CC Mode internal cache: Handle a cache pos being inside a two-char construct.

Cache c-state-semi-nonlit-pos-cache was failing when a cache position was,
e.g., between the two characters of an opening comment "/*", and additionally
there were an odd number of quote marks (apostrophes) in the comment.  This
happened in .../src/xdisp.c in the Emacs master branch around 2017-05-02 at
buffer position 615001.

* lisp/progmodes/cc-defs.el (c-emacs-features): Repurpose symbol
pps-extended-state to mean that there are at least 11 elements in the parser
state.

* lisp/progmodes/cc-engine.el (c-cache-to-parse-ps-state)
(c-parse-ps-state-to-cache): Rewrite these to use enhanced cache element list
types which indicate potentially being inside two-char constructs.
(c-parse-ps-state-below): Rewrite to use the new versions of the above two
functions.

2 files changed, 125 insertions, 57 deletions

diff --git a/lisp/progmodes/cc-defs.el b/lisp/progmodes/cc-defs.el
index 8dd56106af4..dd8f8afc6a3 100644
--- a/lisp/progmodes/cc-defs.el
+++ b/lisp/progmodes/cc-defs.el
@@ -1914,14 +1914,18 @@ non-nil, a caret is prepended to invert the set."
         (set-buffer-modified-p nil))
       (kill-buffer buf))
 
-    ;; See if `parse-partial-sexp' returns the eighth element.
-    (if (c-safe (>= (length (save-excursion
-                              (parse-partial-sexp (point) (point))))
-                    10))
-        (setq list (cons 'pps-extended-state list))
-      (error (concat
-              "CC Mode is incompatible with this version of Emacs - "
-              "`parse-partial-sexp' has to return at least 10 elements.")))
+    ;; Check how many elements `parse-partial-sexp' returns.
+    (let ((ppss-size (or (c-safe (length
+                                  (save-excursion
+                                    (parse-partial-sexp (point) (point)))))
+                         0)))
+      (cond
+       ((>= ppss-size 11) (setq list (cons 'pps-extended-state list)))
+       ((>= ppss-size 10))
+       (t (error
+           (concat
+            "CC Mode is incompatible with this version of Emacs - "
+            "`parse-partial-sexp' has to return at least 10 elements.")))))
 
     ;;(message "c-emacs-features: %S" list)
     list)
@@ -1944,10 +1948,9 @@ might be present:
                     (i.e. the syntax class `!').
 `gen-string-delim'  Generic string delimiters work
                     (i.e. the syntax class `|').
-`pps-extended-state' `parse-partial-sexp' returns a list with at least 10
-                    elements, i.e. it contains the position of the start of
-                    the last comment or string.  It's always set - CC Mode
-                    no longer works in emacsen without this feature.
+`pps-extended-state' `parse-partial-sexp' returns a list with at least 11
+                    elements, i.e. it indicates having stopped after the
+                    first character of a potential two-char construct.
 `posix-char-classes' The regexp engine understands POSIX character classes.
 `col-0-paren'       It's possible to turn off the ad-hoc rule that a paren
                     in column zero is the start of a defun.
diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index 4af7c359747..6d7bab7a65c 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -2575,17 +2575,24 @@ comment at the start of cc-engine.el for more info."
 
