adjust section counting when 'grouper and 'unnumbered are mixed

I'm not certain that mixing 'grouper and non-'grouper parts at a given
level makes sense. Still, this adjustment brings Scribble section
counting more in line with Latex, so that section links are less
likely to have the wrong number label.

scribble-lib/scribble/base-render.rkt

@@ -606,17 +606,28 @@
                                               number))
                                     sub-pos
                                     sub-numberers))
+                    (define unnumbered-and-unnumbered-subsections?
+                      (and (not sub-grouper?)
+                           ;; If this section wasn't marked with
+                           ;; 'grouper but is unnumbered and doesn't
+                           ;; have numbered subsections, then didn't
+                           ;; reset counters, so propagate the old
+                           ;; position
+                           (and unnumbered?
+                                (= next-sub-pos sub-pos))))
                     (loop (cdr parts)
                           (if (or unnumbered? numberer)
                               pos
                               (add1 pos))
                           next-numberers
-                          (if sub-grouper?
-                              next-sub-pos
-                              1)
-                          (if sub-grouper?
-                              next-sub-numberers
-                              #hash())))))))
+                          (cond
+                            [sub-grouper? next-sub-pos]
+                            [unnumbered-and-unnumbered-subsections? sub-pos]
+                            [else 1])
+                          (cond
+                            [sub-grouper? next-sub-numberers]
+                            [unnumbered-and-unnumbered-subsections? sub-numberers]
+                            [else #hash()])))))))
         (let ([prefix (part-tag-prefix d)])
           (for ([(k v) (collect-info-ht p-ci)])
             (when (cadr k)

scribble-test/tests/scribble/docs/grouper2.scrbl

@@ -0,0 +1,29 @@
+#lang scribble/base
+
+@title{Example}
+
+@table-of-contents[]
+
+@; ----------------------------------------
+
+@section[#:style 'grouper]{Arbitrarily Small Data}
+
+@subsection[#:tag "A"]{A}
+
+See @secref["A"] and @secref["B"].
+
+@; ----------------------------------------
+
+@section[#:style '(unnumbered)]{Intermezzo}
+
+@subsection[#:style '(unnumbered)]{More}
+
+Nothing here.
+
+@; ----------------------------------------
+
+@section[#:style 'grouper]{Arbitrarily Large Data}
+
+@subsection[#:tag "B"]{B}
+
+See @secref["A"] and @secref["B"].

scribble-test/tests/scribble/docs/grouper2.txt

@@ -0,0 +1,28 @@
+Example
+
+    I Arbitrarily Small Data 
+      1 A                    
+                             
+    Intermezzo               
+      More                   
+                             
+    II Arbitrarily Large Data
+      2 B                    
+
+I. Arbitrarily Small Data
+
+1. A
+
+See A and B.
+
+Intermezzo
+
+More
+
+Nothing here.
+
+II. Arbitrarily Large Data
+
+2. B
+
+See A and B.