Remove the `referrer' argument from resources.

This turned out to be a bad idea.  The thing is that some resources need
to be referred to in multiple ways -- for example, different texts in
links of different kinds, or using the URL directly in some cases.  The
existence of `get-resource-path' is a witness for this problem, since it
was used for such cases -- this function is removed as well.

There's no point in trying to generalize this here: instead, go back to
a simpler system where a resource always returns its URL (with an
optional argument to get an absolute URL).  When a `referrer'
functionality is needed, build it on top of that, in a place where it
makes more sense.  (That is, in a specific code for generating content,
where there could be a decision that resources have plain links and also
a very short link for use in navbars.)  Otherwise, it's usually simpler
to just define resources and referrers separately (as different
bindings, the latter uses the former).

collects/scribble/html/resource.rkt

@@ -1,9 +1,9 @@
 #lang racket/base
 
-;; Resources are referrable & renderable objects, (most are html pages)
+;; Resources are renderable & referrable objects, (most are html pages).
 
-;; (resource path renderer referrer) creates and returns a new "resource"
-;; value.  The arguments are:
+;; (resource path renderer) creates and returns a new "resource" value.  The
+;; arguments are:
 ;; - `path': the path of the output file, relative to the working directory,
 ;;   indicating where the resource file should be put at, also corresponding to
 ;;   the URL it will be found at.  It must be a `/'-separated relative string,
@@ -13,18 +13,16 @@
 ;;   for the file to be created as an argument.  This path will be different
 ;;   than the `path' argument because this function is invoked in the target
 ;;   directory.
-;; - `referrer': a function accepting one or more arguments (and possibly
-;;   keywords) that produces a value to be used to refer to this resource
-;;   (using `a', `img', etc).  The first value that will be passed to this
-;;   function will be the actual URL path, which depends on the currently
-;;   rendered page path -- the argument will be relative to it.
-;; The resulting resource value is actually a rendering function that is
-;; similar to the `referrer', except without the first URL argument -- when it
-;; is called, it invokes the `referrer' function with the actual (relativized)
-;; URL.  Creating a resource registers the `renderer' to be executed when
-;; rendering is initiated.  Note that more resources can be created while
-;; rendering; they will also be rendered in turn until no more resources are
-;; created.
+;; The resulting resource value is a function that returns the URL for the
+;; resource.  The function takes in an optional boolean which defaults to #f,
+;; and when #t is given, the result will be an absolute full URL.  Note that
+;; the function can be used as a value for output, which will use it as a thunk
+;; (that renders as the relative URL for the resource).  The default relative
+;; resulting URL is, of course, a value that depends on the currently rendered
+;; resource that uses this value.  Creating a resource registers the `renderer'
+;; to be executed when rendering is initiated by `render-all'.  Note that more
+;; resources can be created while rendering; they will also be rendered in turn
+;; until no more resources are created.
 
 (require scribble/text)
 
@@ -167,7 +165,7 @@
 ;; can be one of: #f (do nothing), 'delete-file (delete if a file exists, error
 ;; if exists as a directory)
 (provide resource)
-(define (resource path0 renderer referrer #:exists [exists 'delete-file])
+(define (resource path0 renderer #:exists [exists 'delete-file])
   (define (bad reason) (error 'resource "bad path, ~a: ~e" reason path0))
   (unless (string? path0) (bad "must be a string"))
   (for ([x (in-list '([#rx"^/" "must be relative"]
@@ -196,7 +194,6 @@
                (parameterize ([rendered-dirpath dirpathlist])
                  (printf "  ~a\n" path)
                  (renderer filename))))))
-  (define (url) (relativize filename dirpathlist (rendered-dirpath)))
   (define absolute-url
     (lazy (define url (relativize filename dirpathlist '()))
           (if (url-roots)
@@ -205,18 +202,13 @@
             ;; construct a `file://' result
             (list* "file://" (current-directory) url))))
   (add-renderer path render)
-  (make-keyword-procedure
-   (lambda (kws kvs . args) (keyword-apply referrer kws kvs (url) args))
-   (case-lambda [(x) (if (and (pair? x) (eq? (car x) get-path))
-                       (if (cdr x) absolute-url (url))
-                       (referrer (url) x))]
-                [args (apply referrer (url) args)])))
-
-;; make it possible to always get the path to a resource
-(provide get-resource-path)
-(define get-path (gensym))
-(define (get-resource-path resource [absolute? #f])
-  (resource (cons get-path absolute?)))
+  (define (url [absolute? #f])
+    ;; be conservative, in case it needs to be extended in the future
+    (case absolute?
+      [(#f) (relativize filename dirpathlist (rendered-dirpath))]
+      [(#t) (force absolute-url)]
+      [else (error 'resource "bad absolute flag value: ~e" absolute?)]))
+  url)
 
 ;; a convenient utility to create renderers from some output function (like
 ;; `output-xml' or `display') and some content