Allow line comments ending with escaped NL to be continued to the next line.

Use this in C, C++, and Objective C Modes.  Fixes bug#22246

* src/syntax.c (comment-end-can-be-escaped): New buffer local variable.
(forw-comment, back-comment): On encountering an end of comment character,
test whether it is escaped when `comment-end-can-be-escaped' is non-nil.

* doc/lispref/syntax.texi (Control Parsing): Describe
`comment-end-can-be-escaped'.

* etc/NEWS (Lisp Changes): Describe `comment-end-can-be-escaped'.

* lisp/progmodes/cc-langs.el: New c-lang-setvar `comment-end-can-be-escaped'.

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/lispref/syntax.texi b/doc/lispref/syntax.texi
index 7a984e3d87b..831ebd12f55 100644
--- a/doc/lispref/syntax.texi
+++ b/doc/lispref/syntax.texi
@@ -945,6 +945,14 @@ whitespace by the functions in this section and by @code{forward-sexp},
 The behavior of @code{parse-partial-sexp} is also affected by
 @code{parse-sexp-lookup-properties} (@pxref{Syntax Properties}).
 
+@defvar comment-end-can-be-escaped
+If this buffer local variable is non-@code{nil}, a single character
+which usually terminates a comment doesn't do so when that character
+is escaped.  This is used in C and C++ Modes, where line comments
+starting with @samp{//} can be continued onto the next line by
+escaping the newline with @samp{\}.
+@end defvar
+
 You can use @code{forward-comment} to move forward or backward over
 one comment or several comments.