z, project, version, files):
+    record = []
+    def add_file(name, data):
+        data = data.encode("utf-8")
+        z.writestr(name, data)
+        digest = hashlib.sha256(data).digest()
+        hash = base64.urlsafe_b64encode(digest).rstrip(b"=").decode("ASCII")
+        record.append((name, f"sha256={hash}", len(data)))
+    distinfo = f"{project}-{version}.dist-info"
+    add_file(f"{distinfo}/WHEEL", WHEEL)
+    add_file(f"{distinfo}/METADATA", METADATA.format(name=project, version=version))
+    for name, data in files:
+        add_file(name, data)
+    record_name = f"{distinfo}/RECORD"
+    record.append((record_name, "", ""))
+    b = io.BytesIO()
+    rec = io.TextIOWrapper(b, newline="", encoding="utf-8")
+    w = csv.writer(rec)
+    w.writerows(record)
+    z.writestr(record_name, b.getvalue())
+    rec.close()
+
+
+class Backend:
+    def build_wheel(
+        self,
+        wheel_directory,
+        config_settings=None,
+        metadata_directory=None
+    ):
+        if config_settings is None:
+            config_settings = {}
+        print("CONFIG SETTINGS IN BACKEND", config_settings)
+        w = os.path.join(wheel_directory, "foo-1.0-py3-none-any.whl")
+        with open(w, "wb") as f:
+            with ZipFile(f, "w") as z:
+                make_wheel(
+                    z, "foo", "1.0",
+                    [("config.json", json.dumps(config_settings))]
+                )
+        return "foo-1.0-py3-none-any.whl"
+
+main = Backend()
+'''
+
+
+def test_backend_sees_config(script: PipTestEnvironment) -> None:
+    example = script.scratch_path / "example"
+    example.mkdir(parents=True)
+    backend = example / "backend"
+    backend.mkdir()
+    (example / "pyproject.toml").write_text(PYPROJECT_TOML)
+    (backend / "example.py").write_text(BACKEND_SRC)
+    script.pip(
+        "wheel",
+        "--config-settings",
+        "FOO=Hello",
+        "./example",
+    )
+    wheel_file_name = "foo-1.0-py3-none-any.whl"
+    wheel_file_path = script.cwd / wheel_file_name
+    with open(wheel_file_path, "rb") as f:
+        with ZipFile(f) as z:
+            output = z.read("config.json")
+            assert json.loads(output) == {"FOO": "Hello"}