Correct handling of pyproject.toml files lacking a [project] section

src/incremental/__init__.py

@@ -482,11 +482,20 @@ def _load_pyproject_toml(toml_path):  # type: (str) -> Optional[_IncrementalConf
 
     tool_incremental = _extract_tool_incremental(data)
 
-    if tool_incremental is None or tool_incremental == {}:
+    package = None
+    if tool_incremental is not None and "name" in tool_incremental:
+        package = tool_incremental["name"]
+    if package is None:
         try:
             package = data["project"]["name"]
         except KeyError:
-            raise ValueError("""\
+            pass
+    if package is None:
+        # We can't proceed without a project name, but that's only an error
+        # if [tool.incremental] is present.
+        if tool_incremental is None:
+            return None
+        raise ValueError("""\
 Couldn't extract the package name from pyproject.toml. Specify it like:
 
     [project]
@@ -496,12 +505,8 @@ def _load_pyproject_toml(toml_path):  # type: (str) -> Optional[_IncrementalConf
 
     [tool.incremental]
     name = "Foo"
-""")
-    elif tool_incremental.keys() == {"name"}:
-        package = tool_incremental["name"]
-    else:
-        raise ValueError("Unexpected key(s) in [tool.incremental]")
 
+""")
     if not isinstance(package, str):
         raise TypeError(
             "Package name must be a string, but found {}".format(type(package))
@@ -526,6 +531,8 @@ def _extract_tool_incremental(data):  # type: (Dict[str, object]) -> Optional[Di
     if not isinstance(tool_incremental, dict):
         raise ValueError("[tool.incremental] must be a table")
 
+    if not {"name"}.issuperset(tool_incremental.keys()):
+        raise ValueError("Unexpected key(s) in [tool.incremental]")
     return tool_incremental
 
 

src/incremental/newsfragments/100.bugfix

@@ -0,0 +1 @@
+Incremental 24.7.0 would produce an error when parsing the ``pyproject.toml`` of a project that lacked the ``use_incremental=True`` or ``[tool.incremental]`` opt-in markers if that file lacked a ``[project]`` section containing the package name. This could cause a project that only uses ``pyproject.toml`` to configure tools to fail to build if Incremental is installed. Incremental now ignores such projects.

src/incremental/tests/test_pyproject.py

@@ -49,14 +49,24 @@ def test_fileNotFound(self):
         path = os.path.join(cast(str, self.mktemp()), "pyproject.toml")
         self.assertIsNone(_load_pyproject_toml(path))
 
-    def test_nameMissing(self):
+    def test_configMissing(self):
         """
-        `ValueError` is raised when ``[tool.incremental]`` is present but
-        he project name isn't available.
+        A ``pyproject.toml`` that exists but provides no relevant configuration
+        is ignored.
         """
         for toml in [
             "\n",
             "[tool.notincremental]\n",
+            "[project]\n",
+        ]:
+            self.assertIsNone(self._loadToml(toml))
+
+    def test_nameMissing(self):
+        """
+        `ValueError` is raised when ``[tool.incremental]`` is present but
+        the project name isn't available.
+        """
+        for toml in [
             "[tool.incremental]\n",
             "[project]\n[tool.incremental]\n",
         ]:

tests/example_noop/example_noop/__init__.py

@@ -0,0 +1,11 @@
+"""
+An example setuptools project that doesn't use Incremental at all.
+
+This is used to verify that Incremental correctly deactivates itself
+when there is no opt-in, even though setuptools always invokes its
+hook.
+"""
+
+__version__ = "100"
+
+__all__ = ["__version__"]

tests/example_noop/pyproject.toml

@@ -0,0 +1,3 @@
+# This file exists, but doesn't contain any [project] or
+# [tool.incremental] configuration so Incremental ignores it.
+[tool.something]

tests/example_noop/setup.py

@@ -0,0 +1,13 @@
+from setuptools import setup
+
+setup(
+    name="example_noop",
+    version="100",
+    packages=["example_noop"],
+    zip_safe=False,
+    setup_requires=[
+        # Ensure Incremental is installed for test purposes
+        # (but it won't do anything).
+        "incremental",
+    ],
+)

tests/test_examples.py

@@ -97,3 +97,15 @@ def test_hatch_version_set(self):
             # Hatch may wrap the output, so we are flexible about the specifics of whitespace.
             suggestion.replace(b".", rb"\.").replace(b" ", b"\\s+"),
         )
+
+    def test_noop(self):
+        """
+        The Incremental setuptools hook is a silent no-op when there is no Incremental
+        configuration to be found.
+        """
+        build_and_install(TEST_DIR.child("example_noop"))
+
+        import example_noop
+
+        self.assertEqual(example_noop.__version__, "100")
+        self.assertEqual(metadata.version("example_noop"), "100")