feat: Added Editor API to set the ghost text

ace.d.ts

@@ -675,6 +675,8 @@ export namespace Ace {
     showComposition(position: number): void;
     setCompositionText(text: string): void;
     hideComposition(): void;
+    setGhostText(text: string, position: Point): void;
+    removeGhostText(): void;
     setTheme(theme: string, callback?: () => void): void;
     getTheme(): string;
     setStyle(style: string, include?: boolean): void;
@@ -843,6 +845,8 @@ export namespace Ace {
     removeWordLeft(): void;
     removeLineToEnd(): void;
     splitLine(): void;
+    setGhostText(text: string, position: Point): void;
+    removeGhostText(): void;
     transposeLetters(): void;
     toLowerCase(): void;
     toUpperCase(): void;

src/css/editor.css.js

@@ -583,4 +583,9 @@ styles.join("\\n")
     white-space: pre;
     opacity: 0.7;
     margin: 0 10px;
+}
+
+.ace_ghost_text {
+    opacity: 0.5;
+    font-style: italic;
 }`;

src/editor.js

@@ -16,6 +16,7 @@ var CommandManager = require("./commands/command_manager").CommandManager;
 var defaultCommands = require("./commands/default_commands").commands;
 var config = require("./config");
 var TokenIterator = require("./token_iterator").TokenIterator;
+var LineWidgets = require("./line_widgets").LineWidgets;
 
 var clipboard = require("./clipboard");
 
@@ -1425,6 +1426,31 @@ Editor.$uid = 0;
         this.moveCursorToPosition(cursor);
     };
 
+    /**
+     * Set the "ghost" text in provided position. "Ghost" text is a kind of
+     * preview text inside the editor which can be used to preview some code
+     * inline in the editor such as, for example, code completions.
+     * 
+     * @param {String} text Text to be inserted as "ghost" text
+     * @param {object} position Position to insert text to
+     */
+    this.setGhostText = function(text, position) {
+        if (!this.session.widgetManager) {
+            this.session.widgetManager = new LineWidgets(this.session);
+            this.session.widgetManager.attach(this);
+        }
+        this.renderer.setGhostText(text, position);
+    };
+
+    /**
+     * Removes "ghost" text currently displayed in the editor.
+     */
+    this.removeGhostText = function() {
+        if (!this.session.widgetManager) return;
+
+        this.renderer.removeGhostText();
+    };
+
     /**
      * Transposes current line.
      **/

src/line_widgets.js

@@ -182,8 +182,15 @@ function LineWidgets(session) {
             w.el = dom.createElement("div");
             w.el.innerHTML = w.html;
         }
+        if (w.text && !w.el) {
+            w.el = dom.createElement("div");
+            w.el.textContent = w.text;
+        }
         if (w.el) {
             dom.addCssClass(w.el, "ace_lineWidgetContainer");
+            if (w.className) {
+                dom.addCssClass(w.el, w.className);
+            }
             w.el.style.position = "absolute";
             w.el.style.zIndex = 5;
             renderer.container.appendChild(w.el);

src/virtual_renderer.js

@@ -1617,7 +1617,46 @@ var VirtualRenderer = function(container, theme) {
         this.$composition = null;
         this.$cursorLayer.element.style.display = "";
     };
-
+
+    this.setGhostText = function(text, position) {
+        var cursor = this.session.selection.cursor;
+        var insertPosition = position || { row: cursor.row, column: cursor.column };
+
+        this.removeGhostText();
+
+        var textLines = text.split("\n");
+        this.addToken(textLines[0], "ghost_text", insertPosition.row, insertPosition.column);
+        this.$ghostText = {
+            text: text,
+            position: {
+                row: insertPosition.row,
+                column: insertPosition. column
+            }
+        };
+        if (textLines.length > 1) {
+            this.$ghostTextWidget = {
+                text: textLines.slice(1).join("\n"),
+                row: insertPosition.row,
+                column: insertPosition.column,
+                className: "ace_ghost_text"
+            };
+            this.session.widgetManager.addLineWidget(this.$ghostTextWidget);
+        }
+
+    };
+
+    this.removeGhostText = function() {
+        if (!this.$ghostText) return;
+
+        var position = this.$ghostText.position;
+        this.removeExtraToken(position.row, position.column);
+        if (this.$ghostTextWidget) {
+            this.session.widgetManager.removeLineWidget(this.$ghostTextWidget);
+            this.$ghostTextWidget = null;
+        }
+        this.$ghostText = null;
+    };
+
     this.addToken = function(text, type, row, column) {
         var session = this.session;
         session.bgTokenizer.lines[row] = null;

src/virtual_renderer_test.js

@@ -300,6 +300,35 @@ module.exports = {
         ];
         assertCoordsColor(values, imageData.data);
     },
+    "test ghost text": function() {
+        editor.session.setValue("abcdef");
+        editor.setGhostText("Ghost");
+
+        editor.renderer.$loop._flush();
+        assert.equal(editor.renderer.content.textContent, "Ghostabcdef");
+
+        editor.setGhostText("Ghost", {row: 0, column: 3});
+
+        editor.renderer.$loop._flush();
+        assert.equal(editor.renderer.content.textContent, "abcGhostdef");
+
+        editor.setGhostText("Ghost", {row: 0, column: 6});
+
+        editor.renderer.$loop._flush();
+        assert.equal(editor.renderer.content.textContent, "abcdefGhost");
+    },
+
+    "test multiline ghost text": function() {
+        editor.session.setValue("abcdef");
+        editor.renderer.$loop._flush();
+
+        editor.setGhostText("Ghost1\nGhost2\nGhost3", {row: 0, column: 6});
+
+        editor.renderer.$loop._flush();
+        assert.equal(editor.renderer.content.textContent, "abcdefGhost1");
+
+        assert.equal(editor.session.lineWidgets[0].el.textContent, "Ghost2\nGhost3");
+    },
     "test: brackets highlighting": function (done) {
         var renderer = editor.renderer;
         editor.session.setValue(