Core:Manipulation: Add basic TrustedHTML support

This ensures HTML wrapped in TrustedHTML can be used as an input to jQuery
manipulation methods in a way that doesn't violate the
`require-trusted-types-for` Content Security Policy directive.
This commit builds on previous work needed for trusted types support, including
gh-4642 and gh-4724.

One restriction is that while any TrustedHTML wrapper should work as input
for jQuery methods like `.html()` or `.append()`, for passing directly to the
`jQuery` factory the string must start with `<` and end with `>`; no trailing
or leading whitespaces are allowed. This is necessary as we cannot parse out
a part of the input for further construction; that would violate the CSP rule -
and that's what's done to HTML input not matching these constraints.

No trusted types API is used explicitly in source; the majority of the work is
ensuring we don't pass the input converted to string to APIs that would
eventually assign it to `innerHTML`. This extra cautiousness is caused by the
API being Blink-only, at least for now.

The ban on passing strings to `innerHTML` means support tests relying on such
assignments are impossible. We don't currently have such tests on the `main`
branch but we used to have many of them in the 3.x & older lines. If there's
a need to re-add such a test, we'll need an escape hatch to skip them for apps
needing CSP-enforced TrustedHTML.

See https://web.dev/trusted-types/ for more information about TrustedHTML.

Fixes gh-4409
Closes gh-4927
Ref gh-4642
Ref gh-4724

12 files changed, 170 insertions, 46 deletions

diff --git a/src/core.js b/src/core.js
index 31d749dd1..4f5731ae1 100644
--- a/src/core.js
+++ b/src/core.js
@@ -10,9 +10,8 @@ import hasOwn from "./var/hasOwn.js";
 import fnToString from "./var/fnToString.js";
 import ObjectFunctionString from "./var/ObjectFunctionString.js";
 import support from "./var/support.js";
-import isWindow from "./var/isWindow.js";
+import isArrayLike from "./core/isArrayLike.js";
 import DOMEval from "./core/DOMEval.js";
-import toType from "./core/toType.js";
 
 var version = "@VERSION",
 
@@ -398,17 +397,4 @@ jQuery.each( "Boolean Number String Function Array Date RegExp Object Error Symb
 		class2type[ "[object " + name + "]" ] = name.toLowerCase();
 	} );
 
-function isArrayLike( obj ) {
-
-	var length = !!obj && obj.length,
-		type = toType( obj );
-
-	if ( typeof obj === "function" || isWindow( obj ) ) {
-		return false;
-	}
-
-	return type === "array" || length === 0 ||
-		typeof length === "number" && length > 0 && ( length - 1 ) in obj;
-}
-
 export default jQuery;
diff --git a/src/core/init.js b/src/core/init.js
index a97fc1060..8fc24d8dd 100644
--- a/src/core/init.js
+++ b/src/core/init.js
@@ -2,6 +2,7 @@
 import jQuery from "../core.js";
 import document from "../var/document.js";
 import rsingleTag from "./var/rsingleTag.js";
+import isObviousHtml from "./isObviousHtml.js";
 
 import "../traversing/findFilter.js";
 
@@ -26,20 +27,41 @@ var rootjQuery,
 		// so migrate can support jQuery.sub (gh-2101)
 		root = root || rootjQuery;
 
-		// Handle HTML strings
-		if ( typeof selector === "string" ) {
-			if ( selector[ 0 ] === "<" &&
-				selector[ selector.length - 1 ] === ">" &&
-				selector.length >= 3 ) {
+		// HANDLE: $(DOMElement)
+		if ( selector.nodeType ) {
+			this[ 0 ] = selector;
+			this.length = 1;
+			return this;
+
+		// HANDLE: $(function)
+		// Shortcut for document ready
+		} else if ( typeof selector === "function" ) {
+			return root.ready !== undefined ?
+				root.ready( selector ) :
+
+				// Execute immediately if ready is not present
+				selector( jQuery );
+
+		} else {
 
