allow empty splicing-syntax-parameterize body in a defn context (PR 10311)

svn: r15251

collects/scheme/private/stxparam.ss

@@ -11,9 +11,9 @@
 
   (#%provide (for-syntax do-syntax-parameterize))
 
-  (define-for-syntax (do-syntax-parameterize stx let-syntaxes-id)
+  (define-for-syntax (do-syntax-parameterize stx let-syntaxes-id empty-body-ok?)
     (syntax-case stx ()
-      [(_ ([id val] ...) body0 body ...)
+      [(_ ([id val] ...) body ...)
        (let ([ids (syntax->list #'(id ...))])
 	 (with-syntax ([(gen-id ...)
 			(map (lambda (id)
@@ -43,7 +43,13 @@
 		"duplicate binding"
 		stx
 		dup)))
+           (unless empty-body-ok?
+             (when (null? (syntax-e #'(body ...)))
+               (raise-syntax-error
+                #f
+                "missing body expression(s)"
+                stx)))
            (with-syntax ([let-syntaxes let-syntaxes-id])
              (syntax/loc stx
                (let-syntaxes ([(gen-id) (convert-renamer val)] ...)
-                 body0 body ...)))))])))
+                 body ...)))))])))

collects/scheme/splicing.ss

@@ -169,9 +169,9 @@
 (define-syntax (splicing-syntax-parameterize stx)
   (if (eq? 'expression (syntax-local-context))
       ;; Splicing is no help in an expression context:
-      (do-syntax-parameterize stx #'let-syntaxes)
+      (do-syntax-parameterize stx #'let-syntaxes #f)
       ;; Let `syntax-parameterize' check syntax, then continue
-      (do-syntax-parameterize stx #'ssp-let-syntaxes)))
+      (do-syntax-parameterize stx #'ssp-let-syntaxes #t)))
 
 (define-syntax (ssp-let-syntaxes stx)
   (syntax-case stx ()

collects/scheme/stxparam.ss

@@ -31,4 +31,4 @@
 		   gen-id))))))]))
 
   (define-syntax (syntax-parameterize stx)
-    (do-syntax-parameterize stx #'let-syntaxes)))
+    (do-syntax-parameterize stx #'let-syntaxes #f)))

collects/scribblings/reference/splicing.scrbl

@@ -66,7 +66,8 @@ forms are valid in an internal-definition context. In particular,
 @scheme[require] and @scheme[provide] forms cannot appear in the body
 of @scheme[splicing-syntax-parameterize], even if
 @scheme[splicing-syntax-parameterize] is used in a @scheme[module]
-body.
+body. In a definition context, the body of
+@scheme[splicing-syntax-parameterize] can be empty.
 
 @examples[
 #:eval splice-eval