+(defvar find-function-C-source-directory
+ (let ((dir (expand-file-name "src" source-directory)))
+ (when (and (file-directory-p dir) (file-readable-p dir))
+ dir))
+ "Directory where the C source files of Emacs can be found.
+If nil, do not try to find the source code of functions and variables
+defined in C.")
+
+(defun find-function-C-source (fun-or-var file variable-p)
+ "Find the source location where SUBR-OR-VAR is defined in FILE.
+VARIABLE-P should be non-nil for a variable or nil for a subroutine."
+ (unless find-function-C-source-directory
+ (setq find-function-C-source-directory
+ (read-directory-name "Emacs C source dir: " nil nil t)))
+ (setq file (expand-file-name file find-function-C-source-directory))
+ (unless (file-readable-p file)
+ (error "The C source file %s is not available"
+ (file-name-nondirectory file)))
+ (unless variable-p
+ (setq fun-or-var (indirect-function fun-or-var)))
+ (with-current-buffer (find-file-noselect file)
+ (goto-char (point-min))
+ (unless (re-search-forward
+ (if variable-p
+ (concat "DEFVAR[A-Z_]*[ \t\n]*([ \t\n]*\""
+ (regexp-quote (symbol-name fun-or-var))
+ "\"")
+ (concat "DEFUN[ \t\n]*([ \t\n]*\""
+ (regexp-quote (subr-name fun-or-var))
+ "\""))
+ nil t)
+ (error "Can't find source for %s" fun-or-var))
+ (cons (current-buffer) (match-beginning 0))))
+