bug#57318: 29.0.50; c++-mode: Functions are shown as variables: partial template specialization

bug#57318: 29.0.50; c++-mode: Functions are shown as variables: partial template specialization

[Naofumi Yasufuku]

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Hello,

In the case of C++ partial template specialization [1], functions are
shown as variables.  Please look at the attached screenshots.

  1. emacs -Q
  2. open attached C++ code "specialization.cc"

  attachments:
  - NG_cc-partial-specialization.png
  - OK_cc-partial-specialization.png
  - specialization.cc

In cc-engine.el c-do-declarators, given CDD-NOT-TOP is non-nil at blow:

-------------------------------------------------------------
(defun c-do-declarators
    (cdd-limit cdd-list cdd-not-top cdd-comma-prop cdd-function)

[..snip..]

    (while
	(and (not cdd-exhausted)
	     (setq cdd-decl-res (c-forward-declarator cdd-limit)))
      (setq cdd-next-pos (point)
	    cdd-id-start (car cdd-decl-res)
	    cdd-id-end (cadr cdd-decl-res)
	    cdd-got-func (and (eq (char-after) ?\()
			  (or (not (c-major-mode-is 'c++-mode))
			      (not cdd-not-top)  <<<< nil if "class foo<T, ..>"
			      (car (cddr (cddr cdd-decl-res))) ; Id is in
					; parens, etc.
			      (save-excursion
				(forward-char)
				(c-forward-syntactic-ws)
				(looking-at "[*&]")))
-------------------------------------------------------------

-------------------------------------------------------------
template<>>
class One<char> {
public:
    One() {}    // (not cdd-not-top): t
private:
    char _c;
};

template<typename T>
class Two<T, char> {    // "," in "class A<...>"
public:
    Two() {}    // (not cdd-not-top): nil
private:
    T _t;
    char _c;
};
-------------------------------------------------------------

After a brief investigation, the attached cc-engine.el patch seems to
solve this issue at least, but it is not tested enough.

  attachments:
  - 0001-cc-mode-Fix-function-fontification-in-the-case-of-C-.patch


[1] https://en.cppreference.com/w/cpp/language/partial_specialization
-------------------------------------------------------------
$ g++ -o specialization specialization.cc
$ ./specialization
One<T>: primary
One<char>: specialization
Two<T1, T2>: primary
Two<T, char>: specialization
Two<T, T*>: specialization
Two<T, T&>: specialization
Two<T, T[]>: specialization
Two<char, char*>: specialization
Two<char, char&>: specialization
Two<char, char[]>: specialization
$
-------------------------------------------------------------

Regards,
  Naofumi


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#include <iostream>

template<typename T>
class One {
public:
    One() {}
    ~One() {}
    void fn() { std::cout << "One<T>: primary" << std::endl; }
private:
    T _t;
};

template<>
class One<char> {
public:
    One() {}
    ~One() {}
    void fn() { std::cout << "One<char>: specialization" << std::endl; }
private:
    char _c;
};

template<typename T1, typename T2>
class Two {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T1, T2>: primary" << std::endl; }
private:
    T1 _t1;
    T2 _t2;
};

template<typename T>
class Two<T, char> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T, char>: specialization" << std::endl; }
private:
    T _t;
    char _c;
};

template<typename T>
class Two<T, T*> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T, T*>: specialization" << std::endl; }
private:
    T _t;
    T* _pt;
};

template<typename T>
class Two<T, T&> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T, T&>: specialization" << std::endl; }
private:
    T _t;
};

template<typename T>
class Two<T, T[]> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T, T[]>: specialization" << std::endl; }
private:
    T _t;
};

template<>
class Two<char, char*> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<char, char*>: specialization" << std::endl; }
private:
    char _c;
};

template<>
class Two<char, char&> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<char, char&>: specialization" << std::endl; }
private:
    char _c;
};

template<>
class Two<char, char[]> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<char, char[]>: specialization" << std::endl; }
private:
    char _c;
};

int main() {
    One<int> oneInt; oneInt.fn();
    One<char> oneChar; oneChar.fn();

    Two<int, int> twoIntInt;  twoIntInt.fn();
    Two<int, char> twoIntChar; twoIntChar.fn();

    Two<int, int*> twoIntIntP; twoIntIntP.fn();
    Two<int, int&> twoIntIntR; twoIntIntR.fn();
    Two<int, int[]> twoIntIntA; twoIntIntA.fn();

