move setup/xref from "scribble-lib" to "racket-index"

The `setup/xref` library conceptually belongs in "racket-index",
and moving the library avoids a cross-package use of a private
module.

Merge to v6.0
(cherry picked from commit d37e910169)

pkgs/games/info.rkt

@@ -14,6 +14,7 @@
                "htdp-lib"
                "math-lib"
                "scribble-lib"
+               "racket-index"
                "sgl"
                "srfi-lib"
                "string-constants-lib"))

pkgs/gui-pkgs/gui-lib/framework/private/text.rkt

@@ -16,8 +16,7 @@
          "coroutine.rkt"
          data/queue)
 
-(require setup/xref
+(require scribble/xref
-         scribble/xref
          scribble/manual-struct)
 
 (import mred^
@@ -4024,8 +4023,15 @@ designates the character that triggers autocompletion
   (let* ([sym->mpi (λ (mp) (module-path-index-resolve (module-path-index-join mp #f)))]
          [manual-mpis (and manuals (map sym->mpi manuals))])
     
-    (unless xref 
+    (unless xref
-      (set! xref (load-collections-xref)))
+      (let ([load-collections-xref
+             ;; Make the dependency on `setup/xref' indirect, so that a
+             ;; GUI does not depend on having documentation installed:
+             (with-handlers ([exn:missing-module? (lambda (exn)
+                                                         (lambda ()
+                                                           (load-xref null)))])
+               (dynamic-require 'setup/xref 'load-collections-xref))])
+        (set! xref (load-collections-xref))))
     
     (let ([ht (make-hash)])
       (for-each

pkgs/plt-services/info.rkt

@@ -6,7 +6,8 @@
 
 (define collection 'multi)
 
-(define deps '(;; "Fake" dependencies to make them included
+(define deps '("racket-index"
+               ;; "Fake" dependencies to make them included
                ;; in a default build:
                "main-distribution-test"
                "distro-build"

pkgs/racket-pkgs/racket-index/setup/scribble.rkt

@@ -3,7 +3,7 @@
 (require setup/getinfo
          setup/dirs
          setup/path-to-relative
-         setup/private/path-utils
+         "private/doc-path.rkt"
          setup/collects
          setup/main-doc
          setup/parallel-do

pkgs/racket-pkgs/racket-index/setup/xref.rkt

@@ -1,12 +1,12 @@
-#lang scheme/base
+#lang racket/base
 
 (require scribble/xref
-         scheme/fasl
+         racket/fasl
-         scheme/path
+         racket/path
          racket/promise
          setup/dirs
          setup/getinfo
-         setup/private/path-utils
+         "private/doc-path.rkt"
          setup/doc-db)
 
 (provide load-collections-xref

pkgs/racket-pkgs/racket-test/info.rkt

@@ -27,7 +27,8 @@
                ;; for random testing:
                "redex-lib"))
 
-(define build-deps '("scheme-lib"
+(define build-deps '("racket-index"
+                     "scheme-lib"
                      "srfi-lite-lib"
                      "base"
                      "data-lib"))

pkgs/scribble-pkgs/scribble-doc/info.rkt

@@ -2,7 +2,8 @@
 
 (define collection 'multi)
 
-(define build-deps '("mzscheme-doc"
+(define build-deps '("racket-index"
+                     "mzscheme-doc"
                      "net-doc"
                      "scheme-lib"
                      "draw-doc"

pkgs/scribble-pkgs/scribble-doc/scribblings/scribble/running.scrbl

@@ -126,6 +126,8 @@ information for all installed documentation, so
 
 renders @filepath{mine.scrbl} to @filepath{mine.html} with
 cross-reference links to the Racket installation's documentation.
+(The @filepath{racket-index} package must be installed to use
+@PFlag{m}/@DPFlag{main-xref-in}.)
 
 The @DPFlag{xref-in} flag loads cross-reference information by calling
 a specified module's function. The @racketmodname[setup/xref] module

pkgs/scribble-pkgs/scribble-lib/info.rkt

@@ -2,7 +2,8 @@
 
 (define collection 'multi)
 
-(define deps '("scheme-lib"
+(define deps '("racket-index"
+               "scheme-lib"
                "base"
                "compatibility-lib"
                "scribble-text-lib"