bug#43179: CC Mode 5.33.2 (C/*l); (forward-comment -1) doesn't move

[Norrish, Michael (Data61, Acton)]

In this file (between the hyphens):

----- 
int x = 4;
/*
(Assume all positive) */

int y;
-----

Put the cursor immediately after the comment.

Then eval (forward-comment -1)

Rather than jumping to the start of line 2, the cursor stays where it
is.

If the comment is merged to all be on one line, the movement works as I
expected.

Michael


Package: cc-mode

Emacs  : GNU Emacs 26.3 (build 1, x86_64-apple-darwin18.2.0, NS appkit-1671.20 
Version 10.14.3 (Build 18D109))
 of 2019-09-02
Package: CC Mode 5.33.2 (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)

current state:
==============
(setq
 c-basic-offset 2
 c-comment-only-line-offset '(0 . 0)
 c-indent-comment-alist '((anchored-comment column . 0) (end-block space . 1)
                          (cpp-end-block space . 2))
 c-indent-comments-syntactically-p nil
 c-block-comment-prefix ""
 c-comment-prefix-regexp '((pike-mode . "//+!?\\|\\**") (awk-mode . "#+")
                           (other . "//+\\|\\**"))
 c-doc-comment-style '((java-mode . javadoc) (pike-mode . autodoc)
                       (c-mode . gtkdoc))
 c-cleanup-list '(scope-operator)
 c-hanging-braces-alist '((substatement-open before after)
                          (arglist-cont-nonempty))
 c-hanging-colons-alist nil
 c-hanging-semi&comma-criteria '(c-semi&comma-inside-parenlist)
 c-backslash-column 48
 c-backslash-max-column 72
 c-special-indent-hook '(c-gnu-impose-minimum)
 c-label-minimum-indentation 1
 c-offsets-alist '((inexpr-class . +)
                   (inexpr-statement . +)
                   (lambda-intro-cont . +)
                   (inlambda . c-lineup-inexpr-block)
                   (template-args-cont c-lineup-template-args +)
                   (incomposition . +)
                   (inmodule . +)
                   (innamespace . +)
                   (inextern-lang . +)
                   (composition-close . 0)
                   (module-close . 0)
                   (namespace-close . 0)
                   (extern-lang-close . 0)
                   (composition-open . 0)
                   (module-open . 0)
                   (namespace-open . 0)
                   (extern-lang-open . 0)
                   (objc-method-call-cont
                    c-lineup-ObjC-method-call-colons
                    c-lineup-ObjC-method-call
                    +
                    )
                   (objc-method-args-cont . c-lineup-ObjC-method-args)
                   (objc-method-intro . [0])
                   (friend . 0)
                   (cpp-define-intro c-lineup-cpp-define +)
                   (cpp-macro-cont . +)
                   (cpp-macro . [0])
                   (inclass . +)
                   (stream-op . c-lineup-streamop)
                   (arglist-cont-nonempty
                    c-lineup-gcc-asm-reg
                    c-lineup-arglist
                    )
                   (arglist-cont c-lineup-gcc-asm-reg 0)
                   (comment-intro
                    c-lineup-knr-region-comment
                    c-lineup-comment
                    )
                   (catch-clause . 0)
                   (else-clause . 0)
                   (do-while-closure . 0)
                   (access-label . -)
                   (case-label . 0)
                   (substatement . +)
                   (statement-case-intro . +)
                   (statement . 0)
                   (brace-entry-open . 0)
                   (brace-list-entry . c-lineup-under-anchor)
                   (brace-list-close . 0)
                   (block-close . 0)
                   (block-open . 0)
                   (inher-cont . c-lineup-multi-inher)
                   (inher-intro . +)
                   (member-init-cont . c-lineup-multi-inher)
                   (member-init-intro . +)
                   (annotation-var-cont . +)
                   (annotation-top-cont . 0)
                   (topmost-intro . 0)
                   (knr-argdecl . 0)
                   (func-decl-cont . +)
                   (inline-close . 0)
                   (class-close . 0)
                   (class-open . 0)
                   (defun-block-intro . +)
                   (defun-close . 0)
                   (defun-open . 0)
                   (c . c-lineup-C-comments)
                   (string . c-lineup-dont-change)
                   (topmost-intro-cont
                    first
                    c-lineup-topmost-intro-cont
                    c-lineup-gnu-DEFUN-intro-cont
                    )
                   (brace-list-intro . c-lineup-arglist-intro-after-paren)
                   (brace-list-open . +)
                   (inline-open . 0)
                   (arglist-close . c-lineup-arglist)
                   (arglist-intro . c-lineup-arglist-intro-after-paren)
                   (statement-cont . +)
                   (statement-case-open . +)
                   (label . 0)
                   (substatement-label . 0)
                   (substatement-open . +)
                   (knr-argdecl-intro . 5)
                   (statement-block-intro . +)
                   )
 c-buffer-is-cc-mode 'c-mode
 c-tab-always-indent t
 c-syntactic-indentation t
 c-syntactic-indentation-in-macros t
 c-ignore-auto-fill '(string cpp code)
 c-auto-align-backslashes t
 c-backspace-function 'backward-delete-char-untabify
 c-delete-function 'delete-char
 c-electric-pound-behavior nil
 c-default-style '((java-mode . "java") (awk-mode . "awk") (other . "gnu"))
 c-enable-xemacs-performance-kludge-p nil
 c-old-style-variable-behavior nil
 defun-prompt-regexp nil
 tab-width 8
 comment-column 32
 parse-sexp-ignore-comments t
 parse-sexp-lookup-properties t
 auto-fill-function nil
 comment-multi-line t
 comment-start-skip "\\(//+\\|/\\*+\\)\\s *"
 fill-prefix nil
 fill-column 70
 paragraph-start "[     ]*\\(//+\\|\\**\\)[     ]*$\\|^\f"
 adaptive-fill-mode t
 adaptive-fill-regexp "[        ]*\\(//+\\|\\**\\)[     ]*\\([  
]*\\([-–!|#%;>*·•‣⁃◦]+[         ]*\\)*\\)"
 )