    Two<char, char*> twoCharCharP; twoCharCharP.fn();
    Two<char, char&> twoCharCharR; twoCharCharR.fn();
    Two<char, char[]> twoCharCharA; twoCharCharA.fn();

    return 0;
}

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From f8c2d7c8d562f92ab9d8eb22a8f661f5ceb6e39c Mon Sep 17 00:00:00 2001
From: Naofumi Yasufuku <naofumi@yasufuku.dev>
Date: Sun, 21 Aug 2022 21:06:13 +0900
Subject: [PATCH] cc-mode: Fix function fontification in the case of C++
 partial specialization

* lisp/progmodes/cc-engine.el (c-update-brace-stack): Skip "," and "*"
found in "class foo : bar, ..." (base-clause of a class) or
"class foo<T, T*, T&, T[], ...>" (partial template specialization).
---
 lisp/progmodes/cc-engine.el | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index bc6155dd66..f5d81cb530 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -6141,13 +6141,16 @@ c-update-brace-stack
 		(c-forward-<>-arglist nil)) ; Should always work.
 	      (when (> (point) to)
 		(setq bound-<> (point)))
-	    (forward-char)))
+	    (forward-char))
+	  (if (and s
+		   (eq (car s) 0))
+	      (setq s (cons -1 (cdr s))))) ; for "class foo<T, T*, T&, T[] ...>"
 	 ((and (equal match ":")
 	       s
 	       (eq (car s) 0))
-	  (setq s (cons -1 (cdr s))))
-	 ((and (equal match ",")
-	       (eq (car s) -1)))	; at "," in "class foo : bar, ..."
+	  (setq s (cons -1 (cdr s)))) ; for "," in "class foo : bar, ..."
+	 ((and (member match '("*" ","))
+	       (eq (car s) -1))) ; in "class foo : ..." or "class foo<...>"
 	 ((member match '(";" "*" "," ")"))
 	  (when (and s (cdr s) (<= (car s) 0))
 	    (setq s (cdr s))))
-- 
2.37.2


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bug#57318: 29.0.50; c++-mode: Functions are shown as variables: partial template specialization

[Naofumi Yasufuku]

[-- Attachment #1: Type: text/plain, Size: 1682 bytes --]

Naofumi Yasufuku <naofumi@yasufuku.dev> writes:

> Hello,
>
> In the case of C++ partial template specialization [1], functions are
> shown as variables.  Please look at the attached screenshots.
>
>   1. emacs -Q
>   2. open attached C++ code "specialization.cc"
>
>   attachments:
>   - NG_cc-partial-specialization.png
>   - OK_cc-partial-specialization.png
>   - specialization.cc
>
[..snip..]
>
> After a brief investigation, the attached cc-engine.el patch seems to
> solve this issue at least, but it is not tested enough.
>
>   attachments:
>   - 0001-cc-mode-Fix-function-fontification-in-the-case-of-C-.patch
>

Previous patch still has a problem with sizeof() specializations.
Updated patch and screenshots are attached.

  attachments:
  - 0001-cc-mode-Fix-function-fontification-in-the-case-of-C-v2.patch
  - NG_cc-partial-specialization-v1.png
  - OK_cc-partial-specialization-v2.png
  - specialization.cc

-------------------------------------------------------------
template<typename T1, size_t>
class TwoSz {
public:
    TwoSz() {}
private:
    T1 _t1;
};

template<typename T>
class TwoSz<T, sizeof(int)> {
public:
    TwoSz() {}
private:
    T _t1;
};
-------------------------------------------------------------
$ ./specialization
One<T>: primary
One<char>: specialization
Two<T1, T2>: primary
Two<T, char>: specialization
Two<T, T*>: specialization
Two<T, T&>: specialization
Two<T, T[]>: specialization
Two<char, char*>: specialization
Two<char, char&>: specialization
Two<char, char[]>: specialization
TwoSz<T1, size_t>: primary
TwoSz<T, sizeof(int)>: specialization
$
-------------------------------------------------------------

Best regards,
  Naofumi


[-- Attachment #2: sizeof problem --]
[-- Type: image/png, Size: 638081 bytes --]

