bug#36650: 27.0.50; CC Mode: Support C++ attributes

[Alan Mackenzie]

Hello, Óscar.

On Mon, Jul 15, 2019 at 17:17:27 +0200, Óscar Fuentes wrote:
> Alan Mackenzie <acm@muc.de> writes:

> > Yes.  I'll have a look at this.

> Thanks.

> >> In general, considering them part of the following token for indentation
> >> purposes and fontifying with some existing or new face should be enough.

> > I will probably end up treating attributes as syntactic whitespace.
> > They have no syntactic connection with the code they are embedded in,
> > any more than macros do.

The patch below (which should apply cleanly to the master branch) is a
first attempt at handling C++ attributes.

> I don't know how syntactic whitespace works on CC Mode, so just in case
> I'll mention that this code

> int foo([[maybe_unused]] int a,
>         int b);
        
> should not be formatted as

> int foo([[maybe_unused]] int a,
>                          int b);

Understood.  Happily, the code appears to do the right thing anyway,
without needing tedious fixing.  :-)

Could you please try out this patch, and let me know how well it works.

Thanks!



diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index cb88fc3e58..7963ab0d43 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -1827,45 +1827,122 @@ c-remove-is-and-in-sws
 (def-edebug-spec c-remove-is-and-in-sws t)
 
 ;; The type of literal position `end' is in a `before-change-functions'
-;; function - one of `c', `c++', `pound', or nil (but NOT `string').
+;; function - one of `c', `c++', `pound', `attribute', or nil (but NOT
+;; `string').
 (defvar c-sws-lit-type nil)
-;; A cons (START . STOP) of the bounds of the comment or CPP construct
+;; A cons (START . STOP) of the bounds of the comment or CPP construct, etc.,
 ;; enclosing END, if any, else nil.
 (defvar c-sws-lit-limits nil)
 
