compiler/cm-accomplice: adjust protocol for extra options

Instead of introducing a subtype of `file-dependency` to imply one new
option, add a subtype that has an options table for easier
extensibility. (Thanks to Sam for pointing out that I shouldn't make
this mistake again.)

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

@@ -560,16 +560,16 @@ logger named @racket['cm-accomplice]. The message data is a
 the first field's value is @racket[file] and the second field's value
 is @racket[#f] (to indicate a non-module dependency). If the
 @racket[indirect?] argument is true, the data is more specifically an
-instance of a @racketidfont{file-dependency/indirect} prefab structure
-type that is a subtype of @racketidfont{file-dependency} with no new
-fields.
+instance of a @racketidfont{file-dependency/options} prefab structure
+type that is a subtype of @racketidfont{file-dependency} with one extra
+field: a hash table mapping @racket['indirect] to @racket[#t].
 
 A compilation manager implemented by @racketmodname[compiler/cm] looks
 for such messages to register an external dependency. In response, the
 compilation manager records (in a @filepath{.dep} file) the path as
 contributing to the implementation of the module currently being
 compiled. Afterward, if the registered file is modified, the
-compilation manager will know to recompile the module. An ``indirect''
+compilation manager will know to recompile the module. An indirect
 dependency has no effect on recompilation, but it can signal to other
 tools, such as a package-dependency checker, that the dependency is
 indirect (and should not imply a direct package dependency).

racket/collects/compiler/cm-accomplice.rkt

@@ -16,5 +16,6 @@
                'cm-accomplice
                (format "file dependency: ~s" f)
                (if indirect?
-                   `#s((file-dependency/indirect file-dependency 2) ,f ,module?)
+                   `#s((file-dependency/options file-dependency 2) ,f ,module?
+                       #hasheq((indirect . #t)))
                    `#s(file-dependency ,f ,module?))))

racket/collects/compiler/cm.rkt

@@ -317,7 +317,7 @@
 (define-struct ext-reader-guard (proc top)
   #:property prop:procedure (struct-field-index proc))
 (define-struct file-dependency (path module?) #:prefab)
-(define-struct (file-dependency/indirect file-dependency) () #:prefab)
+(define-struct (file-dependency/options file-dependency) (table) #:prefab)
 
 (define (compile-zo* mode roots path src-sha1 read-src-syntax zo-name up-to-date collection-cache)
   ;; The `path' argument has been converted to .rkt or .ss form,
@@ -398,7 +398,10 @@
                    (path? (file-dependency-path (vector-ref l 2))))
           (external-dep! (file-dependency-path (vector-ref l 2))
                          (file-dependency-module? (vector-ref l 2))
-                         (file-dependency/indirect? (vector-ref l 2))))
+                         (and (file-dependency/options? (vector-ref l 2))
+                              (hash-ref (file-dependency/options-table (vector-ref l 2))
+                                        'indirect
+                                        #f))))
         (loop))))
 
   ;; Write the code and dependencies: