Flatter E2, hence better -print-struct-tree

cpdfmanual.tex

@@ -5202,9 +5202,7 @@ To enable the generation of structure information, we may add \texttt{-draw-stru
 \begin{verbatim}
 $cpdf -print-struct-tree out.pdf
 /StructTreeRoot
-└── 
-    └── /P (1)
-        └──\end{verbatim}
+└── /P (1)\end{verbatim}
 
 \noindent To prevent such automatic tagging, relying only on manual tags, use \texttt{-no-auto-tags}. The effect may be reversed at any point with \texttt{-auto-tags}. Unless told otherwise, Cpdf auto-tags text as paragraphs /P, and images as /Figure.
 
@@ -5229,13 +5227,9 @@ There are two types of tag we can add manually. One kind is used to tag individu
 
 \begin{verbatim}
 /StructTreeRoot
-└── 
-    ├── /H1 (1)
-    │   └── 
-    ├── /P (1)
-    │   └── 
-    └── /P (1)
-        └── 
+├── /H1 (1)
+├── /P (1)
+└── /P (1)
 \end{verbatim}
 
 
@@ -5344,22 +5338,20 @@ We can print an abbreviated form of the structure tree to standard output:
 \begin{framed}
 \begin{verbatim}
 /StructTreeRoot
-└── 
-    └── /Document
-        ├── /Sect
-        │   ├── /P (1)
-        │   │   ├── /Span (1)
-        │   │   └── 
-        │   └── /Figure (1)
-        ├── /Sect
-        │   ├── /H1 (2)
-        │   └── /TOC
-        │       ├── /TOCI
-        │       │   └── /P
-        │       │       └── /Link (2)
-        .       .
-        .       .
-        .
+└── /Document
+    ├── /Sect
+    │   ├── /P (1)
+    │   │   ├── /Span (1)
+    │   └── /Figure (1)
+    ├── /Sect
+    │   ├── /H1 (2)
+    │   └── /TOC
+    │       ├── /TOCI
+    │       │   └── /P
+    │       │       └── /Link (2)
+    .       .
+    .       .
+    .       .
 \end{verbatim}
 \end{framed}
 \end{minipage}

cpdfua.ml

@@ -135,7 +135,9 @@ let read_st_basic pdf =
   | Pdf.Dictionary d ->
       begin match lookup "/StructTreeRoot" d with
       | None -> E2 ("/StructTreeRoot", [], [])
-      | Some st -> E2 ("/StructTreeRoot", [], [read_st_inner pdf st])
+      | Some st ->
+          match read_st_inner pdf st with
+          | E2 (_, a, b) -> E2 ("/StructTreeRoot", a, b)
       end
   | _ -> error "read_st no root"
 
@@ -1577,6 +1579,11 @@ let replace_struct_tree pdf json =
   with
     e -> error (Printf.sprintf "replace_struct_tree: %s" (Printexc.to_string e))
 
+let rec remove_empty = function
+  E2 (n, attrs, cs) ->
+    let cs' = map remove_empty cs in
+      E2 (n, attrs, lose (function E2 ("", _, []) -> true | _ -> false) cs')
+
 let print_struct_tree pdf =
   let page_lookup =
     hashtable_of_dictionary (combine (Pdf.page_reference_numbers pdf) (ilist 1 (Pdfpage.endpage pdf)))
@@ -1592,7 +1599,7 @@ let print_struct_tree pdf =
           (Cpdfprinttree.to_string
             ~get_name:(fun (E2 (x, a, _)) -> if int_of_string (get_page a) > 0 then x ^ " (" ^ get_page a ^ ")" else x)
             ~get_children:(fun (E2 (_, _, cs)) -> cs)
-            st)
+            (remove_empty st))
 
 let cpdfua_args title =
   [       "-create-pdf";