Attributes: Restore boolean attribute & false setter treatment from 3.x

Restore & warn against:
* boolean attributes set to something different than their lowercase names
* boolean attributes queried when set to something different than their
  lowercase names
* non-boolean non-ARIA attributes set to `false`

Fixes gh-504
Ref jquery/jquery#5452
Ref jquery/api.jquery.com#1243

Author: mgol

src/jquery/attributes.js

@@ -1,9 +1,116 @@
 import { migratePatchFunc, migrateWarn } from "../main.js";
+import { jQueryVersionSince } from "../compareVersions.js";
 
 var oldRemoveAttr = jQuery.fn.removeAttr,
+	oldJQueryAttr = jQuery.attr,
 	oldToggleClass = jQuery.fn.toggleClass,
-	rbooleans = /^(?:checked|selected|async|autofocus|autoplay|controls|defer|disabled|hidden|ismap|loop|multiple|open|readonly|required|scoped)$/i,
-	rmatchNonSpace = /\S+/g;
+	booleans = "checked|selected|async|autofocus|autoplay|controls|defer|" +
+		"disabled|hidden|ismap|loop|multiple|open|readonly|required|scoped",
+	rbooleans = new RegExp( "^(?:" + booleans + ")$", "i" ),
+	rmatchNonSpace = /\S+/g,
+
+	// Some formerly boolean attributes gained new values with special meaning.
+	// Skip the old boolean attr logic for those values.
+	extraBoolAttrValues = {
+		hidden: [ "until-found" ]
+	};
+
+// HTML boolean attributes have special behavior:
+// we consider the lowercase name to be the only valid value, so
+// getting (if the attribute is present) normalizes to that, as does
+// setting to any non-`false` value (and setting to `false` removes the attribute).
+// See https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#boolean-attributes
+jQuery.each( booleans.split( "|" ), function( _i, name ) {
+	var origAttrHooks = jQuery.attrHooks[ name ] || {};
+	jQuery.attrHooks[ name ] = {
+		get: origAttrHooks.get || function( elem ) {
+			var attrValue;
+
+			if ( jQuery.migrateIsPatchEnabled( "boolean-attributes" ) ) {
+				attrValue = elem.getAttribute( name );
+
+				if ( attrValue !== name && attrValue != null &&
+					( extraBoolAttrValues[ name ] || [] ).indexOf( attrValue ) === -1
+				) {
+					migrateWarn( "boolean-attributes",
+						"Boolean attribute '" + name +
+							"' value is different from its lowercased name" );
+
+					// jQuery <4 attr hooks setup is complex: there are attr
+					// hooks, bool hooks and selector attr handles. Only
+					// implement the logic in jQuery >=4 where it's missing
+					// and there are only attr hooks.
+					if ( jQueryVersionSince( "4.0.0" ) ) {
+						return name.toLowerCase();
+					}
+					return null;
+				}
+			}
+
+			return null;
+		},
+
+		set: origAttrHooks.set || function( elem, value, name ) {
+			if ( jQuery.migrateIsPatchEnabled( "boolean-attributes" ) ) {
+				if ( value !== name &&
+					( extraBoolAttrValues[ name ] || [] ).indexOf( value ) === -1
+				) {
+					if ( value !== false ) {
+						migrateWarn( "boolean-attributes",
+							"Boolean attribute '" + name +
+								"' is not set to its lowercased name" );
+					}
+
+					if ( value === false ) {
+
+						// Remove boolean attributes when set to false
+						jQuery.removeAttr( elem, name );
+					} else {
+						elem.setAttribute( name, name );
+					}
+					return name;
+				}
+			} else if ( !jQueryVersionSince( "4.0.0" ) ) {
+
+				// jQuery <4 uses a private `boolHook` for the boolean attribute
+				// setter. It's only activated if `attrHook` is not set, but we set
+				// it here in Migrate. Since we cannot access it, let's just repeat
+				// its contents here.
+				if ( value === false ) {
+
+					// Remove boolean attributes when set to false
+					jQuery.removeAttr( elem, name );
+				} else {
+					elem.setAttribute( name, name );
+				}
+				return name;
+			}
+		}
+	};
+} );
+
+migratePatchFunc( jQuery, "attr", function( elem, name, value ) {
+	var nType = elem.nodeType;
+
+	// Fallback to the original method on text, comment and attribute nodes
+	// and when attributes are not supported.
+	if ( nType === 3 || nType === 8 || nType === 2 ||
+			typeof elem.getAttribute === "undefined" ) {
+		return oldJQueryAttr.apply( this, arguments );
+	}
+
+	if ( value === false && name.toLowerCase().indexOf( "aria-" ) !== 0 &&
+			!rbooleans.test( name ) ) {
+		migrateWarn( "attr-false",
+			"Setting the non-ARIA non-boolean attribute '" + name +
+				"' to false" );
+
+		jQuery.attr( elem, name, "false" );
+		return;
+	}
+
+	return oldJQueryAttr.apply( this, arguments );
+}, "attr-false" );
 
 migratePatchFunc( jQuery.fn, "removeAttr", function( name ) {
 	var self = this,