Allowed fallback usage of project.name for name and package if pyproject.toml exists (#687)

Author: adiroiban

docs/configuration.rst

@@ -17,9 +17,8 @@ A minimal configuration for a Python project looks like this:
 .. code-block:: toml
 
    # pyproject.toml
-
-   [tool.towncrier]
-   package = "myproject"
+   [project]
+   name = "myproject"
 
 A minimal configuration for a non-Python project looks like this:
 
@@ -36,9 +35,9 @@ Top level keys
 ``name``
     The name of your project.
 
-    For Python projects that provide a ``package`` key, if left empty then the name will be automatically determined.
+    For Python projects that provide a ``package`` key, if left empty then the name will be automatically determined from the ``package`` key.
 
-    ``""`` by default.
+    Defaults to the key ``[project.name]`` in ``pyproject.toml`` (if present), otherwise defaults to the empty string ``""``.
 
 ``version``
     The version of your project.
@@ -167,6 +166,8 @@ Extra top level keys for Python projects
     Allows ``name`` and ``version`` to be automatically determined from the Python package.
     Changes the default ``directory`` to be a ``newsfragments`` directory within this package.
 
+    Defaults to the key ``[project.name]`` in ``pyproject.toml`` (if present), otherwise defaults to the empty string ``""``.
+
 ``package_dir``
     The folder your package lives.
 

src/towncrier/_settings/load.py

@@ -118,19 +118,44 @@ def load_config(directory: str) -> Config | None:
     towncrier_toml = os.path.join(directory, "towncrier.toml")
     pyproject_toml = os.path.join(directory, "pyproject.toml")
 
+    # In case the [tool.towncrier.name|package] is not specified
+    # we'll read it from [project.name]
+
+    if os.path.exists(pyproject_toml):
+        pyproject_config = load_toml_from_file(pyproject_toml)
+    else:
+        # make it empty so it won't be used as a backup plan
+        pyproject_config = {}
+
     if os.path.exists(towncrier_toml):
-        config_file = towncrier_toml
+        config_toml = towncrier_toml
     elif os.path.exists(pyproject_toml):
-        config_file = pyproject_toml
+        config_toml = pyproject_toml
     else:
         return None
 
-    return load_config_from_file(directory, config_file)
+    # Read the default configuration. Depending on which exists
+    config = load_config_from_file(directory, config_toml)
 
+    # Fallback certain values depending on the [project.name]
+    if project_name := pyproject_config.get("project", {}).get("name", ""):
+        # Fallback to the project name for the configuration name
+        # and the configuration package entries.
+        if not config.package:
+            config.package = project_name
+        if not config.name:
+            config.name = config.package
 
-def load_config_from_file(directory: str, config_file: str) -> Config:
+    return config
+
+
+def load_toml_from_file(config_file: str) -> Mapping[str, Any]:
     with open(config_file, "rb") as conffile:
-        config = tomllib.load(conffile)
+        return tomllib.load(conffile)
+
+
+def load_config_from_file(directory: str, config_file: str) -> Config:
+    config = load_toml_from_file(config_file)
 
     return parse_toml(directory, config)
 
@@ -141,10 +166,7 @@ def load_config_from_file(directory: str, config_file: str) -> Config:
 
 
 def parse_toml(base_path: str, config: Mapping[str, Any]) -> Config:
-    if "towncrier" not in (config.get("tool") or {}):
-        raise ConfigError("No [tool.towncrier] section.", failing_option="all")
-
-    config = config["tool"]["towncrier"]
+    config = config.get("tool", {}).get("towncrier", {})
     parsed_data = {}
 
     # Check for misspelt options.

src/towncrier/newsfragments/687.feature.rst

@@ -0,0 +1,3 @@
+When used with an `pyproject.toml` file, when no explicit values are
+defined for [tool.towncrier.name|package] they will now fallback to
+the value of [project.name].

src/towncrier/test/test_settings.py

@@ -3,6 +3,8 @@
 
 import os
 
+from textwrap import dedent
+
 from click.testing import CliRunner
 from twisted.trial.unittest import TestCase
 
@@ -112,22 +114,6 @@ def test_template_extended(self):
 
         self.assertEqual(config.template, ("towncrier.templates", "default.rst"))
 
-    def test_missing(self):
-        """
-        If the config file doesn't have the correct toml key, we error.
-        """
-        project_dir = self.mktemp_project(
-            pyproject_toml="""
-                [something.else]
-                blah='baz'
-            """
-        )
-
-        with self.assertRaises(ConfigError) as e:
-            load_config(project_dir)
-
-        self.assertEqual(e.exception.failing_option, "all")
-
     def test_incorrect_single_file(self):
         """
         single_file must be a bool.
@@ -194,6 +180,93 @@ def test_towncrier_toml_preferred(self):
         config = load_config(project_dir)
         self.assertEqual(config.package, "a")
 
+    def test_pyproject_only_pyproject_toml(self):
+        """
+        Towncrier will fallback to the [project.name] value in pyproject.toml.
+
+        This tests asserts that the minimal configuration is to do *nothing*
+        when using a pyproject.toml file.
+        """
+        project_dir = self.mktemp_project(
+            pyproject_toml="""
+                [project]
+                name = "a"
+            """,
+        )
+
+        config = load_config(project_dir)
+        self.assertEqual(config.package, "a")
+        self.assertEqual(config.name, "a")
+
+    def test_pyproject_assert_fallback(self):
+        """
+        This test is an extensive test of the fallback scenarios
+        for the `package` and `name` keys in the towncrier section.
+
+        It will fallback to pyproject.toml:name in any case.
+        And as such it checks the various fallback mechanisms
+        if the fields are not present in the towncrier.toml, nor
+        in the pyproject.toml files.
+
+        This both tests when things are *only* in the pyproject.toml
+        and default usage of the data in the towncrier.toml file.
+        """
+        pyproject_toml = dedent(
+            """
+        [project]
+        name = "foo"
+        [tool.towncrier]
+        """
+        )
+        towncrier_toml = dedent(
+            """
+        [tool.towncrier]
+        """
+        )
+        tests = [
+            "",
+            "name = '{name}'",
+            "package = '{package}'",
+            "name = '{name}'",
+            "package = '{package}'",
+        ]
+
+        def factory(name, package):
+            def func(test):
+                return dedent(test).format(name=name, package=package)
+
+            return func
+
+        for pp_fields in map(factory(name="a", package="b"), tests):
+            pp_toml = pyproject_toml + pp_fields
+            for tc_fields in map(factory(name="c", package="d"), tests):
+                tc_toml = towncrier_toml + tc_fields
+
+                # Create the temporary project
+                project_dir = self.mktemp_project(
+                    pyproject_toml=pp_toml,
+                    towncrier_toml=tc_toml,
+                )
+
+                # Read the configuration file.
+                config = load_config(project_dir)
+
+                # Now the values depend on where the fallback
+                # is.
+                # If something is in towncrier.toml, it will be preferred
+                # name fallsback to package
+                if "package" in tc_fields:
+                    package = "d"
+                else:
+                    package = "foo"
+                self.assertEqual(config.package, package)
+
+                if "name" in tc_fields:
+                    self.assertEqual(config.name, "c")
+                else:
+                    # fall-back to package name
+                    self.assertEqual(config.name, package)
+
     @with_isolated_runner
     def test_load_no_config(self, runner: CliRunner):
         """