From 3096437593ca6d1ea07809f7d0e2198705f20e55 Mon Sep 17 00:00:00 2001
From: Alan Mackenzie <acm@muc.de>
Date: Thu, 24 Dec 2020 11:29:27 +0000
Subject: [PATCH] CC Mode: introduce a new cache for brace structures.  This
 fixes bug #45248

Also fix three infinite loops.  The new cache accelerates backward searches
for struct beginnings in c-looking-at-or-maybe-in-bracelist.

* lisp/progmodes/cc-engine.el (c-beginning-of-statement-1): In the final loop
over unary operators, add a check (> (point) lim) to avoid certain infinite
loops.
(c-beginning-of-decl-1): In the first loop add a similar check on point and
lim.
(c-laomib-loop): New function extracted from
c-looking-at-or-maybe-in-bracelist.
(c-laomib-cache): New buffer local variable.
(c-laomib-get-cache, c-laomib-put-cache, c-laomib-fix-elt)
(c-laomib-invalidate-cache): New functions which implement the cache.
(c-looking-at-or-maybe-in-bracelist): Replace two invocations of
c-go-up-list-backwards with calls to c-parse-state.  Extract the new function
c-laomib-loop.  Insert code which calls c-laomib-loop minimally, with the help
of the new cache.

* lisp/progmodes/cc-mode.el (c-basic-common-init): Initialise the new cach
(at mode start).
(c-before-change): Invalidate the new cache.
(c-fl-decl-start): Add an extra check (> (point) bod-lim) to prevent looping.
Determine the enclosing brace to pass as arguments to
c-looking-at-or-maybe-in-bracelist.
---
 lisp/progmodes/cc-engine.el | 332 ++++++++++++++++++++++++++----------
 lisp/progmodes/cc-mode.el   |  34 +++-
 2 files changed, 266 insertions(+), 100 deletions(-)

diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index 218bbb47cd5..51f620ea1f0 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -1414,12 +1414,14 @@ comment at the start of cc-engine.el for more info."
 	    (setq ret 'label)))
 
       ;; Skip over the unary operators that can start the statement.
-      (while (progn
-	       (c-backward-syntactic-ws lim)
-	       ;; protect AWK post-inc/decrement operators, etc.
-	       (and (not (c-at-vsemi-p (point)))
-		    (/= (skip-chars-backward "-.+!*&~@`#") 0)))
+      (while (and (> (point) lim)
+		  (progn
+		    (c-backward-syntactic-ws lim)
+		    ;; protect AWK post-inc/decrement operators, etc.
+		    (and (not (c-at-vsemi-p (point)))
+			 (/= (skip-chars-backward "-.+!*&~@`#") 0))))
 	(setq pos (point)))
+
       (goto-char pos)
       ret)))
 
@@ -3567,8 +3569,9 @@ mhtml-mode."
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Defuns which analyze the buffer, yet don't change `c-state-cache'.
 (defun c-get-fallback-scan-pos (here)
-  ;; Return a start position for building `c-state-cache' from
-  ;; scratch.  This will be at the top level, 2 defuns back.
+  ;; Return a start position for building `c-state-cache' from scratch.  This
+  ;; will be at the top level, 2 defuns back.  Return nil if we don't find
+  ;; these defun starts a reasonable way back.
   (save-excursion
     (save-restriction
       (when (> here (* 10 c-state-cache-too-far))
@@ -11177,6 +11180,7 @@ comment at the start of cc-engine.el for more info."
 		  (c-backward-syntactic-ws lim)
 		  (not (or (memq (char-before) '(?\; ?} ?: nil))
 			   (c-at-vsemi-p))))
+		(not (and lim (<= (point) lim)))
 		(save-excursion
 		  (backward-char)
 		  (not (looking-at "\\s(")))
@@ -11615,6 +11619,195 @@ comment at the start of cc-engine.el for more info."
     (or (looking-at c-brace-list-key)
 	(progn (goto-char here) nil))))
 
