Selectmenu: Properly set width for button

Fixes #10145
Closes jquerygh-1296

Author: scottgonzalez

tests/unit/selectmenu/selectmenu_options.js

@@ -86,8 +86,8 @@ test( "CSS styles", function() {
 });
 
 
-test( "Width", function() {
-	expect( 8 );
+test( "width", function() {
+	expect( 9 );
 
 	var button, menu,
 		element = $( "#speed" );
@@ -124,6 +124,14 @@ test( "Width", function() {
 	equal( button.outerWidth(), element.outerWidth(), "button width with long option" );
 	element.selectmenu( "open" );
 	ok( menu.outerWidth() >= element.outerWidth(), "menu width with long option" );
+
+	element.parent().outerWidth( 300 );
+	element
+		.selectmenu( "destroy" )
+		.css( "width", "100%" )
+		.selectmenu();
+	button = element.selectmenu( "widget" );
+	equal( button.outerWidth(), 300, "button width fills container" );
 });
 
 })( jQuery );

ui/selectmenu.js

@@ -106,7 +106,7 @@ return $.widget( "ui.selectmenu", {
 			.appendTo( this.button );
 
 		this._setText( this.buttonText, this.element.find( "option:selected" ).text() );
-		this._setOption( "width", this.options.width );
+		this._resizeButton();
 
 		this._on( this.button, this._buttonEvents );
 		this.button.one( "focusin", function() {
@@ -186,7 +186,9 @@ return $.widget( "ui.selectmenu", {
 	refresh: function() {
 		this._refreshMenu();
 		this._setText( this.buttonText, this._getSelectedItem().text() );
-		this._setOption( "width", this.options.width );
+		if ( !this.options.width ) {
+			this._resizeButton();
+		}
 	},
 
 	_refreshMenu: function() {
@@ -475,10 +477,7 @@ return $.widget( "ui.selectmenu", {
 		}
 
 		if ( key === "width" ) {
-			if ( !value ) {
-				value = this.element.outerWidth();
-			}
-			this.button.outerWidth( value );
+			this._resizeButton();
 		}
 	},
 
@@ -511,6 +510,17 @@ return $.widget( "ui.selectmenu", {
 		this.menu.attr( "aria-hidden", !this.isOpen );
 	},
 
+	_resizeButton: function() {
+		var width = this.options.width;
+
+		if ( !width ) {
+			width = this.element.show().outerWidth();
+			this.element.hide();
+		}
+
+		this.button.outerWidth( width );
+	},
+
 	_resizeMenu: function() {
 		this.menu.outerWidth( Math.max(
 			this.button.outerWidth(),