Adding search support in the reference driver

Signed-off-by: Paul-Elliot <peada@free.fr>

Author: panglesd

doc/driver.md

@@ -217,19 +217,26 @@ let link ?(ignore_output = false) file =
   if not ignore_output then
     add_prefixed_output cmd link_output (Fpath.to_string file) lines
 
-let html_generate ?(ignore_output = false) file source =
+let html_generate ?(ignore_output = false) ?(search_files = []) file source =
   let open Cmd in
   let source = match source with None -> empty | Some source -> v "--source" % p source in
+  let search =
+    List.fold_left
+      (fun acc filename -> acc % "--search-file" % filename)
+      empty
+      (List.map Fpath.filename search_files)
+  in
   let cmd =
-    odoc % "html-generate" %% source % p file % "-o" % "html" % "--theme-uri" % "odoc"
+    odoc % "html-generate" %% source % p file %% search % "-o" % "html" % "--theme-uri" % "odoc"
     % "--support-uri" % "odoc"
   in
   let lines = run cmd in
   if not ignore_output then
     add_prefixed_output cmd generate_output (Fpath.to_string file) lines
 
-let support_files () =
+let support_files  ?(search_files = []) () =
   let open Cmd in
+  let search = List.fold_left (fun acc f -> acc % "--search-file" % p f) empty search_files in
   let cmd = odoc % "support-files" % "-o" % "html/odoc" in
   run cmd
 ```
@@ -582,20 +589,78 @@ let link_all odoc_files =
 
 Now we simply run `odoc html-generate` over all of the resulting `odocl` files.
 This will generate sources, as well as documentation for non-hidden units.
+We notify the generator that the javascript file to use for search is `index.js`.
 
 ```ocaml env=e1
 let generate_all odocl_files =
+  let search_files = [ Fpath.v "index.js" ] in
   let relativize_opt = function None -> None | Some file -> Some (relativize file) in
-  List.iter (fun (f, source) -> ignore(html_generate f (relativize_opt source))) odocl_files;
-  support_files ()
+  List.iter
+    (fun (f, source) -> ignore(html_generate ~search_files f (relativize_opt source)))
+     odocl_files;
+  support_files ~search_files ()
+```
+
+Finally, we generate an index of all values, types, ... This index is meant to be consumed by search engines, to create their own index. It consists of a JSON array, containing entries with the name, full name, associated comment, link and anchor, and kind.
+Generating the index is done via `odoc compile-index`, which create a json file. This second format is meant to be consumed by search engines to populate their search index. Search engines written in OCaml can also call the `Odoc_model.Fold.unit` and  `Odoc_model.Fold.page` function, in conjunction with `Odoc_search.Entry.entry_of_item` in order to get a (version stable) OCaml value of each element to be indexed.
+
+```ocaml env=e1
+let index_generate ?(ignore_output = false) () =
+  let open Cmd in
+  let cmd = odoc % "compile-index" % "-o" % "html/index.json" % "-I" % "." in
+  let lines = run cmd in
+  if not ignore_output then
+    add_prefixed_output cmd generate_output "index compilation" lines;
 ```
 
+We turn the JSON index into a javascript file. In order to never block the UI, this file will be used as a web worker by `odoc`, to perform searches:
+
+- The search query will be sent as a plain string to the web worker, using the standard mechanism of message passing
+- The web worker has to sent back the result as a message to the main thread, containing the list of result. Each entry of this list must have the same form as it had in the original JSON file.
+- The file must be named `index.js` and be located in the `odoc-support` URI.
+
+In this driver, we use the minisearch javascript library. For more involved application, we could use `index.js` to call a server-side search engine via an API call.
+
+```ocaml env=e1
+let js_index () =
+  let index = Bos.OS.File.read Fpath.(v "html" / "index.json") |> get_ok in
+  let minisearch = Bos.OS.File.read Fpath.(v "minisearch.js") |> get_ok in
+  Bos.OS.File.writef Fpath.(v "html" / "odoc" / "index.js") {|%s
+let documents = 
+  %s
+;
+
+let miniSearch = new MiniSearch({
+  fields: ['id', 'doc'], // fields to index for full-text search
+  storeFields: ['display'], // fields to return with search results
+  extractField: (document, fieldName) => {
+    if (fieldName === 'id') {
+      return document.id.map(e => e.kind + "-" + e.name).join('.')
+    }
+    return document[fieldName]
+  }
+})
+
+
+// Index all documents (except Type extensions which don't have a unique ID)
+miniSearch.addAll(documents.filter(entry => entry.extra.kind != "TypeExtension"));
+
+onmessage = (m) => {
+  let query = m.data;
+  let result = miniSearch.search(query);
+  postMessage(result.slice(0,200).map(a => a.display));
+}
+|} minisearch index
+```
+
+
 The following code executes all of the above, and we're done!
 
 ```ocaml env=e1
 let compiled = compile_all () in
 let linked = link_all compiled in
-generate_all linked
+let _ = generate_all linked in
+let () = index_generate () in js_index ()
 ```
 
 Let's see if there was any output from the `odoc` invocations: