Resize find widget on double click

src/vs/editor/contrib/find/findWidget.css

@@ -38,6 +38,7 @@
 	line-height: 19px;
 	transition: top 200ms linear;
 	padding: 0 4px;
+	box-sizing: border-box;
 }
 
 .monaco-editor .find-widget.hiddenEditor {

src/vs/editor/contrib/find/findWidget.ts

@@ -57,7 +57,7 @@ const NLS_MATCHES_COUNT_LIMIT_TITLE = nls.localize('title.matchesCountLimit', "O
 const NLS_MATCHES_LOCATION = nls.localize('label.matchesLocation', "{0} of {1}");
 const NLS_NO_RESULTS = nls.localize('label.noResults', "No Results");
 
-const FIND_WIDGET_INITIAL_WIDTH = 411;
+const FIND_WIDGET_INITIAL_WIDTH = 419;
 const PART_WIDTH = 275;
 const FIND_INPUT_AREA_WIDTH = PART_WIDTH - 54;
 
@@ -1172,6 +1172,39 @@ export class FindWidget extends Widget implements IOverlayWidget, IHorizontalSas
 			this._findInput.inputBox.layout();
 			this._tryUpdateHeight();
 		}));
+
+		this._register(this._resizeSash.onDidReset(() => {
+			// users double click on the sash
+			const currentWidth = dom.getTotalWidth(this._domNode);
+
+			if (currentWidth < FIND_WIDGET_INITIAL_WIDTH) {
+				// The editor is narrow and the width of the find widget is controlled fully by CSS.
+				return;
+			}
+
+			let width = FIND_WIDGET_INITIAL_WIDTH;
+
+			if (!this._resized || currentWidth === FIND_WIDGET_INITIAL_WIDTH) {
+				// 1. never resized before, double click should maximizes it
+				// 2. users resized it already but its width is the same as default
+				width = this._codeEditor.getConfiguration().layoutInfo.width - 28 - this._codeEditor.getConfiguration().layoutInfo.minimapWidth - 15;
+				this._resized = true;
+			} else {
+				/**
+				 * no op, the find widget should be shrinked to its default size.
+				 */
+			}
+
+			const inputBoxWidth = width - FIND_ALL_CONTROLS_WIDTH;
+
+			this._domNode.style.width = `${width}px`;
+			this._findInput.inputBox.width = inputBoxWidth;
+			if (this._isReplaceVisible) {
+				this._replaceInput.width = dom.getTotalWidth(this._findInput.domNode);
+			}
+
+			this._findInput.inputBox.layout();
+		}));
 	}
 
 	private updateAccessibilitySupport(): void {