[-- Attachment #3: ok with patch v2 --]
[-- Type: image/png, Size: 637252 bytes --]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #4: patch v2 --]
[-- Type: text/x-patch, Size: 1534 bytes --]

From fc88895a0daa9f43c789650ac7f0438cd2466811 Mon Sep 17 00:00:00 2001
From: Naofumi Yasufuku <naofumi@yasufuku.dev>
Date: Sun, 28 Aug 2022 13:33:01 +0900
Subject: [PATCH] cc-mode: Fix function fontification in the case of C++
 partial specialization

* lisp/progmodes/cc-engine.el (c-update-brace-stack): Skip "*", ",",
and ")" found in "class foo : bar, .." (base-clause of a class) or
"class foo<T, T*, T&, T[], sizeof(..), ..>" (partial template specialization)
(bug#57318).
---
 lisp/progmodes/cc-engine.el | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index b2d1f15d39..5d1a11e9e8 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -6141,13 +6141,18 @@ c-update-brace-stack
 		(c-forward-<>-arglist nil)) ; Should always work.
 	      (when (> (point) to)
 		(setq bound-<> (point)))
-	    (forward-char)))
+	    (forward-char))
+	  (if (and s
+		   (eq (car s) 0))
+	      ;; for "class foo<T, T*, T&, T[], sizeof(..), ..>"
+	      (setq s (cons -1 (cdr s)))))
 	 ((and (equal match ":")
 	       s
 	       (eq (car s) 0))
+	  ;; for "," in "class foo : bar, .."
 	  (setq s (cons -1 (cdr s))))
-	 ((and (equal match ",")
-	       (eq (car s) -1)))	; at "," in "class foo : bar, ..."
+	 ((and (eq (car s) -1) ; in "class foo : .." or "class foo<..>"
+	       (member match '("*" "," ")"))))
 	 ((member match '(";" "*" "," ")"))
 	  (when (and s (cdr s) (<= (car s) 0))
 	    (setq s (cdr s))))
-- 
2.37.2


[-- Attachment #5: test c++ source --]
[-- Type: text/plain, Size: 2970 bytes --]

#include <iostream>

template<typename T>
class One {
public:
    One() {}
    ~One() {}
    void fn() { std::cout << "One<T>: primary" << std::endl; }
private:
    T _t;
};

template<>
class One<char> {
public:
    One() {}
    ~One() {}
    void fn() { std::cout << "One<char>: specialization" << std::endl; }
private:
    char _c;
};

template<typename T1, typename T2>
class Two {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T1, T2>: primary" << std::endl; }
private:
    T1 _t1;
    T2 _t2;
};

template<typename T>
class Two<T, char> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T, char>: specialization" << std::endl; }
private:
    T _t;
    char _c;
};

template<typename T>
class Two<T, T*> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T, T*>: specialization" << std::endl; }
private:
    T _t;
    T* _pt;
};

template<typename T>
class Two<T, T&> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T, T&>: specialization" << std::endl; }
private:
    T _t;
};

template<typename T>
class Two<T, T[]> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<T, T[]>: specialization" << std::endl; }
private:
    T _t;
};

template<>
class Two<char, char*> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<char, char*>: specialization" << std::endl; }
private:
    char _c;
};

template<>
class Two<char, char&> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<char, char&>: specialization" << std::endl; }
private:
    char _c;
};

template<>
class Two<char, char[]> {
public:
    Two() {}
    ~Two() {}
    void fn() { std::cout << "Two<char, char[]>: specialization" << std::endl; }
private:
    char _c;
};

template<typename T1, size_t>
class TwoSz {
public:
    TwoSz() {}
    ~TwoSz() {}
    void fn() { std::cout << "TwoSz<T1, size_t>: primary" << std::endl; }
private:
    T1 _t1;
};

template<typename T>
class TwoSz<T, sizeof(int)> {
public:
    TwoSz() {}
    ~TwoSz() {}
    void fn() { std::cout << "TwoSz<T, sizeof(int)>: specialization" << std::endl; }
private:
    T _t1;
};

class Base1 {};
template<typename T1, size_t> class Base2 {};
template<typename T> class Derived : public Base1, Base2<T, sizeof(int)> {
public:
  Derived() {}
};

int main() {
    One<int> oneInt; oneInt.fn();
    One<char> oneChar; oneChar.fn();

    Two<int, int> twoIntInt;  twoIntInt.fn();
    Two<int, char> twoIntChar; twoIntChar.fn();

