Use "G_" as the conventional alias for gettext

Since the change in 2.2 noted in the NEWS as "Fix literal matching for
module-bound literals", defining `_' makes `syntax-rules' and `match'
fail to recognize `_' as the catch-all literal.  This change adapts the
recommendations to current practice in 2.2, as users have had to adapt
to this change.

* doc/ref/api-i18n.texi (Gettext Support): Update documentation.
* module/language/tree-il/analyze.scm (proc-ref?, gettext?): G_ is the
  conventional abbreviation, not _.
* test-suite/tests/tree-il.test: Adapt.
* module/ice-9/command-line.scm: Use G_ instead of _.

module/ice-9/command-line.scm

@@ -40,15 +40,15 @@
             emit-bug-reporting-address))
 
 ;; An initial stab at i18n.
-(define _ gettext)
+(define G_ gettext)
 
 (define *GPLv3+*
-  (_ "License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
+  (G_ "License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
 This is free software: you are free to change and redistribute it.
 There is NO WARRANTY, to the extent permitted by law."))
 
 (define *LGPLv3+*
-  (_ "License LGPLv3+: GNU LGPL 3 or later <http://gnu.org/licenses/lgpl.html>.
+  (G_ "License LGPLv3+: GNU LGPL 3 or later <http://gnu.org/licenses/lgpl.html>.
 This is free software: you are free to change and redistribute it.
 There is NO WARRANTY, to the extent permitted by law."))
 
@@ -79,8 +79,8 @@ There is NO WARRANTY, to the extent permitted by law."))
 
   (if packager
       (if packager-version
-          (format port (_ "Packaged by ~a (~a)\n") packager packager-version)
-          (format port (_ "Packaged by ~a\n") packager)))
+          (format port (G_ "Packaged by ~a (~a)\n") packager packager-version)
+          (format port (G_ "Packaged by ~a\n") packager)))
   
   (display copyright port)
   (newline port)
@@ -98,15 +98,15 @@ There is NO WARRANTY, to the extent permitted by law."))
                                            package
                                            "/"))
                                      packager packager-bug-address)
-  (format port (_ "\nReport bugs to: ~a\n") bug-address)
+  (format port (G_ "\nReport bugs to: ~a\n") bug-address)
   (if (and packager packager-bug-address)
-      (format port (_ "Report ~a bugs to: ~a\n") packager packager-bug-address))
-  (format port (_ "~a home page: <~a>\n") package url)
+      (format port (G_ "Report ~a bugs to: ~a\n") packager packager-bug-address))
+  (format port (G_ "~a home page: <~a>\n") package url)
   (format port
-          (_ "General help using GNU software: <http://www.gnu.org/gethelp/>\n")))
+          (G_ "General help using GNU software: <http://www.gnu.org/gethelp/>\n")))
 
 (define *usage*
-  (_ "Evaluate code with Guile, interactively or from a script.
+  (G_ "Evaluate code with Guile, interactively or from a script.
 
   [-s] FILE      load source code from FILE, and exit
   -c EXPR        evalute expression EXPR, and exit
@@ -151,7 +151,7 @@ If FILE begins with `-' the -s switch is mandatory.
       (apply format port fmt args)
       (newline port))
 
-    (format port (_ "Usage: ~a [OPTION]... [FILE]...\n") name)
+    (format port (G_ "Usage: ~a [OPTION]... [FILE]...\n") name)
     (display *usage* port)
     (newline port)
 

module/language/tree-il/analyze.scm

@@ -1,6 +1,6 @@
 ;;; TREE-IL -> GLIL compiler
 
-;; Copyright (C) 2001, 2008-2014, 2018 Free Software Foundation, Inc.
+;; Copyright (C) 2001,2008-2014,2016,2018-2019 Free Software Foundation, Inc.
 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -1422,7 +1422,7 @@ resort, return #t when EXP refers to the global variable SPECIAL-NAME."
 
   (match exp
     (($ <toplevel-ref> _ _ (? special?))
-     ;; Allow top-levels like: (define _ (cut gettext <> "my-domain")).
+     ;; Allow top-levels like: (define G_ (cut gettext <> "my-domain")).
      #t)
     (($ <toplevel-ref> _ _ name)
      (let ((var (module-variable env name)))
@@ -1440,7 +1440,7 @@ resort, return #t when EXP refers to the global variable SPECIAL-NAME."
      #t)
     (_ #f)))
 
-(define gettext? (cut proc-ref? <> gettext '_ <>))
+(define gettext? (cut proc-ref? <> gettext 'G_ <>))
 (define ngettext? (cut proc-ref? <> ngettext 'N_ <>))
 
 (define (const-fmt x env)
@@ -1450,7 +1450,7 @@ resort, return #t when EXP refers to the global variable SPECIAL-NAME."
      exp)
     (($ <call> _ (? (cut gettext? <> env))
         (($ <const> _ (? string? fmt))))
-     ;; Gettexted literals, like `(_ "foo")'.
+     ;; Gettexted literals, like `(G_ "foo")'.
      fmt)
     (($ <call> _ (? (cut ngettext? <> env))
         (($ <const> _ (? string? fmt)) ($ <const> _ (? string?)) _ ..1))