+(defun c-laomib-loop (lim)
+  ;; The "expensive" loop from `c-looking-at-or-maybe-in-bracelist'.  Move
+  ;; backwards over comma separated sexps as far as possible, but no further
+  ;; than LIM, which may be nil, meaning no limit.  Return the final value of
+  ;; `braceassignp', which is t if we encountered "= {", usually nil
+  ;; otherwise.
+  (let ((braceassignp 'dontknow)
+	  (class-key
+	   ;; Pike can have class definitions anywhere, so we must
+	   ;; check for the class key here.
+	   (and (c-major-mode-is 'pike-mode)
+		c-decl-block-key)))
+    (while (eq braceassignp 'dontknow)
+      (cond ((eq (char-after) ?\;)
+	     (setq braceassignp nil))
+	    ((and class-key
+		  (looking-at class-key))
+	     (setq braceassignp nil))
+	    ((and c-has-compound-literals
+		  (looking-at c-return-key))
+	     (setq braceassignp t)
+	     nil)
+	    ((eq (char-after) ?=)
+	     ;; We've seen a =, but must check earlier tokens so
+	     ;; that it isn't something that should be ignored.
+	     (setq braceassignp 'maybe)
+	     (while (and (eq braceassignp 'maybe)
+			 (zerop (c-backward-token-2 1 t lim)))
+	       (setq braceassignp
+		     (cond
+		      ;; Check for operator =
+		      ((and c-opt-op-identifier-prefix
+			    (looking-at c-opt-op-identifier-prefix))
+		       nil)
+		      ;; Check for `<opchar>= in Pike.
+		      ((and (c-major-mode-is 'pike-mode)
+			    (or (eq (char-after) ?`)
+				;; Special case for Pikes
+				;; `[]=, since '[' is not in
+				;; the punctuation class.
+				(and (eq (char-after) ?\[)
+				     (eq (char-before) ?`))))
+		       nil)
+		      ((looking-at "\\s.") 'maybe)
+		      ;; make sure we're not in a C++ template
+		      ;; argument assignment
+		      ((and
+			(c-major-mode-is 'c++-mode)
+			(save-excursion
+			  (let ((here (point))
+				(pos< (progn
+					(skip-chars-backward "^<>")
+					(point))))
+			    (and (eq (char-before) ?<)
+				 (not (c-crosses-statement-barrier-p
+				       pos< here))
+				 (not (c-in-literal))
+				 ))))
+		       nil)
+		      (t t)))))
+	    ((and
+	      (c-major-mode-is 'c++-mode)
+	      (eq (char-after) ?\[)
+	      ;; Be careful of "operator []"
+	      (not (save-excursion
+		     (c-backward-token-2 1 nil lim)
+		     (looking-at c-opt-op-identifier-prefix))))
+	     (setq braceassignp t)
+	     nil))
+      (when (eq braceassignp 'dontknow)
+	(cond ((and
+		(not (eq (char-after) ?,))
+		(save-excursion
+		  (c-backward-syntactic-ws)
+		  (eq (char-before) ?})))
+	       (setq braceassignp nil))
+	      ((/= (c-backward-token-2 1 t lim) 0)
+	       (if (save-excursion
+		     (and c-has-compound-literals
+			  (eq (c-backward-token-2 1 nil lim) 0)
+			  (eq (char-after) ?\()))
+		   (setq braceassignp t)
+		 (setq braceassignp nil))))))
+    braceassignp))
+
+;; The following variable is a cache of up to four entries, each entry of
+;; which is a list representing a call to c-laomib-loop.  It contains the
+;; following elements:
+;; 0: `lim' argument - used as an alist key, never nil.
+;; 1: Position in buffer where the scan started.
+;; 2: Position in buffer where the scan ended.
+;; 3: Result of the call to `c-laomib-loop'.
+(defvar c-laomib-cache nil)
+(make-variable-buffer-local 'c-laomib-cache)
+
+(defun c-laomib-get-cache (containing-sexp)
+  ;; Get an element from `c-laomib-cache' matching CONTAINING-SEXP.
+  ;; Return that element or nil if one wasn't found.
+  (let ((elt (assq containing-sexp c-laomib-cache)))
+    (when elt
+      ;; Move the fetched `elt' to the front of the cache.
+      (setq c-laomib-cache (delq elt c-laomib-cache))
+      (push elt c-laomib-cache)
+      elt)))
+
+(defun c-laomib-put-cache (lim start end result)
+  ;; Insert a new element into `c-laomib-cache', removing another element to
+  ;; make room, if necessary.  The four parameters LIM, START, END, RESULT are
+  ;; the components of the new element (see comment for `c-laomib-cache').
+  ;; The return value is of no significance.
+  (when lim
+    (let ((old-elt (assq lim c-laomib-cache))
+	  ;; (elt (cons containing-sexp (cons start nil)))
+	  (new-elt (list lim start end result))
+	  big-ptr
+	  (cur-ptr c-laomib-cache)
+	  togo togo-ptr (size 0) cur-size
+	  )
+      (if old-elt (setq c-laomib-cache (delq old-elt c-laomib-cache)))
+
+      (while (>= (length c-laomib-cache) 4)
+	;; We delete the least recently used elt which doesn't enclose START,
+	;; or..
+	(dolist (elt c-laomib-cache)
+	  (if (or (<= start (cadr elt))
+		  (> start (car (cddr elt))))
+	      (setq togo elt)))
+
+	;; ... delete the least recently used elt which isn't the biggest.
+	(when (not togo)
+	  (while (cdr cur-ptr)
+	    (setq cur-size (- (nth 2 (cadr cur-ptr)) (car (cadr cur-ptr))))
+	    (when (> cur-size size)
+	      (setq size cur-size
+		    big-ptr cur-ptr))
+	    (setq cur-ptr (cdr cur-ptr)))
+	  (setq togo (if (cddr big-ptr)
+			 (car (last big-ptr))
+		       (car big-ptr))))
+
+	(setq c-laomib-cache (delq togo c-laomib-cache)))
+
+      (push new-elt c-laomib-cache))))
+
+(defun c-laomib-fix-elt (lwm elt paren-state)
+  ;; Correct a c-laomib-cache entry ELT with respect to buffer changes, either
+  ;; doing nothing, signalling it is to be deleted, or replacing its start
+  ;; point with one lower in the buffer than LWM.  PAREN-STATE is the paren
+  ;; state at LWM.  Return the corrected entry, or nil (if it needs deleting).
+  ;; Note that corrections are made by `setcar'ing the original structure,
+  ;; which thus remains intact.
+  (cond
+   ((or (not lwm) (> lwm (cadr elt)))
+    elt)
+   ((<= lwm (nth 2 elt))
+    nil)
+   (t
+    (let (cur-brace)
+      ;; Search for the last brace in `paren-state' before (car `lim').  This
+      ;; brace will become our new 2nd element of `elt'.
+      (while
+	  ;; Search one brace level per iteration.
+	  (and paren-state
+	       (progn
+		 ;; (setq cur-brace (c-laomib-next-BRACE paren-state))
+		 (while
+		     ;; Go past non-brace levels, one per iteration.
+		     (and paren-state
+			  (not (eq (char-after
+				    (c-state-cache-top-lparen paren-state))
+				   ?{)))
+		   (setq paren-state (cdr paren-state)))
+		 (cadr paren-state))
+	       (> (c-state-cache-top-lparen (cdr paren-state)) (car elt)))
+	(setq paren-state (cdr paren-state)))
+      (when (cadr paren-state)
+	(setcar (cdr elt) (c-state-cache-top-lparen paren-state))
+	elt)))))
+
+(defun c-laomib-invalidate-cache (beg _end)
+  ;; Called from late in c-before-change.  Amend `c-laomib-cache' to remove
+  ;; details pertaining to the buffer after position BEG.
+  (save-excursion
+    (goto-char beg)
+    (let ((paren-state (c-parse-state)))
+      (dolist (elt c-laomib-cache)
+	(when (not (c-laomib-fix-elt beg elt paren-state))
+	  (setq c-laomib-cache (delq elt c-laomib-cache)))))))
+
 (defun c-looking-at-or-maybe-in-bracelist (&optional containing-sexp lim)
   ;; Point is at an open brace.  If this starts a brace list, return a list
   ;; whose car is the buffer position of the start of the construct which
@@ -11635,14 +11828,10 @@ comment at the start of cc-engine.el for more info."
   ;; Here, "brace list" does not include the body of an enum.
   (save-excursion
     (let ((start (point))
-	  (class-key
-	   ;; Pike can have class definitions anywhere, so we must
-	   ;; check for the class key here.
-	   (and (c-major-mode-is 'pike-mode)
-		c-decl-block-key))
 	  (braceassignp 'dontknow)
 	  inexpr-brace-list bufpos macro-start res pos after-type-id-pos
-	  in-paren parens-before-brace)
+	  in-paren parens-before-brace
+	  paren-state paren-pos)
 