+(defmacro c-looking-at-c++-attribute ()
+  ;; If we're in C++ Mode, and point is at the [[ introducing an attribute,
+  ;; return the position of the end of the attribute, otherwise return nil.
+  ;; The match data are NOT preserved over this macro.
+  `(and
+    (c-major-mode-is 'c++-mode)
+    (looking-at "\\[\\[")
+    (save-excursion
+      (and
+       (c-go-list-forward)
+       (eq (char-before) ?\])
+       (eq (char-before (1- (point))) ?\])
+       (point)))))
+
+;; (defmacro c-enclosing-c++-attribute ()
+(defun c-enclosing-c++-attribute ()
+  ;; If we're in C++ Mode, and point is within a correctly balanced [[ ... ]]
+  ;; attribute structure, return a cons of its starting and ending positions.
+  ;; Otherwise, return nil.  We use the c-{in,is}-sws-face text properties for
+  ;; this determination, this macro being intended only for use in the *-sws-*
+  ;; functions and macros.  The match data are NOT preserved over this macro.
+  (let (attr-end pos-is-sws)
+     (and
+      (c-major-mode-is 'c++-mode)
+      (> (point) (point-min))
+      (setq pos-is-sws
+           (if (get-text-property (1- (point)) 'c-is-sws)
+               (1- (point))
+             (1- (previous-single-property-change
+                  (point) 'c-is-sws nil (point-min)))))
+      (save-excursion
+       (goto-char pos-is-sws)
+       (setq attr-end (c-looking-at-c++-attribute)))
+      (> attr-end (point))
+      (cons pos-is-sws attr-end))))
+
+(defun c-slow-enclosing-c++-attribute ()
+  ;; Like `c-enclosing-c++-attribute', but does not depend on the c-i[ns]-sws
+  ;; properties being set.
+  (and
+   (c-major-mode-is 'c++-mode)
+   (save-excursion
+     (let ((paren-state (c-parse-state))
+          cand)
+       (while
+          (progn
+            (setq cand
+                  (catch 'found-cand
+                    (while (cdr paren-state)
+                      (when (and (numberp (car paren-state))
+                                 (numberp (cadr paren-state))
+                                 (eq (car paren-state)
+                                     (1+ (cadr paren-state)))
+                                 (eq (char-after (car paren-state)) ?\[)
+                                 (eq (char-after (cadr paren-state)) ?\[))
+                        (throw 'found-cand (cadr paren-state)))
+                      (setq paren-state (cdr paren-state)))))
+            (and cand
+                 (not
+                  (and (c-go-list-forward cand)
+                       (eq (char-before) ?\])
+                       (eq (char-before (1- (point))) ?\])))))
+        (setq paren-state (cdr paren-state)))
+       (and cand (cons cand (point)))))))
+
 (defun c-invalidate-sws-region-before (beg end)
   ;; Called from c-before-change.  BEG and END are the bounds of the change
   ;; region, the standard parameters given to all before-change-functions.
   ;;
-  ;; Note whether END is inside a comment, CPP construct, or noise macro, and
-  ;; if so note its bounds in `c-sws-lit-limits' and type in `c-sws-lit-type'.
+  ;; Note whether END is inside a comment, CPP construct, C++ attribute, or
+  ;; noise macro, and if so note its bounds in `c-sws-lit-limits' and type in
+  ;; `c-sws-lit-type'.
   (setq c-sws-lit-type nil
        c-sws-lit-limits nil)
-  (save-excursion
-    (goto-char end)
-    (let* ((limits (c-literal-limits))
-          (lit-type (c-literal-type limits)))
-      (cond
-       ((memq lit-type '(c c++))
-       (setq c-sws-lit-type lit-type
-             c-sws-lit-limits limits))
-       ((c-beginning-of-macro)
-       (setq c-sws-lit-type 'pound
-             c-sws-lit-limits (cons (point)
-                                    (progn (c-end-of-macro) (point)))))
-       ((progn (skip-syntax-backward "w_")
-              (looking-at c-noise-macro-name-re))
-       (setq c-sws-lit-type 'noise
-             c-sws-lit-limits (cons (match-beginning 1) (match-end 1))))
-       (t))))
-  (save-excursion
-    (goto-char beg)
-    (skip-syntax-backward "w_")
-    (when (looking-at c-noise-macro-name-re)
-      (setq c-sws-lit-type 'noise)
-      (if (consp c-sws-lit-limits)
-         (setcar c-sws-lit-limits (match-beginning 1))
-       (setq c-sws-lit-limits (cons (match-beginning 1) (match-end 1)))))))
+  (save-match-data
+    (save-excursion
+      (goto-char end)
+      (let* ((limits (c-literal-limits))
+            (lit-type (c-literal-type limits)))
+       (cond
+        ((memq lit-type '(c c++))
+         (setq c-sws-lit-type lit-type
+               c-sws-lit-limits limits))
+        ((c-beginning-of-macro)
+         (setq c-sws-lit-type 'pound
+               c-sws-lit-limits (cons (point)
+                                      (progn (c-end-of-macro) (point)))))
+        ((eq lit-type 'string))
+        ((setq c-sws-lit-limits (c-enclosing-c++-attribute))
+         (setq c-sws-lit-type 'attribute))
+        ((progn (skip-syntax-backward "w_")
+                (looking-at c-noise-macro-name-re))
+         (setq c-sws-lit-type 'noise
+               c-sws-lit-limits (cons (match-beginning 1) (match-end 1))))
+        (t))))
+    (save-excursion
+      (goto-char beg)
+      (let ((attr-limits (c-enclosing-c++-attribute)))
+       (if attr-limits
+           (if (consp c-sws-lit-limits)
+               (setcar c-sws-lit-limits (car attr-limits))
+             (setq c-sws-lit-limits attr-limits))
+         (skip-syntax-backward "w_")
+         (when (looking-at c-noise-macro-name-re)
+           (setq c-sws-lit-type 'noise)
+           (if (consp c-sws-lit-limits)
+               (setcar c-sws-lit-limits (match-beginning 1))
+             (setq c-sws-lit-limits (cons (match-beginning 1)
+                                          (match-end 1))))))))))
 
 (defun c-invalidate-sws-region-after-del (beg end _old-len)
   ;; Text has been deleted, OLD-LEN characters of it starting from position
@@ -1940,7 +2017,7 @@ c-invalidate-sws-region-after
       (when (and (eolp) (not (eobp)))
        (setq end (1+ (point)))))
 
-    (when (eq c-sws-lit-type 'noise)
+    (when (memq c-sws-lit-type '(noise attribute))
       (setq beg (car c-sws-lit-limits)
            end (cdr c-sws-lit-limits))) ; This last setting may be redundant.
 