 (defun c-cache-to-parse-ps-state (elt)
   ;; Create a list suitable to use as the old-state parameter to
-  ;; `parse-partial-sexp', out of ELT.  ELT is either just a number, a buffer
-  ;; position, or it is a list (POS TYPE STARTING-POS).  Here POS is the
-  ;; buffer position the other elements are pertinent for, TYPE is either 'c
-  ;; or 'c++ (for a comment) or a character (for a string delimiter) or t
-  ;; (meaning a string fence opened the string), STARTING-POS is the starting
-  ;; position of the comment or string.
-  (if (consp elt)
+  ;; `parse-partial-sexp', out of ELT, a member of
+  ;; `c-state-semi-nonlit-pos-cache'.  ELT is either just a number, or a list
+  ;; with 2, 3, or 4 members (See `c-parse-ps-state-to-cache').  That number
+  ;; or the car of the list is the "position element" of ELT, the position
+  ;; where ELT is valid.
+  ;;
+  ;; POINT is left at the postition for which the returned state is valid.  It
+  ;; will be either the position element of ELT, or one character before
+  ;; that.  (The latter happens in Emacs <= 25 and XEmacs, when ELT indicates
+  ;; its position element directly follows a potential first character of a
+  ;; two char construct (such as a comment opener or an escaped character).)
+  (if (and (consp elt) (>= (length elt) 3))
+      ;; Inside a string or comment
       (let ((depth 0) (containing nil) (last nil)
             in-string in-comment (after-quote nil)
             (min-depth 0) com-style com-str-start (intermediate nil)
-            (between-syntax nil)
+            (char-1 (nth 3 elt))        ; first char of poss. 2-char construct
+            (pos (car elt))
             (type (cadr elt)))
         (setq com-str-start (car (cddr elt)))
         (cond
@@ -2596,28 +2603,88 @@ comment at the start of cc-engine.el for more info."
                 com-style (if (eq type 'c++) 1 nil)))
          (t (c-benign-error "Invalid type %s in c-cache-to-parse-ps-state"
                             elt)))
-        (list depth containing last
-              in-string in-comment after-quote
-              min-depth com-style com-str-start
-              intermediate nil))
-    (copy-tree '(0 nil nil nil nil nil 0 nil nil nil nil))))
+        (if (memq 'pps-extended-state c-emacs-features)
+            (progn
+              (goto-char pos)
+              (list depth containing last
+                    in-string in-comment after-quote
+                    min-depth com-style com-str-start
+                    intermediate char-1))
+          (goto-char (if char-1
+                         (1- pos)
+                       pos))
+          (list depth containing last
+                in-string in-comment nil
+                min-depth com-style com-str-start
+                intermediate)))
+
+    ;; Not in a string or comment.
+    (if (memq 'pps-extended-state c-emacs-features)
+        (progn
+          (goto-char (if (consp elt) (car elt) elt))
+          (list 0 nil nil nil nil
+                (and (consp elt) (eq (nth 1 elt) 9)) ; 9 is syntax code for "escape".
+                0 nil nil nil
+                (and (consp elt) (nth 1 elt))))
+      (goto-char (if (consp elt) (car elt) elt))
+      (if (and (consp elt) (cdr elt)) (backward-char))
+      (copy-tree '(0 nil nil nil nil
+                     nil
+                     0 nil nil nil)))))
 
 (defun c-parse-ps-state-to-cache (state)
   ;; Convert STATE, a `parse-partial-sexp' state valid at POINT, to an element
-  ;; for the `c-state-semi-nonlit-pos-cache' cache.  This is either POINT
-  ;; (when point is not in a literal) or a list (POINT TYPE STARTING-POS),
-  ;; where TYPE is the type of the literal, either 'string, 'c, or 'c++, and
-  ;; STARTING-POS is the starting position of the comment or string.
-  (cond
-   ((nth 3 state)                       ; A string
-    (list (point) (nth 3 state) (nth 8 state)))
-   ((and (nth 4 state)                  ; A comment
-         (not (eq (nth 7 state) 'syntax-table))) ; but not a psuedo comment.
-    (list (point)
-          (if (eq (nth 7 state) 1) 'c++ 'c)
-          (nth 8 state)))
-   (t                                   ; Neither string nor comment.
-    (point))))
+  ;; for the `c-state-semi-nonlit-pos-cache' cache.  This is one of
+  ;;   o - POINT (when point is not in a literal);
+  ;;   o - (POINT CHAR-1) (when the last character before point is potentially
+  ;;       the first of a two-character construct
+  ;;   o - (POINT TYPE STARTING-POS) (when in a literal);
+  ;;   o - (POINT TYPE STARTING-POS CHAR-1) (Combination of the previous two),
+  ;; where TYPE is the type of the literal (either 'c, or 'c++, or the
+  ;; character which closes the string), STARTING-POS is the starting
+  ;; position of the comment or string.  CHAR-1 is either the character
+  ;; potentially forming the first half of a two-char construct (in Emacs <=
+  ;; 25 and XEmacs) or the syntax of the character (in Emacs >= 26).
+  (if (memq 'pps-extended-state c-emacs-features)
+      ;; Emacs >= 26.
+      (let ((basic
+             (cond
+              ((nth 3 state)            ; A string
+               (list (point) (nth 3 state) (nth 8 state)))
+              ((and (nth 4 state)                ; A comment
+                    (not (eq (nth 7 state) 'syntax-table))) ; but not a psuedo comment.
+               (list (point)
+                     (if (eq (nth 7 state) 1) 'c++ 'c)
+                     (nth 8 state)))
+              (t                        ; Neither string nor comment.
+               (point)))))
+        (if (nth 10 state)
+            (append (if (consp basic)
+                        basic
+                      (list basic))
+                    (list (nth 10 state)))
+          basic))
+
+    ;; Emacs <= 25, XEmacs.
+    (cond
+     ((nth 3 state)                     ; A string
+      (if (eq (char-before) ?\\)
+          (list (point) (nth 3 state) (nth 8 state) ?\\)
+        (list (point) (nth 3 state) (nth 8 state))))
+     ((and (nth 4 state)                ; comment
+           (not (eq (nth 7 state) 'syntax-table)))
+      (if (and (eq (char-before) ?*)
+               (> (- (point) (nth 8 state)) 2)) ; not "/*/".
+          (list (point)
+                (if (eq (nth 7 state) 1) 'c++ 'c)
+                (nth 8 state)
+                ?*)
+        (list (point)
+                (if (eq (nth 7 state) 1) 'c++ 'c)
+                (nth 8 state))))
+     (t (if (memq (char-before) '(?/ ?\\))
+            (list (point) (char-before))
+          (point))))))
 
