fix: better error messages based on feedback

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

cibuildwheel/options.py

@@ -551,6 +551,8 @@ def get(
 
 
 class Options:
+    pyproject_toml: dict[str, Any] | None
+
     def __init__(
         self,
         platform: PlatformName,
@@ -574,7 +576,7 @@ def __init__(
             with self.package_dir.joinpath("pyproject.toml").open("rb") as f:
                 self.pyproject_toml = tomllib.load(f)
         except FileNotFoundError:
-            self.pyproject_toml = {}
+            self.pyproject_toml = None
 
     @property
     def config_file_path(self) -> Path | None:

cibuildwheel/projectfiles.py

@@ -85,12 +85,12 @@ def setup_py_python_requires(content: str) -> str | None:
         return None
 
 
-def get_requires_python_str(package_dir: Path, pyproject_toml: dict[str, Any]) -> str | None:
+def get_requires_python_str(package_dir: Path, pyproject_toml: dict[str, Any] | None) -> str | None:
     """Return the python requires string from the most canonical source available, or None"""
 
     # Read in from pyproject.toml:project.requires-python
     with contextlib.suppress(KeyError, IndexError, TypeError):
-        return str(pyproject_toml["project"]["requires-python"])
+        return str((pyproject_toml or {})["project"]["requires-python"])
 
     # Read in from setup.cfg:options.python_requires
     config = configparser.ConfigParser()
@@ -106,18 +106,24 @@ def get_requires_python_str(package_dir: Path, pyproject_toml: dict[str, Any]) -
     return None
 
 
-def resolve_dependency_groups(pyproject_toml: dict[str, Any], *groups: str) -> tuple[str, ...]:
+def resolve_dependency_groups(
+    pyproject_toml: dict[str, Any] | None, *groups: str
+) -> tuple[str, ...]:
     """
     Get the packages in dependency-groups for a package.
     """
 
     if not groups:
         return ()
 
+    if pyproject_toml is None:
+        msg = f"Didn't find a pyproject.toml, so can't read [dependency-groups] {groups!r} from it!"
+        raise FileNotFoundError(msg)
+
     try:
         dependency_groups_toml = pyproject_toml["dependency-groups"]
     except KeyError:
-        msg = f"Didn't find [dependency-groups], which are needed to resolve {groups!r}."
+        msg = f"Didn't find [dependency-groups] in pyproject.toml, which is needed to resolve {groups!r}."
         raise KeyError(msg) from None
 
     return dependency_groups.resolve(dependency_groups_toml, *groups)

unit_test/projectfiles_test.py

@@ -2,6 +2,8 @@
 
 from textwrap import dedent
 
+import pytest
+
 from cibuildwheel._compat import tomllib
 from cibuildwheel.projectfiles import (
     get_requires_python_str,
@@ -264,3 +266,13 @@ def test_read_dep_groups():
     assert resolve_dependency_groups(pyproject_toml, "group1") == ("pkg1", "pkg2")
     assert resolve_dependency_groups(pyproject_toml, "group2") == ("pkg3",)
     assert resolve_dependency_groups(pyproject_toml, "group1", "group2") == ("pkg1", "pkg2", "pkg3")
+
+
+def test_dep_group_no_file_error():
+    with pytest.raises(FileNotFoundError, match="pyproject.toml"):
+        resolve_dependency_groups(None, "test")
+
+
+def test_dep_group_no_section_error():
+    with pytest.raises(KeyError, match="pyproject.toml"):
+        resolve_dependency_groups({}, "test")