[rr-]

Google Raises: sections written without the Type: text form made parse() raise ParseError:

>>> parse("Short.\n\nRaises:\n    ValueError\n", "google")
ParseError: Expected a colon in 'ValueError'.
>>> parse("Short.\n\nRaises:\n    Something may go wrong if the input\n    is not what we expect.\n", "google")
ParseError: Expected a colon in 'Something may go wrong if the input'.

Now:

• A type alone on its line is a raises with that type and no description. Several types work too (KeyError, TypeError, os.error or IOError), as do Sphinx-marked ones (~pkg.Error). A description indented below the type belongs to it, as Numpydoc writes it.
• A section in which no item starts with a type is one raises with no type, holding the prose. A sentence with a colon in it (If the input is bad: a ValueError.) counts as prose, because the text before its colon has spaces.
• Mixed sections work item by item: ValueError: Bad. then TypeError gives two raises.
• : text, with nothing before the colon, gives a raises with no type instead of type_name=''.

Compose writes a type with no description without the colon, and a lone raises with no type as its prose, so both read back the same. A raises with no type among typed ones still composes as : text.

Parity against main: 381 of 29,127 docstrings differ, and every one is about raises.

• Docstrings with a Google raises section (Raises:, Exceptions:, Except:): 6 case inputs, 1 stdlib and 263 generated. 163 of them used to raise ParseError in parse google and now parse, including the real google-auth docstring OnDemandCredentials.refresh. Some others had garbage types like - TypeError from a bullet list, which is now one raises holding the list. In auto mode these can now pick Google, as for OnDemandCredentials.refresh and the stdlib ssl module docstring, whose Exceptions: section now reads as one typeless raises.
• The other 3 case inputs and 108 generated docstrings differ only when composed as Google: a raises with a type and no description loses its trailing colon, and a lone typeless raises is written as prose.

Bench on 3.8: parse 0.99–1.01x of main, compose google 1.01–1.02x.