Update match's no-matching-pattern code to use "throw"

* module/ice-9/match.upstream.scm (match-next): Use throw, so that CPS
  can see that there's no fallthrough.
* module/ice-9/match.scm: Add a note about what to do in 3.1 to remove
  the old "error" definition.

module/ice-9/match.scm

@@ -1,6 +1,6 @@
 ;;; -*- mode: scheme; coding: utf-8; -*-
 ;;;
-;;; Copyright (C) 2010, 2011, 2012 Free Software Foundation, Inc.
+;;; Copyright (C) 2010, 2011, 2012, 2020 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
@@ -24,12 +24,16 @@
             match-let*
             match-letrec))
 
-(define (error _ . args)
-  ;; Error procedure for run-time "no matching pattern" errors.
-  (apply throw 'match-error "match" args))
-
 ;; Support for record matching.
 
+;; For backwards compatibility with previously-compiled files, keep the
+;; old definition of "error" around.
+(define (error _ . args)
+  (apply throw 'match-error "match" args))
+;; FIXME: In 3.1.x, use this new definition:
+;; (define-syntax-rule (error where msg datum)
+;;   (throw 'match-error "match" msg datum))
+
 (define-syntax slot-ref
   (syntax-rules ()
     ((_ rtd rec n)

module/ice-9/match.upstream.scm

@@ -292,7 +292,7 @@
      ;; Here we call error in non-tail context, so that the backtrace
      ;; can show the source location of the failing match form.
      (begin
-       (error 'match "no matching pattern" v)
+       (throw 'match-error "match" "no matching pattern" v)
        #f))
     ;; named failure continuation
     ((match-next v g+s (pat (=> failure) . body) . rest)