@@ -1990,6 +2067,8 @@ c-forward-sws
     (when (or (looking-at c-syntactic-ws-start)
              (and c-opt-cpp-prefix
                   (looking-at c-noise-macro-name-re))
+             (and (c-major-mode-is 'c++-mode)
+                  (looking-at "\\[\\["))
              (looking-at c-doc-line-join-re))
 
       (setq rung-end-pos (min (1+ (point)) (point-max)))
@@ -2126,6 +2205,16 @@ c-forward-sws
              (goto-char (match-end 1))
              (not (eobp)))
 
+            ((and (c-major-mode-is 'c++-mode)
+                  (looking-at "\\[\\[")
+                  (save-excursion
+                    (and (c-go-list-forward)
+                         (eq (char-before) ?\])
+                         (eq (char-before (1- (point))) ?\])
+                         (setq next-rung-pos (point))))
+                  (goto-char next-rung-pos))
+             (not (eobp)))
+
             ((looking-at c-doc-line-join-re)
              ;; Skip over a line join in (e.g.) Pike autodoc.
              (goto-char (match-end 0))
@@ -2240,6 +2329,13 @@ c-backward-sws
                      (memq (char-before) c-doc-line-join-end-ch) ; For speed.
                      (re-search-backward doc-line-join-here
                                          (c-point 'bopl) t))
+                    (and
+                     (c-major-mode-is 'c++-mode)
+                     (eq (char-before) ?\])
+                     (eq (char-before (1- (point))) ?\])
+                     (save-excursion
+                       (and (c-go-list-backward)
+                            (looking-at "\\(\\)\\[\\["))))
                     (progn
                       (backward-char)
                       (or (looking-at c-syntactic-ws-end)
@@ -2250,7 +2346,7 @@ c-backward-sws
       ;; Try to find a rung position in the simple ws preceding point, so that
       ;; we can get a cache hit even if the last bit of the simple ws has
       ;; changed recently.
-      (setq simple-ws-beg (or (match-end 1) ; Noise macro
+      (setq simple-ws-beg (or (match-end 1) ; Noise macro, etc.
                              (match-end 0))) ; c-syntactic-ws-end
       (skip-chars-backward " \t\n\r\f\v")
       (if (setq rung-is-marked (text-property-any
@@ -2388,6 +2484,16 @@ c-backward-sws
              (goto-char next-rung-pos)
              t)
 
+            ((and (c-major-mode-is 'c++-mode)
+                  (eq (char-before) ?\])
+                  (eq (char-before (1- (point))) ?\])
+                  (save-excursion
+                    (and (c-go-list-backward)
+                         (setq next-rung-pos (point))
+                         (looking-at "\\[\\["))))
+             (goto-char next-rung-pos)
+             t)
+
             ((and
               (memq (char-before) c-doc-line-join-end-ch) ; For speed.
               (re-search-backward doc-line-join-here (c-point 'bopl) t)))))
diff --git a/lisp/progmodes/cc-mode.el b/lisp/progmodes/cc-mode.el
index 5ae7e0f09d..a5e158933b 100644
--- a/lisp/progmodes/cc-mode.el
+++ b/lisp/progmodes/cc-mode.el
@@ -2158,9 +2158,11 @@ c-fl-decl-end
   ;; count as being in a declarator (on pragmatic grounds).
   (goto-char pos)
   (let ((lit-start (c-literal-start))
-       pos1)
+       enclosing-attribute pos1)
     (unless lit-start
       (c-backward-syntactic-ws)
+      (when (setq enclosing-attribute (c-slow-enclosing-c++-attribute))
+       (goto-char (car enclosing-attribute))) ; Only happens in C++ Mode.
       (when (setq pos1 (c-on-identifier))
        (goto-char pos1)
        (let ((lim (save-excursion


-- 
Alan Mackenzie (Nuremberg, Germany).