-				// Assume that strings that start and end with <> are HTML and skip the regex check
+			// Handle obvious HTML strings
+			match = selector + "";
+			if ( isObviousHtml( match ) ) {
+
+				// Assume that strings that start and end with <> are HTML and skip
+				// the regex check. This also handles browser-supported HTML wrappers
+				// like TrustedHTML.
 				match = [ null, selector, null ];
 
-			} else {
+			// Handle HTML strings or selectors
+			} else if ( typeof selector === "string" ) {
 				match = rquickExpr.exec( selector );
+			} else {
+				return jQuery.makeArray( selector, this );
 			}
 
 			// Match html or make sure no context is specified for #id
+			// Note: match[1] may be a string or a TrustedHTML wrapper
 			if ( match && ( match[ 1 ] || !context ) ) {
 
 				// HANDLE: $(html) -> $(array)
@@ -84,7 +106,7 @@ var rootjQuery,
 					return this;
 				}
 
-			// HANDLE: $(expr, $(...))
+			// HANDLE: $(expr) & $(expr, $(...))
 			} else if ( !context || context.jquery ) {
 				return ( context || root ).find( selector );
 
@@ -93,24 +115,8 @@ var rootjQuery,
 			} else {
 				return this.constructor( context ).find( selector );
 			}
-
-		// HANDLE: $(DOMElement)
-		} else if ( selector.nodeType ) {
-			this[ 0 ] = selector;
-			this.length = 1;
-			return this;
-
-		// HANDLE: $(function)
-		// Shortcut for document ready
-		} else if ( typeof selector === "function" ) {
-			return root.ready !== undefined ?
-				root.ready( selector ) :
-
-				// Execute immediately if ready is not present
-				selector( jQuery );
 		}
 
-		return jQuery.makeArray( selector, this );
 	};
 
 // Give the init function the jQuery prototype for later instantiation
diff --git a/src/core/isArrayLike.js b/src/core/isArrayLike.js
new file mode 100644
index 000000000..988c483d3
--- /dev/null
+++ b/src/core/isArrayLike.js
@@ -0,0 +1,17 @@
+import toType from "./toType.js";
+import isWindow from "../var/isWindow.js";
+
+function isArrayLike( obj ) {
+
+	var length = !!obj && obj.length,
+		type = toType( obj );
+
+	if ( typeof obj === "function" || isWindow( obj ) ) {
+		return false;
+	}
+
+	return type === "array" || length === 0 ||
+		typeof length === "number" && length > 0 && ( length - 1 ) in obj;
+}
+
+export default isArrayLike;
diff --git a/src/core/isObviousHtml.js b/src/core/isObviousHtml.js
new file mode 100644
index 000000000..976f81219
--- /dev/null
+++ b/src/core/isObviousHtml.js
@@ -0,0 +1,7 @@
+function isObviousHtml( input ) {
+	return input[ 0 ] === "<" &&
+		input[ input.length - 1 ] === ">" &&
+		input.length >= 3;
+}
+
+export default isObviousHtml;
diff --git a/src/core/parseHTML.js b/src/core/parseHTML.js
index 15278fa02..b522a5f7b 100644
--- a/src/core/parseHTML.js
+++ b/src/core/parseHTML.js
@@ -2,13 +2,14 @@ import jQuery from "../core.js";
 import document from "../var/document.js";
 import rsingleTag from "./var/rsingleTag.js";
 import buildFragment from "../manipulation/buildFragment.js";
+import isObviousHtml from "./isObviousHtml.js";
 
-// Argument "data" should be string of html
+// Argument "data" should be string of html or a TrustedHTML wrapper of obvious HTML
 // context (optional): If specified, the fragment will be created in this context,
 // defaults to document
 // keepScripts (optional): If true, will include scripts passed in the html string
 jQuery.parseHTML = function( data, context, keepScripts ) {
-	if ( typeof data !== "string" ) {
+	if ( typeof data !== "string" && !isObviousHtml( data + "" ) ) {
 		return [];
 	}
 	if ( typeof context === "boolean" ) {
diff --git a/src/manipulation/buildFragment.js b/src/manipulation/buildFragment.js
index 9ac71acc9..d6f8e5783 100644
--- a/src/manipulation/buildFragment.js
+++ b/src/manipulation/buildFragment.js
@@ -7,6 +7,7 @@ import rscriptType from "./var/rscriptType.js";
 import wrapMap from "./wrapMap.js";
 import getAll from "./getAll.js";
 import setGlobalEval from "./setGlobalEval.js";
+import isArrayLike from "../core/isArrayLike.js";
 
 var rhtml = /<|&#?\w+;/;
 
