bug#56362: CC Mode 5.35.1 (C++//l); Highlight for C++20 keywords

Hello again, Zhiwei.

I've now committed the changes to standalone CC Mode and the Emacs
master branch.

As a matter of interest, I've also committed support for C++20 concepts
and modules.

I'm closing the bug with this post.

-- 
Alan Mackenzie (Nuremberg, Germany).


On Wed, Sep 07, 2022 at 13:01:24 +0000, Alan Mackenzie wrote:
> Hello, Zhiwei.

> First of all, sorry that it's taken me two months to reply.

> Secondly, thanks for taking the trouble to submit this bug.  I have fixed
> the problems, partly, but I still have a lot of work to do to bring CC
> Mode up to the C++20 standard.  In particular, "concepts" and "requires"
> will need a lot doing.  I hope to do this work in the coming weeks.

> I have included a patch for these problems below; could you please test
> this patch on your CC Mode and your real C++ source files, and let me
> know how it goes.  As I said, it is not perfect, but it should be better
> than it was.  If you want any help with the patching or byte compiling of
> CC Mode, feel free to send me private email.

> For the problems you raised:

> On Sun, Jul 03, 2022 at 03:12:28 +0800, Zhiwei Chen wrote:
> > Package: cc-mode

> > See the comments.

> > #+begin_src C++
> > #if __has_include(<bits/stdc++.h>)
> > #include <bits/stdc++.h>
> > #endif

> > #include <cstdint>
> > #include <concepts>

> > // no highlight for consteval keyword
> > consteval int sqr(int x) {
> >     return x * x;
> > }

> Now fixed.

> > // no highlight for constinit keyword
> > constinit int four = sqr(16);

> Now fixed.

> > class Foo {
> > public:
> >     // <=> highlights wrong
> >     auto operator<=>(const Foo&) const = default;

> Now fixed.

> > private:
> >     // no highlight for alignas keyword
> >     alignas(alignof(std::uint64_t)) int val_;
> > };

> Now fixed.  It's also worth noting that "alignas" in a struct/class:

>     class alignas(64) Foo { ..... }

> should now fontify correctly.

> > template <typename T>
> > requires std::integral<T> // 'requires' occasionally has a font-lock-type-face
> > T add(T a, T b) {
> >     return a + b;
> > }

> Here's where I still need to make "requires" work properly.  I've
> temporarily make "requires" and "concept" C++ keywords, but in the above
> piece of code, "T add(T a, T b) {" is not correctly fontified.  But
> "requires" should now always be fontified as a keyword.

> > int main() {
> >     const char8_t c1 = 0; // char8_t is missing in `c-primitive-type-kwds'. cc-langs.el L2205

> >     return 0;
> > }
> > #+end_src

> char8_t is now in c-primitive-type-kwds.

> > Emacs  : GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.34, cairo version 1.17.6)
> >  of 2022-07-02
> > Package: CC Mode 5.35.1 (C++//l)
> > Buffer Style: gnu
> > c-emacs-features: (pps-extended-state col-0-paren posix-char-classes gen-string-delim gen-comment-delim syntax-properties 1-bit)

> [ CC Mode configuration appreciated, but snipped ]

> Here's the patch:



> diff -r 87af98f62eec cc-langs.el
> --- a/cc-langs.el	Wed Aug 31 18:28:12 2022 +0000
> +++ b/cc-langs.el	Wed Sep 07 12:38:20 2022 +0000
> @@ -1301,6 +1301,10 @@
>  		  ,@(when (c-major-mode-is 'java-mode)
>  		      '(">>>")))
 
