deprecate omission of port to ice-9 format

* module/ice-9/format.scm (format): Add port and format-string as formal
  arguments. Seems also to have triggered a reindent.  Formally
  deprecate omitting the port, as it's usually an error.

* test-suite/tests/format.test ("format basic output")
  ("format basic output", "~{ iteration"): Fix up tests that omitted the
  destination port.

module/ice-9/format.scm

@@ -44,7 +44,7 @@
 
 ;;; End of configuration ----------------------------------------------------
 
-(define (format . args)
+(define (format port format-string . args)
   (define format:version "3.0")
   (define format:port #f)            ; curr. format output port
   (define format:output-col 0)       ; curr. format output tty column
@@ -1645,7 +1645,26 @@
   (set! format:fn-str (make-string format:fn-max)) ; number buffer
   (set! format:en-str (make-string format:en-max)) ; exponent buffer
 
-  (apply format:format args))
+  (apply format:format port format-string args))
+
+(begin-deprecated
+ (set! format
+       (let ((format format))
+         (case-lambda
+           ((port format-string . args)
+            (if (string? port)
+                (begin
+                  (issue-deprecation-warning
+                   "Omitting the destination port on a call to format is deprecated."
+                   "Pass #f as the destination port, before the format string.")
+                  (apply format #f port format-string args))
+                (apply format port format-string args)))
+           ((deprecated-format-string-only)
+            (issue-deprecation-warning
+             "Omitting the destination port on a call to format is deprecated."
+             "Pass #f as the destination port, before the format string.")
+            (format #f deprecated-format-string-only))))))
+
 
 ;; Thanks to Shuji Narazaki
 (module-set! the-root-module 'format format)

test-suite/tests/format.test

@@ -26,9 +26,9 @@
 
 (with-test-prefix "format basic output"
   (pass-if "format ~% produces a new line"
-	   (string=? (format "~%") "\n"))
+	   (string=? (format #f "~%") "\n"))
   (pass-if "format ~& starts a fresh line"
-	   (string=? (format "~&abc~&~&") "abc\n"))
+	   (string=? (format #f "~&abc~&~&") "abc\n"))
   (pass-if "format ~& is stateless but works properly across outputs via port-column"
 	   (string=?
 	    (with-output-to-string
@@ -39,7 +39,7 @@
 		(format #t "~&~&")))
 	    "xyz\nabc\n"))
   (pass-if "format ~F (format-out-substr) maintains the column correctly"
-	   (= (string-length (format "~@F~20T" 1)) 20)))
+	   (= (string-length (format #f "~@F~20T" 1)) 20)))
 
 ;;;
 ;;; misc
@@ -99,4 +99,4 @@
   ;; In Guile 1.6.4 and earlier, the maximum iterations parameter defaulted
   ;; to 100, but it's now like Common Lisp where the default is no limit
   (pass-if "no arbitrary iteration limit"
-    (= (string-length (format "~{~a~}" (make-list 200 #\b))) 200)))
+    (= (string-length (format #f "~{~a~}" (make-list 200 #\b))) 200)))