       (setq res (c-backward-token-2 1 t lim))
       ;; Checks to do only on the first sexp before the brace.
@@ -11651,8 +11840,10 @@ comment at the start of cc-engine.el for more info."
 	       (cond
 		((and (or (not (eq res 0))
 			  (eq (char-after) ?,))
-		      (c-go-up-list-backward nil lim) ; FIXME!!! Check ; `lim' 2016-07-12.
-		      (eq (char-after) ?\())
+		      (setq paren-state (c-parse-state))
+		      (setq paren-pos (c-pull-open-brace paren-state))
+		      (eq (char-after paren-pos) ?\())
+		 (goto-char paren-pos)
 		 (setq braceassignp 'c++-noassign
 		       in-paren 'in-paren))
 		((looking-at c-pre-id-bracelist-key)
@@ -11669,9 +11860,11 @@ comment at the start of cc-engine.el for more info."
 		 (cond
 		  ((or (not (eq res 0))
 		       (eq (char-after) ?,))
-		   (and (c-go-up-list-backward nil lim) ; FIXME!!! Check `lim' 2016-07-12.
-			(eq (char-after) ?\()
-			(setq in-paren 'in-paren)))
+		   (and (setq paren-state (c-parse-state))
+			(setq paren-pos (c-pull-open-brace paren-state))
+			(eq (char-after paren-pos) ?\()
+			(setq in-paren 'in-paren)
+			(goto-char paren-pos)))
 		  ((looking-at c-pre-id-bracelist-key))
 		  ((looking-at c-return-key))
 		  (t (setq after-type-id-pos (point))
@@ -11724,79 +11917,36 @@ comment at the start of cc-engine.el for more info."
 