@@ -23,7 +24,7 @@ function buildFragment( elems, context, scripts, selection, ignored ) {
 		if ( elem || elem === 0 ) {
 
 			// Add nodes directly
-			if ( toType( elem ) === "object" ) {
+			if ( toType( elem ) === "object" && ( elem.nodeType || isArrayLike( elem ) ) ) {
 				jQuery.merge( nodes, elem.nodeType ? [ elem ] : elem );
 
 			// Convert non-html into a text node
diff --git a/test/.eslintrc.json b/test/.eslintrc.json
index f52842efa..a5509180d 100644
--- a/test/.eslintrc.json
+++ b/test/.eslintrc.json
@@ -14,6 +14,7 @@
 		"require": false,
 		"Promise": false,
 		"Symbol": false,
+		"trustedTypes": false,
 		"QUnit": false,
 		"ajaxTest": false,
 		"testIframe": false,
diff --git a/test/data/csp.include.html b/test/data/csp.include.html
index 17e2ef0d8..59b87f212 100644
--- a/test/data/csp.include.html
+++ b/test/data/csp.include.html
@@ -3,7 +3,7 @@
 <head>
 	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 	<title>CSP Test Page</title>
-	<script src="../jquery.js"></script>
+	<script src="../../dist/jquery.min.js"></script>
 	<script src="iframeTest.js"></script>
 	<script src="support/csp.js"></script>
 	<script src="support/getComputedSupport.js"></script>
diff --git a/test/data/mock.php b/test/data/mock.php
index d0ed6f2c1..268ad06ef 100644
--- a/test/data/mock.php
+++ b/test/data/mock.php
@@ -215,7 +215,7 @@ QUnit.assert.ok( true, "mock executed");';
 	}
 
 	protected function cspFrame( $req ) {
-		header( "Content-Security-Policy: default-src 'self'; report-uri ./mock.php?action=cspLog" );
+		header( "Content-Security-Policy: default-src 'self'; require-trusted-types-for 'script'; report-uri ./mock.php?action=cspLog" );
 		header( 'Content-type: text/html' );
 		echo file_get_contents( __DIR__ . '/csp.include.html' );
 	}
@@ -228,7 +228,7 @@ QUnit.assert.ok( true, "mock executed");';
 	}
 
 	protected function cspAjaxScript( $req ) {
-		header( "Content-Security-Policy: script-src 'self'; report-uri /base/test/data/mock.php?action=cspLog" );
+		header( "Content-Security-Policy: script-src 'self'; report-uri ./mock.php?action=cspLog" );
 		header( 'Content-type: text/html' );
 		echo file_get_contents( __DIR__ . '/csp-ajax-script.html' );
 	}
@@ -241,6 +241,12 @@ QUnit.assert.ok( true, "mock executed");';
 		file_put_contents( $this->cspFile, '' );
 	}
 