    Two<int, int*> twoIntIntP; twoIntIntP.fn();
    Two<int, int&> twoIntIntR; twoIntIntR.fn();
    Two<int, int[]> twoIntIntA; twoIntIntA.fn();

    Two<char, char*> twoCharCharP; twoCharCharP.fn();
    Two<char, char&> twoCharCharR; twoCharCharR.fn();
    Two<char, char[]> twoCharCharA; twoCharCharA.fn();

    TwoSz<int, 8> twoSzInt8; twoSzInt8.fn();
    TwoSz<int, sizeof(int)> twoSzIntSizeofI; twoSzIntSizeofI.fn();

    Derived<int> derived{};

    return 0;
}

bug#57318: 29.0.50; c++-mode: Functions are shown as variables: partial template specialization

[Alan Mackenzie]

Hello, Naofumi.

Thank you indeed for your bug report, and thanks even more for
diagnosing the cause and writing a patch!

I'm truly astounded that you managed to debug this problem, hidden as it
was in the fontification parts of CC Mode, which are difficult to run
with the debugger.  Respect!

Looking at your patch, I can see one or two problems with it.  The main
one is that after encountering a template opener "<", I'm a bit worried
about the accuracy of checking for the matching ">".

Looking further into the problem, it seems the misfontification bug was
triggered by the commas in the template expressions.  When there's a
comma there, the (c-forward-<>-arglist ...) call (which "; Should always
work") fails.  This failure is caused by the dynamic binding of
c-restricted-<>-arglists to t.

When this dynamic binding is instead at nil (rather than t), the
fontification works properly, with functions fontified as functions.
The reason for this faulty binding was fixing a bug report where
scrolling a buffer containing lots of templates was very slow.  Binding
c-restricted-<>-arglists to t "solved" that slowness.

That slowness had been caused by inefficient scanning of the template
structures.  I've now identified and implemented an alternative
optimisation, which doesn't cause problems with commas in templates.

So I must apologize that I won't be using your patch, but I thoroughly
appreciate the time you must have spent debugging the problem.

Can I ask you, please, to apply and test my proposed patch, which I
enclose below.  Would you please test it on your real C++ source code,
and either confirm it really works, or say what's still faulty about it.
If there are any problems with applying the patch, feel free to send me
personal email.



diff -r 8f28cf5aae11 cc-engine.el
--- a/cc-engine.el	Sat Aug 27 09:10:03 2022 +0000
+++ b/cc-engine.el	Tue Aug 30 19:46:56 2022 +0000
@@ -146,6 +146,11 @@
 ;;       Put on the brace which introduces a brace list and on the commas
 ;;       which separate the elements within it.
 ;;
+;; 'c-<>-c-types-set
+;;   This property is set on an opening angle bracket, and indicates that
+;;   any "," separators within the template/generic expression have been
+;;   marked with a 'c-type property value 'c-<>-arg-sep (see above).
+;;
 ;; 'c-awk-NL-prop
 ;;   Used in AWK mode to mark the various kinds of newlines.  See
 ;;   cc-awk.el.
@@ -6153,7 +6158,7 @@
 			(forward-char))))
 	  (backward-char)
 	  (if (let ((c-parse-and-markup-<>-arglists t)
-		    (c-restricted-<>-arglists t))
+		    c-restricted-<>-arglists)
 		(c-forward-<>-arglist nil)) ; Should always work.
 	      (when (> (point) to)
 		(setq bound-<> (point)))
@@ -8526,9 +8531,9 @@
 	arg-start-pos)
     ;; If the '<' has paren open syntax then we've marked it as an angle
     ;; bracket arglist before, so skip to the end.
-    (if (and (not c-parse-and-markup-<>-arglists)
-	     syntax-table-prop-on-<)
-
+    (if (and syntax-table-prop-on-<
+	     (or (not c-parse-and-markup-<>-arglists)
+		 (c-get-char-property (point) 'c-<>-c-types-set)))
 	(progn
 	  (forward-char)
 	  (if (and (c-go-up-list-forward)
@@ -8623,6 +8628,7 @@
 			       (c-unmark-<->-as-paren (point)))))
 		      (c-mark-<-as-paren start)
 		      (c-mark->-as-paren (1- (point)))
+		      (c-put-char-property start 'c-<>-c-types-set t)
 		      (c-truncate-lit-pos-cache start))
 		    (setq res t)
 		    nil))		; Exit the loop.
diff -r 8f28cf5aae11 cc-fonts.el
--- a/cc-fonts.el	Sat Aug 27 09:10:03 2022 +0000
+++ b/cc-fonts.el	Tue Aug 30 19:46:56 2022 +0000
@@ -937,17 +937,16 @@
     (save-excursion
       (let ((pos (point)))
 	(c-backward-syntactic-ws (max (- (point) 500) (point-min)))
-	(c-clear-char-properties
-	 (if (and (not (bobp))
-		  (memq (c-get-char-property (1- (point)) 'c-type)
-			'(c-decl-arg-start
-			  c-decl-end
-			  c-decl-id-start
-			  c-decl-type-start
-			  c-not-decl)))
-	     (1- (point))
-	   pos)
-	 limit 'c-type)))
+	(when (and (not (bobp))
+		   (memq (c-get-char-property (1- (point)) 'c-type)
+			 '(c-decl-arg-start
+			   c-decl-end
+			   c-decl-id-start
+			   c-decl-type-start
+			   c-not-decl)))
+	  (setq pos (1- (point))))
+	(c-clear-char-properties pos limit 'c-type)
+	(c-clear-char-properties pos limit 'c-<>-c-types-set)))
 
