compile: Add '-x' flag.

* module/scripts/compile.scm (%options, compile): Add '-x'.
* doc/ref/api-evaluation.texi (Compilation): Document it.

doc/ref/api-evaluation.texi

@@ -658,6 +658,12 @@ Write output bytecode to @var{ofile}.  By convention, bytecode file
 names end in @code{.go}.  When @option{-o} is omitted, the output file
 name is as for @code{compile-file} (see below).
 
+@item -x @var{extension}
+Recognize @var{extension} as a valid source file name extension.
+
+For example, to compile R6RS code, you might want to pass @command{-x
+.sls} so that files ending in @file{.sls} can be found.
+
 @item -W @var{warning}
 @itemx --warn=@var{warning}
 @cindex warnings, compiler

module/scripts/compile.scm

@@ -1,6 +1,6 @@
 ;;; Compile --- Command-line Guile Scheme compiler  -*- coding: iso-8859-1 -*-
 
-;; Copyright 2005, 2008-2011, 2013, 2014, 2015, 2017 Free Software Foundation, Inc.
+;; Copyright 2005, 2008-2011, 2013-2015, 2017-2018 Free Software Foundation, Inc.
 ;;
 ;; This program is free software; you can redistribute it and/or
 ;; modify it under the terms of the GNU Lesser General Public License
@@ -83,6 +83,10 @@
 		  (if (assoc-ref result 'output-file)
 		      (fail "`-o' option cannot be specified more than once")
 		      (alist-cons 'output-file arg result))))
+        (option '(#\x) #t #f
+                (lambda (opt name arg result)
+                  (set! %load-extensions (cons arg %load-extensions))
+                  result))
 
         (option '(#\W "warn") #t #f
                 (lambda (opt name arg result)
@@ -213,6 +217,7 @@ Compile each Guile source file FILE into a Guile object.
 
   -L, --load-path=DIR  add DIR to the front of the module load path
   -o, --output=OFILE   write output to OFILE
+  -x EXTENSION         add EXTENSION to the set of source file extensions
 
   -W, --warn=WARNING   emit warnings of type WARNING; use `--warn=help'
                        for a list of available warnings