[PATCH 2] Add support for C++ headers to `ffap'.

["Rüdiger Sonderfeld" <ruediger@c-plusplus.de>]

This updated version also checks if GCC was configured with
`--with-gxx-include-dir='.

--- 8< ------------------------------------------------------------- >8 ---

Using only `ffap-c-mode' does not work for C++ headers from
libstdc++.  Those headers are usually stored in
"/usr/include/c++/<version>/".

* lisp/ffap.el (ffap-c++-path): New variable.
(ffap-c++-mode): New function.
(ffap-alist): Use `ffap-c++-mode' for `c++-mode'.

Signed-off-by: Rüdiger Sonderfeld <ruediger@c-plusplus.de>
---
 lisp/ffap.el | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/lisp/ffap.el b/lisp/ffap.el
index 737de8b..79539a4 100644
--- a/lisp/ffap.el
+++ b/lisp/ffap.el
@@ -769,7 +769,7 @@ (defvar ffap-alist
     ;; (lisp-interaction-mode . ffap-el-mode) ; maybe
     (finder-mode . ffap-el-mode)	; type {C-h p} and try it
     (help-mode . ffap-el-mode)		; maybe useful
-    (c++-mode . ffap-c-mode)		; search ffap-c-path
+    (c++-mode . ffap-c++-mode)		; search ffap-c++-path
     (cc-mode . ffap-c-mode)		; same
     ("\\.\\([chCH]\\|cc\\|hh\\)\\'" . ffap-c-mode) ; stdio.h
     (fortran-mode . ffap-fortran-mode)	; FORTRAN requested by MDB
@@ -866,6 +866,28 @@ (defvar ffap-c-path
 (defun ffap-c-mode (name)
   (ffap-locate-file name t ffap-c-path))
 
+(defvar ffap-c++-path
+  (let ((c++-include-dir (with-temp-buffer
+                           (when (eq 0 (ignore-errors
+                                         (call-process "g++" nil t nil "-v")))
+                             (goto-char (point-min))
+                             (if (re-search-forward "--with-gxx-include-dir=\
+\\([^[:space:]]+\\)"
+                                                      nil 'noerror)
+                                 (match-string 1)
+                               (when (re-search-forward "gcc version \
+\\([[:digit:]]+.[[:digit:]]+.[[:digit:]]+\\)"
+                                                   nil 'noerror)
+                                 (expand-file-name (match-string 1)
+                                                   "/usr/include/c++/")))))))
+    (if c++-include-dir
+        (cons c++-include-dir ffap-c-path)
+      ffap-c-path))
+  "List of directories to search for include files.")
+
+(defun ffap-c++-mode (name)
+  (ffap-locate-file name t ffap-c++-path))
+
 (defvar ffap-fortran-path '("../include" "/usr/include"))
 
 (defun ffap-fortran-mode (name)
-- 
1.8.4