     ;; Update `c-state-cache' to the beginning of the region.  This will
     ;; make `c-beginning-of-syntax' go faster when it's used later on,



On Sun, Aug 28, 2022 at 14:33:08 +0900, Naofumi Yasufuku wrote:
> Naofumi Yasufuku <naofumi@yasufuku.dev> writes:

> > Hello,
> >
> > In the case of C++ partial template specialization [1], functions are
> > shown as variables.  Please look at the attached screenshots.
> >
> >   1. emacs -Q
> >   2. open attached C++ code "specialization.cc"
> >
> >   attachments:
> >   - NG_cc-partial-specialization.png
> >   - OK_cc-partial-specialization.png
> >   - specialization.cc
> >
> [..snip..]
> >
> > After a brief investigation, the attached cc-engine.el patch seems to
> > solve this issue at least, but it is not tested enough.
> >
> >   attachments:
> >   - 0001-cc-mode-Fix-function-fontification-in-the-case-of-C-.patch
> >

> Previous patch still has a problem with sizeof() specializations.
> Updated patch and screenshots are attached.

>   attachments:
>   - 0001-cc-mode-Fix-function-fontification-in-the-case-of-C-v2.patch
>   - NG_cc-partial-specialization-v1.png
>   - OK_cc-partial-specialization-v2.png
>   - specialization.cc

> -------------------------------------------------------------
> template<typename T1, size_t>
> class TwoSz {
> public:
>     TwoSz() {}
> private:
>     T1 _t1;
> };

> template<typename T>
> class TwoSz<T, sizeof(int)> {
> public:
>     TwoSz() {}
> private:
>     T _t1;
> };
> -------------------------------------------------------------
> $ ./specialization
> One<T>: primary
> One<char>: specialization
> Two<T1, T2>: primary
> Two<T, char>: specialization
> Two<T, T*>: specialization
> Two<T, T&>: specialization
> Two<T, T[]>: specialization
> Two<char, char*>: specialization
> Two<char, char&>: specialization
> Two<char, char[]>: specialization
> TwoSz<T1, size_t>: primary
> TwoSz<T, sizeof(int)>: specialization
> $
> -------------------------------------------------------------

> Best regards,
>   Naofumi

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#57318: 29.0.50; c++-mode: Functions are shown as variables: partial template specialization

[Naofumi Yasufuku]

[-- Attachment #1: Type: text/plain, Size: 2850 bytes --]

Hello Alan,

Alan Mackenzie <acm@muc.de> writes:

> Hello, Naofumi.
>
> Thank you indeed for your bug report, and thanks even more for
> diagnosing the cause and writing a patch!
>
> I'm truly astounded that you managed to debug this problem, hidden as it
> was in the fontification parts of CC Mode, which are difficult to run
> with the debugger.  Respect!
>

Thank you, I'm glad to hear that.