        (t
 	(goto-char pos)
-	;; Checks to do on all sexps before the brace, up to the
-	;; beginning of the statement.
-	(while (eq braceassignp 'dontknow)
-	  (cond ((eq (char-after) ?\;)
-		 (setq braceassignp nil))
-		((and class-key
-		      (looking-at class-key))
-		 (setq braceassignp nil))
-		((and c-has-compound-literals
-		      (looking-at c-return-key))
-		 (setq braceassignp t)
-		 nil)
-		((eq (char-after) ?=)
-		 ;; We've seen a =, but must check earlier tokens so
-		 ;; that it isn't something that should be ignored.
-		 (setq braceassignp 'maybe)
-		 (while (and (eq braceassignp 'maybe)
-			     (zerop (c-backward-token-2 1 t lim)))
-		   (setq braceassignp
-			 (cond
-			  ;; Check for operator =
-			  ((and c-opt-op-identifier-prefix
-				(looking-at c-opt-op-identifier-prefix))
-			   nil)
-			  ;; Check for `<opchar>= in Pike.
-			  ((and (c-major-mode-is 'pike-mode)
-				(or (eq (char-after) ?`)
-				    ;; Special case for Pikes
-				    ;; `[]=, since '[' is not in
-				    ;; the punctuation class.
-				    (and (eq (char-after) ?\[)
-					 (eq (char-before) ?`))))
-			   nil)
-			  ((looking-at "\\s.") 'maybe)
-			  ;; make sure we're not in a C++ template
-			  ;; argument assignment
-			  ((and
-			    (c-major-mode-is 'c++-mode)
-			    (save-excursion
-			      (let ((here (point))
-				    (pos< (progn
-					    (skip-chars-backward "^<>")
-					    (point))))
-				(and (eq (char-before) ?<)
-				     (not (c-crosses-statement-barrier-p
-					   pos< here))
-				     (not (c-in-literal))
-				     ))))
-			   nil)
-			  (t t)))))
-		((and
-		  (c-major-mode-is 'c++-mode)
-		  (eq (char-after) ?\[)
-		 ;; Be careful of "operator []"
-		  (not (save-excursion
-			 (c-backward-token-2 1 nil lim)
-			 (looking-at c-opt-op-identifier-prefix))))
-		 (setq braceassignp t)
-		 nil))
-	  (when (eq braceassignp 'dontknow)
-	    (cond ((and
-		    (not (eq (char-after) ?,))
-		    (save-excursion
-		      (c-backward-syntactic-ws)
-		      (eq (char-before) ?})))
-		   (setq braceassignp nil))
-		  ((/= (c-backward-token-2 1 t lim) 0)
-		   (if (save-excursion
-			 (and c-has-compound-literals
-			      (eq (c-backward-token-2 1 nil lim) 0)
-			      (eq (char-after) ?\()))
-		       (setq braceassignp t)
-		     (setq braceassignp nil))))))
+	(when (eq braceassignp 'dontknow)
+	  (let* ((cache-entry (and containing-sexp
+				   (c-laomib-get-cache containing-sexp)))
+		 (lim2 (or (cadr cache-entry) lim))
+		 sub-bassign-p)
+	    (if cache-entry
+		(cond
+		 ((<= (point) (cadr cache-entry))
+		  ;; We're inside the region we've already scanned over, so
+		  ;; just go to that scan's end position.
+		  (goto-char (nth 2 cache-entry))
+		  (setq braceassignp (nth 3 cache-entry)))
+		 ((> (point) (cadr cache-entry))
+		  ;; We're beyond the previous scan region, so just scan as
+		  ;; far as the end of that region.
+		  (setq sub-bassign-p (c-laomib-loop lim2))
+		  (if (<= (point) (cadr cache-entry))
+		      (progn
+			(c-laomib-put-cache containing-sexp
+					    start (nth 2 cache-entry)
+					    (nth 3 cache-entry) ;; sub-bassign-p
+					    )
+			(setq braceassignp (nth 3 cache-entry))
+			(goto-char (nth 2 cache-entry)))
+		    (setq braceassignp sub-bassign-p)))
+		 (t))
+
+	      (setq braceassignp (c-laomib-loop lim))
+	      (when lim
+		(c-laomib-put-cache lim start (point) braceassignp)))))
 
