Missing support for GNU extension types like `_Complex` or `_Fract`

[marxin]

I'm currently working on the transition of the GNU C compiler (GCC) manuals and I noticed there are unsupported C extensions like:

.. c:function:: complex long foo(int)
.. c:function:: _Complex long foo(int)
.. c:function:: long fract __satfractunssisq (unsigned int a)

  My function.

where I see the following parsing error:

/home/marxin/Programming/texi2rst-generated/sphinx/demo/demo.rst:66: WARNING: Invalid C declaration: Expected identifier, got user-defined keyword: complex. Remove it from c_extra_keywords to allow it as identifier.
Currently c_extra_keywords is ['alignas', 'alignof', 'bool', 'complex', 'imaginary', 'noreturn', 'static_assert', 'thread_local']. [error at 7]
  complex long foo(int)
  -------^
/home/marxin/Programming/texi2rst-generated/sphinx/demo/demo.rst:67: WARNING: Invalid C declaration: Expected identifier in nested name, got keyword: _Complex [error at 8]
  _Complex long foo(int)
  --------^
/home/marxin/Programming/texi2rst-generated/sphinx/demo/demo.rst:68: WARNING: Error in declarator or parameters
Invalid C declaration: Expecting "(" in parameters. [error at 11]
  long fract __satfractunssisq (unsigned int a)
  -----------^

Right now, there's some special casing for e.g. 'unsigned' type:

sphinx/sphinx/domains/c.py

Lines 2566 to 2585 in 6ac326e

	elements = []
	if self.skip_word_and_ws('signed'):
	elements.append('signed')
	elif self.skip_word_and_ws('unsigned'):
	elements.append('unsigned')
	while 1:
	if self.skip_word_and_ws('short'):
	elements.append('short')
	elif self.skip_word_and_ws('long'):
	elements.append('long')
	else:
	break
	if self.skip_word_and_ws('char'):
	elements.append('char')
	elif self.skip_word_and_ws('int'):
	elements.append('int')
	elif self.skip_word_and_ws('double'):
	elements.append('double')
	elif self.skip_word_and_ws('__int64'):
	elements.append('__int64')

One possible fix is adding the mentioned C extension handling for the following types:
https://gcc.gnu.org/onlinedocs/gcc/Fixed-Point.html
https://gcc.gnu.org/onlinedocs/gcc/Complex.html

or I can see a domain parser can become public via an API entry point:

sphinx/sphinx/domains/c.py

Lines 2128 to 2131 in 6ac326e

	_simple_fundamental_types = (
	'void', '_Bool', 'bool', 'char', 'int', 'float', 'double',
	'__int64',
	)

What do you think?

[marxin]

One related problem might be something like:

.. c:function:: unsigned HOST_WIDE_INT foo ()

Where we have defined HOST_WIDE_INT with a typedef to something like unsigned long. Can one handle it with Sphinx somehow?

[marxin]

@jakobandersen

[jakobandersen]

Good idea. I believe PR #9547 should contain a fully updated parsing of fundamental types and the fixed-point types.

[jakobandersen]

One related problem might be something like:

.. c:function:: unsigned HOST_WIDE_INT foo ()

Where we have defined HOST_WIDE_INT with a typedef to something like unsigned long. Can one handle it with Sphinx somehow?

Yes. If you treat HOST_WIDE_INT as a user-configurable fundamental type (component) then it would be formatted as such, which I'm not sure is a good idea (and it's currently not supported).
Instead, you can treat it as a user-configurable attribute: in conf.py add

c_id_attributes = ["HOST_WIDE_INT"]

That should work in the latest versions.

[marxin]

Good idea. I believe PR #9547 should contain a fully updated parsing of fundamental types and the fixed-point types.

Thanks for working on that. One comment I have is that the type parsing should be shared among c and cpp domains.

[marxin]

That should work in the latest versions.

I can confirm that approach works, thanks.

[marxin]

And one more example I noticed is unsupported by cpp domain:

.. cpp:function:: int gimple_build (int (*valueize) (int) = NULL)

  Just a fn.

resulting in the following error:

/home/marxin/Programming/texi2rst-generated/sphinx/demo/demo.rst:66: WARNING: Error when parsing function declaration.
If the function has no return type:
  Error in declarator or parameters-and-qualifiers
  Invalid C++ declaration: Expected identifier in nested name, got keyword: int [error at 3]
    int gimple_build (int (*valueize) (int) = NULL)
    ---^
If the function has a return type:
  Error in declarator or parameters-and-qualifiers
  If pointer to member declarator:
    Invalid C++ declaration: Expected '::' in pointer to member (function). [error at 17]
      int gimple_build (int (*valueize) (int) = NULL)
      -----------------^
  If declarator-id:
    Error in declarator
    If declarator-id with parameters-and-qualifiers:
      Invalid C++ declaration: Expected identifier in nested name. [error at 23]
        int gimple_build (int (*valueize) (int) = NULL)
        -----------------------^
    If parenthesis in noptr-declarator:
      Error in declarator
      If declarator-id with parameters-and-qualifiers:
        Invalid C++ declaration: Expected "0" or "delete" or "default" in initializer-specifier. [error at 42]
          int gimple_build (int (*valueize) (int) = NULL)
          ------------------------------------------^
      If parenthesis in noptr-declarator:
        Invalid C++ declaration: Expected ')' in "( ptr-declarator )" [error at 35]
          int gimple_build (int (*valueize) (int) = NULL)
          -----------------------------------^

[jakobandersen]

Good idea. I believe PR #9547 should contain a fully updated parsing of fundamental types and the fixed-point types.

Thanks for working on that. One comment I have is that the type parsing should be shared among c and cpp domains.

Right, I suspected that but didn't work on it yet as it requires mangling to generate stable IDs. Are the fixed-point types supported in C++ mode? I couldn't get it to compile.

[marxin]

Are the fixed-point types supported in C++ mode?

No, it's only C extension.