 (defsubst c-ps-state-cache-pos (elt)
   ;; Get the buffer position from ELT, an element from the cache
@@ -2637,7 +2704,7 @@ comment at the start of cc-engine.el for more info."
     (save-restriction
       (widen)
       (let ((c c-state-semi-nonlit-pos-cache)
-            elt state pos npos high-elt)
+            elt state npos high-elt)
         ;; Trim the cache to take account of buffer changes.
         (while (and c (> (c-ps-state-cache-pos (car c))
                          c-state-semi-nonlit-pos-cache-limit))
@@ -2647,29 +2714,27 @@ comment at the start of cc-engine.el for more info."
         (while (and c (> (c-ps-state-cache-pos (car c)) here))
           (setq high-elt (car c))
           (setq c (cdr c)))
-        (setq pos (or (and c (c-ps-state-cache-pos (car c)))
-                      (point-min)))
+        (goto-char (or (and c (c-ps-state-cache-pos (car c)))
+                       (point-min)))
+        (setq state
+              (if c
+                  (c-cache-to-parse-ps-state (car c))
+                (copy-tree '(0 nil nil nil nil nil 0 nil nil nil nil))))
 
-        (if high-elt
-            (setq state (c-cache-to-parse-ps-state (car c)))
-          (setq elt (if c (car c) (point-min)))
-          (setq state
-                (if c
-                    (c-cache-to-parse-ps-state (car c))
-                  (copy-tree '(0 nil nil nil nil nil 0 nil nil nil nil))))
+        (when (not high-elt)
+          ;; We need to extend the cache.  Add an element to
+          ;; `c-state-semi-nonlit-pos-cache' each iteration of the following.
           (while
-              ;; Add an element to `c-state-semi-nonlit-pos-cache' each iteration.
-              (<= (setq npos (+ pos c-state-nonlit-pos-interval)) here)
-            (setq state (parse-partial-sexp pos npos nil nil state))
+              (<= (setq npos (+ (point) c-state-nonlit-pos-interval)) here)
+            (setq state (parse-partial-sexp (point) npos nil nil state))
             (setq elt (c-parse-ps-state-to-cache state))
             (setq c-state-semi-nonlit-pos-cache
-                  (cons elt c-state-semi-nonlit-pos-cache))
-            (setq pos npos)))
+                  (cons elt c-state-semi-nonlit-pos-cache))))
 
-        (if (> pos c-state-semi-nonlit-pos-cache-limit)
-            (setq c-state-semi-nonlit-pos-cache-limit pos))
+        (if (> (point) c-state-semi-nonlit-pos-cache-limit)
+            (setq c-state-semi-nonlit-pos-cache-limit (point)))
 
-        (cons pos state)))))
+        (cons (point) state)))))
 
 (defun c-state-safe-place (here)
   ;; Return a buffer position before HERE which is "safe", i.e. outside any