> Looking at your patch, I can see one or two problems with it.  The main
> one is that after encountering a template opener "<", I'm a bit worried
> about the accuracy of checking for the matching ">".
>
> Looking further into the problem, it seems the misfontification bug was
> triggered by the commas in the template expressions.  When there's a
> comma there, the (c-forward-<>-arglist ...) call (which "; Should always
> work") fails.  This failure is caused by the dynamic binding of
> c-restricted-<>-arglists to t.
>
> When this dynamic binding is instead at nil (rather than t), the
> fontification works properly, with functions fontified as functions.
> The reason for this faulty binding was fixing a bug report where
> scrolling a buffer containing lots of templates was very slow.  Binding
> c-restricted-<>-arglists to t "solved" that slowness.
>

Indeed.  I confirmed that avoiding (c-restricted-<>-arglists t) binding
solves this misfontification problem at least, but it makes scrolling
terribly slow...

> That slowness had been caused by inefficient scanning of the template
> structures.  I've now identified and implemented an alternative
> optimisation, which doesn't cause problems with commas in templates.
>
[..snip..]
> Can I ask you, please, to apply and test my proposed patch, which I
> enclose below.  Would you please test it on your real C++ source code,
> and either confirm it really works, or say what's still faulty about it.
> If there are any problems with applying the patch, feel free to send me
> personal email.
>

I've applied your patch.  It works well and solves misfontification
problem.  At the same time, I've not seen any noticeable performance
degradation by this patch so far.  Great.

  attachment: fix_c-restricted--arglists_verification.png

I came across this problem when I tried to compare the current
tree-sitter's fontification quality and performance with familiar
cc-mode by using very-fast flat_hash_map code [1][2].  Now problematic
fontification has gone.

> So I must apologize that I won't be using your patch, but I thoroughly
> appreciate the time you must have spent debugging the problem.
>

That's just fine with me.  I don't mind at all because I'm not an
expert.  Fixing the root cause should be done.

Best regards,
  Naofumi

[1] https://github.com/skarupke/flat_hash_map/blob/master/flat_hash_map.hpp
[2] https://probablydance.com/2017/02/26/i-wrote-the-fastest-hashtable/



[-- Attachment #2: verification --]
[-- Type: image/png, Size: 468337 bytes --]

bug#57318: 29.0.50; c++-mode: Functions are shown as variables: partial template specialization

[Alan Mackenzie]

Hello, Naofumi.

On Thu, Sep 01, 2022 at 01:01:56 +0900, Naofumi Yasufuku wrote:
> Hello Alan,

[ .... ]

> > When this dynamic binding is instead at nil (rather than t), the
> > fontification works properly, with functions fontified as functions.
> > The reason for this faulty binding was fixing a bug report where
> > scrolling a buffer containing lots of templates was very slow.  Binding
> > c-restricted-<>-arglists to t "solved" that slowness.


> Indeed.  I confirmed that avoiding (c-restricted-<>-arglists t) binding
> solves this misfontification problem at least, but it makes scrolling
> terribly slow...

Yes.  For the bug in 2019 for which I "fixed" this, the scrolling was
around a factor of 6 slower.

[ .... ]

> [..snip..]
> > Can I ask you, please, to apply and test my proposed patch, which I
> > enclose below.  Would you please test it on your real C++ source code,
> > and either confirm it really works, or say what's still faulty about it.
> > If there are any problems with applying the patch, feel free to send me
> > personal email.


> I've applied your patch.  It works well and solves misfontification
> problem.  At the same time, I've not seen any noticeable performance
> degradation by this patch so far.  Great.

Many thanks!

I've committed the patch to the standalone CC Mode repository and the
Emacs master branch at savannah.  I'm closing the bug with this post.

>   attachment: fix_c-restricted--arglists_verification.png

> I came across this problem when I tried to compare the current
> tree-sitter's fontification quality and performance with familiar
> cc-mode by using very-fast flat_hash_map code [1][2].  Now problematic
> fontification has gone.

In the long run, tree-sitter (or something like it) is going to be
superseding CC Mode.  Keeping up with the constantly evolving standards
in CC Mode has proven to be just too much work.  :-(

[ .... ]

> Best regards,
>   Naofumi

> [1] https://github.com/skarupke/flat_hash_map/blob/master/flat_hash_map.hpp
> [2] https://probablydance.com/2017/02/26/i-wrote-the-fastest-hashtable/

-- 
Alan Mackenzie (Nuremberg, Germany).