fix: require version in dynamic if unset

Signed-off-by: Henry Schreiner <[email protected]>

pyproject_metadata/__init__.py

@@ -196,7 +196,6 @@ class StandardMetadata:
 
     def __post_init__(self) -> None:
         self.name = re.sub(r'[-_.]+', '-', self.name).lower()
-        self._update_dynamic(self.version)
 
     @classmethod
     def from_pyproject(
@@ -226,6 +225,10 @@ def from_pyproject(
 
         version_string = fetcher.get_str('project.version')
         requires_python_string = fetcher.get_str('project.requires-python')
+        version = packaging.version.Version(version_string) if version_string else None
+
+        if version is None and 'version' not in dynamic:
+            raise ConfigurationError('Field "project.version" missing and "version" not specified in "project.dynamic"')
 
         # Description can't be multiline
         description = fetcher.get_str('project.description')
@@ -234,7 +237,7 @@ def from_pyproject(
 
         return cls(
             name,
-            packaging.version.Version(version_string) if version_string else None,
+            version,
             description,
             cls._get_license(fetcher, project_dir),
             cls._get_readme(fetcher, project_dir),
@@ -255,8 +258,6 @@ def from_pyproject(
     def _update_dynamic(self, value: Any) -> None:
         if value and 'version' in self.dynamic:
             self.dynamic.remove('version')
-        elif not value and 'version' not in self.dynamic:
-            self.dynamic.append('version')
 
     def __setattr__(self, name: str, value: Any) -> None:
         # update dynamic when version is set