Rework word completion: Do not reparse whole document unnecessarily

plugins/word-completion/engine.vala

@@ -22,7 +22,7 @@ public class Euclide.Completion.Parser : GLib.Object {
     public const int MINIMUM_WORD_LENGTH = 1;
     public const int MAX_TOKENS = 1000000;
 
-    private Scratch.Plugins.PrefixTree prefix_tree;
+    private Scratch.Plugins.PrefixTree? prefix_tree = null;
 
     public const string DELIMITERS = " .,;:?{}[]()0123456789+=&|<>*\\/\r\n\t\'\"`";
     public static bool is_delimiter (unichar c) {
@@ -53,26 +53,38 @@ public class Euclide.Completion.Parser : GLib.Object {
 
     public void rebuild_word_list (Gtk.TextView view) {
         prefix_tree.clear ();
-        parse_text_view (view);
+        if (view.buffer.text.length > 0) {
+            parse_string (view.buffer.text);
+            text_view_words.@set (view, prefix_tree);
+        }
     }
 
-    public void parse_text_view (Gtk.TextView view) {
-        /* If this view has already been parsed, restore the word list */
+    public bool select_current_tree (Gtk.TextView view) {
+        bool pre_existing = true;
+        if (!text_view_words.has_key (view)) {
+            var new_treemap = new Scratch.Plugins.PrefixTree ();
+            text_view_words.@set (view, new_treemap);
+            pre_existing = false;
+        }
+
         lock (prefix_tree) {
-            if (text_view_words.has_key (view)) {
-                prefix_tree = text_view_words.@get (view);
-            } else {
-                /* Else create a new word list and parse the buffer text */
-                prefix_tree = new Scratch.Plugins.PrefixTree ();
-            }
+            prefix_tree = text_view_words.@get (view);
+            parsing_cancelled = false;
         }
 
-        if (view.buffer.text.length > 0) {
-            parse_string (view.buffer.text);
-            text_view_words.@set (view, prefix_tree);
+        return pre_existing && get_initial_parsing_completed ();
+    }
+
+    public void set_initial_parsing_completed (bool completed) requires (prefix_tree != null) {
+        lock (prefix_tree) {
+            prefix_tree.completed = completed;
         }
     }
 
+    public bool get_initial_parsing_completed () requires (prefix_tree != null) {
+        return prefix_tree.completed;
+    }
+
     public void add_word (string word) {
         if (word.length < MINIMUM_WORD_LENGTH)
             return;

plugins/word-completion/plugin.vala

@@ -19,6 +19,8 @@
  */
 
 public class Scratch.Plugins.Completion : Peas.ExtensionBase, Peas.Activatable {
+    public const int INITIAL_PARSE_DELAY_MSEC = 1000;
+
     public Object object { owned get; construct; }
 
     private List<Gtk.SourceView> text_view_list = new List<Gtk.SourceView> ();
@@ -96,28 +98,33 @@ public class Scratch.Plugins.Completion : Peas.ExtensionBase, Peas.Activatable {
             current_view.completion.add_provider (comp_provider);
             current_view.completion.show_headers = true;
             current_view.completion.show_icons = true;
-            /* Wait a bit to allow text to load then run parser*/
-            timeout_id = Timeout.add (1000, on_timeout_update);
 
         } catch (Error e) {
             warning (e.message);
         }
-    }
 
-    private bool on_timeout_update () {
-        try {
-            new Thread<void*>.try ("word-completion-thread", () => {
-                if (current_view != null)
-                    parser.parse_text_view (current_view as Gtk.TextView);
+        // Check whether there is already a parsed tree
+        if (!parser.select_current_tree (current_view)) {
+            // If not, start initial parsing  after timeout to ensure text loaded
+            var view_to_parse = current_view;
+            timeout_id = Timeout.add (INITIAL_PARSE_DELAY_MSEC, () => {
+                timeout_id = 0;
+                // Check view has not been switched
+                if (view_to_parse == current_view) {
+                    try {
+                        new Thread<void*>.try ("word-completion-thread", () => {
+                            // The initial parse gets cancelled if view switched before complete
+                            parser.rebuild_word_list (view_to_parse);
+                            return null;
+                        });
+                    } catch (Error e) {
+                        warning (e.message);
+                    }
+                }
 
-                return null;
+                return Source.REMOVE;
             });
-        } catch (Error e) {
-            warning (e.message);
         }
-
-        timeout_id = 0;
-        return false;
     }
 
     private bool on_key_press (Gtk.Widget view, Gdk.EventKey event) {

plugins/word-completion/prefix-tree.vala

@@ -11,6 +11,7 @@ namespace Scratch.Plugins {
 
     public class PrefixTree : Object {
         private PrefixNode root;
+        public bool completed { get; set; default = false; }
 
         construct {
             clear ();