Fix @ and @@ to not capture lexicals; new @@ @@ form for R6RS libraries

* module/ice-9/psyntax.scm (@): Return top-wrap instead of the wrap
  applied to the '@' form, so that the symbol will be interpreted as a
  top-level identifier and never refer to any lexical variable.

  (@@): Change the syntax used to support R6RS 'library' forms to:
  (@@ @@ (mod ...) body).  Change the behavior of the documented
  (@@ (mod ...) id) form to be the same as that of @, except for the use
  of 'private' instead of 'public' in the psyntax mod: use syntax->datum
  on the identifier, and return top-wrap instead of the wrap applied to
  the '@@' form.

  This fixes <http://bugs.gnu.org/10756> reported by Ludovic Courtès.

* module/ice-9/psyntax-pp.scm: Regenerate.

* module/ice-9/r6rs-libraries.scm (library): Use '@@ @@' syntax instead
  of the older '@@' syntax.

* test-suite/tests/syncase.test (changes to expansion environment): Use
  '@@ @@' syntax.

* module/Makefile.am: Add explicit dependencies for boot-9.go on the
  files that it includes: quasisyntax.scm and r6rs-libraries.scm.

module/Makefile.am

@@ -32,6 +32,8 @@ nobase_ccache_DATA += ice-9/eval.go
 EXTRA_DIST += ice-9/eval.scm
 ETAGS_ARGS += ice-9/eval.scm
 
+ice-9/boot-9.go: ice-9/boot-9.scm ice-9/quasisyntax.scm ice-9/r6rs-libraries.scm
+
 # We can compile these in any order, but it's fastest if we compile
 # psyntax and boot-9 first, then the compiler itself, then the rest of
 # the code.

module/ice-9/psyntax-pp.scm

@@ -1950,7 +1950,7 @@
                    (values
                      (syntax->datum id)
                      r
-                     w
+                     '((top))
                      #f
                      (syntax->datum
                        (cons '#(syntax-object public ((top)) (hygiene guile)) mod))))
@@ -1982,6 +1982,22 @@
                             (loop (+ i 1)))))))
                    (else x)))))
         (let* ((tmp-1 e) (tmp ($sc-dispatch tmp-1 '(_ each-any any))))
+          (if (and tmp
+                   (apply (lambda (mod id) (and (and-map id? mod) (id? id))) tmp))
+            (apply (lambda (mod id)
+                     (values
+                       (syntax->datum id)
+                       r
+                       '((top))
+                       #f
+                       (syntax->datum
+                         (cons '#(syntax-object private ((top)) (hygiene guile)) mod))))
+                   tmp)
+            (let ((tmp ($sc-dispatch
+                         tmp-1
+                         '(_ #(free-id #(syntax-object @@ ((top)) (hygiene guile)))
+                             each-any
+                             any))))
               (if (and tmp (apply (lambda (mod exp) (and-map id? mod)) tmp))
                 (apply (lambda (mod exp)
                          (let ((mod (syntax->datum
@@ -1991,7 +2007,7 @@
                 (syntax-violation
                   #f
                   "source expression failed to match any pattern"
-              tmp-1))))))
+                  tmp-1))))))))
   (global-extend
     'core
     'if

module/ice-9/psyntax.scm

@@ -2239,7 +2239,9 @@
                      (syntax-case e ()
                        ((_ (mod ...) id)
                         (and (and-map id? #'(mod ...)) (id? #'id))
-                        (values (syntax->datum #'id) r w #f
+                        ;; Strip the wrap from the identifier and return top-wrap
+                        ;; so that the identifier will not be captured by lexicals.
+                        (values (syntax->datum #'id) r top-wrap #f
                                 (syntax->datum
                                  #'(public mod ...)))))))
 
@@ -2262,9 +2264,20 @@
                                       ((fx= i n) v)
                                     (vector-set! v i (remodulate (vector-ref x i) mod)))))
                                (else x))))
-                     (syntax-case e ()
+                     (syntax-case e (@@)
-                       ((_ (mod ...) exp)
+                       ((_ (mod ...) id)
+                        (and (and-map id? #'(mod ...)) (id? #'id))
+                        ;; Strip the wrap from the identifier and return top-wrap
+                        ;; so that the identifier will not be captured by lexicals.
+                        (values (syntax->datum #'id) r top-wrap #f
+                                (syntax->datum
+                                 #'(private mod ...))))
+                       ((_ @@ (mod ...) exp)
                         (and-map id? #'(mod ...))
+                        ;; This is a special syntax used to support R6RS library forms.
+                        ;; Unlike the syntax above, the last item is not restricted to
+                        ;; be a single identifier, and the syntax objects are kept
+                        ;; intact, with only their module changed.
                         (let ((mod (syntax->datum #'(private mod ...))))
                           (values (remodulate #'exp mod)
                                   r w (source-annotation #'exp)

module/ice-9/r6rs-libraries.scm

@@ -197,7 +197,7 @@
                  (export e ...)
                  (re-export r ...)
                  (export! x ...)
-                 (@@ (name name* ...) body)
+                 (@@ @@ (name name* ...) body)
                  ...))))))))
     
 (define-syntax import

test-suite/tests/syncase.test

@@ -115,15 +115,15 @@
          'foo)))
 
 (with-test-prefix "changes to expansion environment"
-  (pass-if "expander detects changes to current-module with @@"
+  (pass-if "expander detects changes to current-module with @@ @@"
     (compile '(begin
                 (define-module (new-module))
-                (@@ (new-module)
+                (@@ @@ (new-module)
                        (define-syntax new-module-macro
                          (lambda (stx)
                            (syntax-case stx () 
                              ((_ arg) (syntax arg))))))
-                (@@ (new-module)
+                (@@ @@ (new-module)
                        (new-module-macro #t)))
              #:env (current-module))))