 	(cond
 	 (braceassignp
diff --git a/lisp/progmodes/cc-mode.el b/lisp/progmodes/cc-mode.el
index 7a111017074..f6d36f5670c 100644
--- a/lisp/progmodes/cc-mode.el
+++ b/lisp/progmodes/cc-mode.el
@@ -639,6 +639,8 @@ that requires a literal mode spec at compile time."
   ;; doesn't work with filladapt but it's better than nothing.
   (set (make-local-variable 'fill-paragraph-function) 'c-fill-paragraph)
 
+  ;; Initialize the cache for `c-looking-at-or-maybe-in-bracelist'.
+  (setq c-laomib-cache nil)
   ;; Initialize the three literal sub-caches.
   (c-truncate-lit-pos-cache 1)
   ;; Initialize the cache of brace pairs, and opening braces/brackets/parens.
@@ -2054,7 +2056,9 @@ Note that this is a strict tail, so won't match, e.g. \"0x....\".")
 		(if c-get-state-before-change-functions
 		    (mapc (lambda (fn)
 			    (funcall fn beg end))
-			  c-get-state-before-change-functions))))
+			  c-get-state-before-change-functions))
+
+		(c-laomib-invalidate-cache beg end)))
 	  (c-clear-string-fences))))
     (c-truncate-lit-pos-cache beg)
     ;; The following must be done here rather than in `c-after-change'
@@ -2205,7 +2209,8 @@ Note that this is a strict tail, so won't match, e.g. \"0x....\".")
 	old-pos
 	(new-pos pos)
 	capture-opener
-	bod-lim bo-decl)
+	bod-lim bo-decl
+	paren-state containing-brace)
     (goto-char (c-point 'bol new-pos))
     (unless lit-start
       (setq bod-lim (c-determine-limit 500))
@@ -2224,12 +2229,16 @@ Note that this is a strict tail, so won't match, e.g. \"0x....\".")
 	   (setq old-pos (point))
 	   (let (pseudo)
 	     (while
-		 (progn
-		   (c-syntactic-skip-backward "^;{}" bod-lim t)
-		   (and (eq (char-before) ?})
-			(save-excursion
-			  (backward-char)
-			  (setq pseudo (c-cheap-inside-bracelist-p (c-parse-state))))))
+		 (and
+		  ;; N.B. `c-syntactic-skip-backward' doesn't check (> (point)
+		  ;; lim) and can loop if that's not the case.
+		  (> (point) bod-lim)
+		  (progn
+		    (c-syntactic-skip-backward "^;{}" bod-lim t)
+		    (and (eq (char-before) ?})
+			 (save-excursion
+			   (backward-char)
+			   (setq pseudo (c-cheap-inside-bracelist-p (c-parse-state)))))))
 	       (goto-char pseudo))
 	     t)
 	   (> (point) bod-lim)
@@ -2262,7 +2271,14 @@ Note that this is a strict tail, so won't match, e.g. \"0x....\".")
 		      (and (eq (char-before) ?{)
 			   (save-excursion
 			     (backward-char)
-			     (consp (c-looking-at-or-maybe-in-bracelist))))
+			     (setq paren-state (c-parse-state))
+			     (while
+				 (and
+				  (setq containing-brace
+					(c-pull-open-brace paren-state))
+				  (not (eq (char-after containing-brace) ?{))))
+			     (consp (c-looking-at-or-maybe-in-bracelist
+				     containing-brace containing-brace))))
 		      )))
 	   (not (bobp)))
 	(backward-char))		; back over (, [, <.