Provide support for C functional macros

[Slabity]

Currently, cexpr cannot produce values that use functional macros to calculate. It would be very useful if cexpr supported them.

[jethrogb]

cexpr support is almost trivial, assuming these functional macros evaluate into proper expressions. If this is useful I can implement it. Note however that you must indicate to cexpr whether you'd be parsing a functional macro or a regular macro, because there is no way to distinguish between the two at the token level.

[Slabity]

there is no way to distinguish between the two at the token level.

How so?

[jethrogb]

Both of

m(a) -1
m (a) -1

are

[
  Identifier("m"),
  Punctuation("("),
  Identifier("a"),
  Punctuation(")"),
  Punctuation("-"),
  Literal("1")
]

[Slabity]

Could there be a Whitespace token to differentiate the two?

[jethrogb]

Possibly. But you need a lexer that generates those tokens. Clang does not.

[emilio]

Hi, @jethrogb, would it be fine to give you a boolean that tells whether the current macro definition is function-like?

Clang has an API for that (clang_Cursor_isMacroFunctionLike), and it'd solve some bindgen issues like rust-lang/rust-bindgen#753

[jethrogb]

Yes that would work. cexpr just needs to know whether it's parsing a functional or regular macro. I can probably look at this on Sunday.

Note: clang_Cursor_isMacroFunctionLike was introduced relatively recently and is e.g. not available on Ubuntu 16.04.

Also notably, clang_Cursor_Evaluate was introduced in the same commit, but I think it's not as powerful as cexpr.

[emilio]

Right both are libclang 3.9+. But nicely enough bindgen loads libclang at runtime so can detect which functions are available, so it'd be nice to start using them when available.

[nicokoch]

Any update on this? :)

[jethrogb]

It was too hot to do any work ;) Next weekend... Or feel free to pick it up yourself before then.

[Slabity]

@jethrogb Any update?

[jethrogb]

Was going to do this this morning, but got distracted by 0ea1367 and 4fdd26b

[jethrogb]

Parsing functional macro declarations is now supported in fe05507.

I suppose you'd also like to evaluate them if they're used as part of a another macro definition? Because of token-pasting, stringizing and non-reentrant evaluation, that's not super easy. Reference: https://www.mirbsd.org/htman/i386/manINFO/cppinternals.html
http://port70.net/~nsz/c/c89/c89-draft.html#3.8.3
https://superb-dca2.dl.sourceforge.net/project/mcpp/mcpp/V.2.7.2/mcpp-summary-272.pdf
http://c0x.coding-guidelines.com/6.10.3.pdf
http://c0x.coding-guidelines.com/6.10.3.1.pdf