> +      ;; The C++ "spaceship" operator.
> +      ,@(when (c-major-mode-is 'c++-mode)
> +	  `((left-assoc "<=>")))
> +
>        ;; Relational.
>        (left-assoc "<" ">" "<=" ">="
>  		  ,@(when (c-major-mode-is 'java-mode)
> @@ -1414,7 +1418,7 @@
>  	 "^" "??'" "xor" "&" "bitand" "|" "??!" "bitor" "~" "??-" "compl"
>  	 "!" "=" "<" ">" "+=" "-=" "*=" "/=" "%=" "^="
>  	 "??'=" "xor_eq" "&=" "and_eq" "|=" "??!=" "or_eq"
> -	 "<<" ">>" ">>=" "<<=" "==" "!=" "not_eq" "<=" ">="
> +	 "<<" ">>" ">>=" "<<=" "==" "!=" "not_eq" "<=>" "<=" ">="
>  	 "&&" "and" "||" "??!??!" "or" "++" "--" "," "->*" "->"
>  	 "()" "[]" "<::>" "??(??)")
>    ;; These work like identifiers in Pike.
> @@ -1535,8 +1539,10 @@
>    "List of all arithmetic operators, including \"+=\", etc."
>    ;; Note: in the following, there are too many operators for AWK and IDL.
>    t (append (c-lang-const c-assignment-operators)
> -	    '("+" "-" "*" "/" "%"
> +	    `("+" "-" "*" "/" "%"
>  	      "<<" ">>"
> +	      ,@(if (c-major-mode-is 'c++-mode)
> +		    '("<=>"))
>  	      "<" ">" "<=" ">="
>  	      "==" "!="
>  	      "&" "^" "|"
> @@ -2187,7 +2193,7 @@
>  	'("_Bool" "_Complex" "_Imaginary") ; Conditionally defined in C99.
>  	(c-lang-const c-primitive-type-kwds))
>    c++  (append
> -	'("bool" "wchar_t" "char16_t" "char32_t")
> +	'("bool" "wchar_t" "char8_t" "char16_t" "char32_t")
>  	(c-lang-const c-primitive-type-kwds))
>    ;; Objective-C extends C, but probably not the new stuff in C99.
>    objc (append
> @@ -2580,8 +2586,8 @@
>    t    nil
>    (c c++) '("extern" "inline" "register" "static")
>    c    (append '("auto") (c-lang-const c-modifier-kwds))
> -  c++  (append '("constexpr" "explicit" "friend" "mutable" "template"
> -		 "thread_local" "virtual")
> +  c++  (append '("consteval" "constexpr" "constinit" "explicit" "friend"
> +		 "mutable" "template" "thread_local" "virtual")
>  	       ;; "using" is now handled specially (2020-09-14).
>  	       (c-lang-const c-modifier-kwds))
>    objc '("auto" "bycopy" "byref" "extern" "in" "inout" "oneway" "out" "static")
> @@ -2655,7 +2661,8 @@
>    (c c++) '(;; GCC extension.
>  	    "__attribute__"
>  	    ;; MSVC extension.
> -	    "__declspec"))
> +	    "__declspec")
> +  c++ (append (c-lang-const c-decl-hangon-kwds) '("alignas")))
 
>  (c-lang-defconst c-decl-hangon-key
>    ;; Adorned regexp matching `c-decl-hangon-kwds'.
> @@ -2880,7 +2887,7 @@
>  	    "__attribute__"
>  	    ;; MSVC extension.
>  	    "__declspec")
> -  c++ (append (c-lang-const c-paren-nontype-kwds) '("noexcept")))
> +  c++ (append (c-lang-const c-paren-nontype-kwds) '("noexcept" "alignas")))
 
>  (c-lang-defconst c-paren-nontype-key
>    t (c-make-keywords-re t (c-lang-const c-paren-nontype-kwds)))
> @@ -3256,11 +3263,17 @@
>  (c-lang-defconst c-keywords
>    ;; All keywords as a list.
>    t (c--delete-duplicates
> -     (c-lang-defconst-eval-immediately
> -      `(append ,@(mapcar (lambda (kwds-lang-const)
> -			   `(c-lang-const ,kwds-lang-const))
> -			 c-kwds-lang-consts)
> -	       nil))
> +     (append				; Temporary, 2022-09-07
> +      (c-lang-defconst-eval-immediately
> +       `(append ,@(mapcar (lambda (kwds-lang-const)
> +			    `(c-lang-const ,kwds-lang-const))
> +			  c-kwds-lang-consts)
> +		nil))
> +      ;; Temporary addition for C++ until concepts have been worked out properly.
> +      ;; 2022-09-07.
> +      `(,@(if (c-major-mode-is 'c++-mode)
> +	      '("concept" "requires")))
> +      nil)
>       :test 'string-equal))
 
>  (c-lang-defconst c-keywords-regexp


> -- 
> Alan Mackenzie (Nuremberg, Germany).