Support custom categories on root documentation page

When custom categories are used in older versions, raco setup will
report a warning, but the documentation will still appear under the
Miscellaneous section. Thus, this is a backwards compatible
implementation of the idea.

pkgs/racket-doc/scribblings/raco/setup.scrbl

@@ -452,9 +452,13 @@ Optional @filepath{info.rkt} fields trigger additional actions by
     ]
 
     The @racket[_category] list specifies how to show the document in
-    the root table of contents. The list must start with a symbol,
+    the root table of contents. The list must start with a category,
-    usually one of the following categories, which are ordered as
+    which determines where the manual appears in the root
-    below in the root documentation page:
+    documentation page. A category is either a string or a symbol. If
+    it is a string, then the string is the category label on the root
+    page. If it is a symbol, then it a default category label is
+    used. The available symbols and the order of categories on the
+    root documentation page is as below:
 
    @itemize[
 
@@ -483,6 +487,8 @@ Optional @filepath{info.rkt} fields trigger additional actions by
      @item{@racket['interop] : Documentation for interoperability
            tools and libraries.}
 
+     @item{All string categories as ordered by @racket[string<=?].}
+     
      @item{@racket['library] : Documentation for libraries; this
            category is the default and used for unrecognized category
            symbols.}

pkgs/racket-index/scribblings/main/private/manuals.rkt

@@ -28,7 +28,7 @@
                                       (truncate (/ (caar l) 10))))])
                     (if sep? (cons (mk-sep lbl) l) l))]))))
 
-(define (get-docs all? tag)
+(define (get-docs all? tag #:custom-secs [custom-secs (make-hash)])
   (let* ([recs (find-relevant-directory-records (list tag) (if all? 'all-available 'no-user))]
          [infos (map get-info/full (map directory-record-path recs))]
          [docs (append-map
@@ -55,7 +55,10 @@
                             ;; Category
                             (let ([the-cat
                                    (if (pair? new-cat) (car new-cat) 'unknown)])
-                              (or (and (or (eq? the-cat 'omit) 
+                              (or (and (string? the-cat)
+                                       (let ([the-cat-sym (gensym)])
+                                         (hash-ref! custom-secs the-cat the-cat-sym)))
+                                  (and (or (eq? the-cat 'omit) 
                                            (eq? the-cat 'omit-start))
                                        the-cat)
                                   (ormap (lambda (sec)
@@ -90,7 +93,18 @@
       (cdr l)))
 
 (define (make-start-page all?)
-  (let* ([docs (get-docs all? 'scribblings)]
+  (let* ([custom-secs (make-hash)]
+         [docs (get-docs all? 'scribblings
+                         #:custom-secs custom-secs)]
+         [sections+custom
+          (append-map (λ (sec)
+                        (if (eq? 'library (sec-cat sec))
+                            (append (for/list ([label (sort (hash-keys custom-secs)
+                                                            string<=?)])
+                                      (make-sec (hash-ref custom-secs label) label))
+                                    (list sec))
+                            (list sec)))
+                      sections)]
          [plain-line
           (lambda content
             (list (make-flow (list (make-paragraph content)))))]
@@ -151,5 +165,5 @@
                                                 renderer part resolve-info))])
                                     (string-ci<? (str ad) (str bd)))
                                   (> (car ad) (car bd)))))))])))
-         sections))))
+         sections+custom))))
     (make-delayed-block contents)))

pkgs/racket-index/setup/scribble.rkt

@@ -162,7 +162,8 @@
            (or (not name) (collection-name-element? name))
            (and (list? cat)
                 (<= 1 (length cat) 2)
-                (symbol? (car cat))
+                (or (symbol? (car cat))
+                    (string? (car cat)))
                 (or (null? (cdr cat))
                     (real? (cadr cat))))
            (and (exact-positive-integer? out-count))