+	protected function trustedHtml( $req ) {
+		header( "Content-Security-Policy: require-trusted-types-for 'script'; report-uri ./mock.php?action=cspLog" );
+		header( 'Content-type: text/html' );
+		echo file_get_contents( __DIR__ . '/trusted-html.html' );
+	}
+
 	protected function errorWithScript( $req ) {
 		header( 'HTTP/1.0 404 Not Found' );
 		if ( isset( $req->query['withScriptContentType'] ) ) {
diff --git a/test/data/trusted-html.html b/test/data/trusted-html.html
new file mode 100644
index 000000000..063779a62
--- /dev/null
+++ b/test/data/trusted-html.html
@@ -0,0 +1,75 @@
+<!DOCTYPE html>
+<html>
+<head>
+	<meta charset=utf-8 />
+	<title>body</title>
+</head>
+<body>
+<div id="qunit-fixture"></div>
+<script src="../../dist/jquery.min.js"></script>
+<script src="iframeTest.js"></script>
+<script>
+	var i, input, elem, tags, policy,
+		results = [],
+		inputs = [
+			[ "<div></div>", "<div class='test'></div>", [ "div" ] ],
+			[ "<div></div>", "<div class='test'></div><span class='test'></span>",
+				[ "div", "span" ] ],
+			[ "<table></table>", "<td class='test'></td>", [ "td" ] ],
+			[ "<select></select>", "<option class='test'></option>", [ "option" ] ]
+		];
+
+	function runTests( messagePrefix, getHtmlWrapper ) {
+		for ( i = 0; i < inputs.length; i++ ) {
+			input = inputs[ i ];
+			elem = jQuery( getHtmlWrapper( input[ 0 ] ) );
+			elem.append( getHtmlWrapper( input[ 1 ] ) );
+			tags = elem.find( ".test" ).toArray().map( function( node ) {
+				return node.nodeName.toLowerCase();
+			} );
+			results.push( {
+				actual: tags,
+				expected: input[ 2 ],
+				message: messagePrefix + ": " + input[ 2 ].join( ", " )
+			} );
+		}
+
+		elem = jQuery( getHtmlWrapper( "<div></div>" ) );
+		elem.append( getHtmlWrapper( "text content" ) );
+		results.push( {
+			actual: elem.html(),
+			expected: "text content",
+			message: messagePrefix + ": text content properly appended"
+		} );
+	}
+
+	if ( typeof trustedTypes !== "undefined" ) {
+		policy = trustedTypes.createPolicy( "jquery-test-policy", {
+			createHTML: function( html ) {
+				return html;
+			}
+		} );
+
+		runTests( "TrustedHTML", function wrapInTrustedHtml( input ) {
+			return policy.createHTML( input );
+		} );
+	} else {
+
+		// No TrustedHTML support so let's at least run tests with object wrappers
+		// with a proper `toString` function. This also shows that jQuery support
+		// of TrustedHTML is generic and would work with similar APIs out of the box
+		// as well. Ideally, we'd run these tests in browsers with TrustedHTML support
+		// as well but due to the CSP TrustedHTML enforcement these tests would fail.
+		runTests( "Object wrapper", function( input ) {
+			return {
+				toString: function toString() {
+					return input;
+				}
+			};
+		} );
+	}
+
+	startIframeTest( results );
+</script>
+</body>
+</html>
diff --git a/test/middleware-mockserver.js b/test/middleware-mockserver.js
index 04b01d652..0bd44f95b 100644
--- a/test/middleware-mockserver.js
+++ b/test/middleware-mockserver.js
@@ -222,7 +222,7 @@ var mocks = {
 	cspFrame: function( req, resp ) {
 		resp.writeHead( 200, {
 			"Content-Type": "text/html",
-			"Content-Security-Policy": "default-src 'self'; report-uri /base/test/data/mock.php?action=cspLog"
+			"Content-Security-Policy": "default-src 'self'; require-trusted-types-for 'script'; report-uri /base/test/data/mock.php?action=cspLog"
 		} );
 		var body = fs.readFileSync( __dirname + "/data/csp.include.html" ).toString();
 		resp.end( body );
@@ -256,6 +256,14 @@ var mocks = {
 		resp.writeHead( 200 );
 		resp.end();
 	},
+	trustedHtml: function( req, resp ) {
+		resp.writeHead( 200, {
+			"Content-Type": "text/html",
+			"Content-Security-Policy": "require-trusted-types-for 'script'; report-uri /base/test/data/mock.php?action=cspLog"
+		} );
+		var body = fs.readFileSync( __dirname + "/data/trusted-html.html" ).toString();
+		resp.end( body );
+	},
 	errorWithScript: function( req, resp ) {
 		if ( req.query.withScriptContentType ) {
 			resp.writeHead( 404, { "Content-Type": "application/javascript" } );
diff --git a/test/unit/manipulation.js b/test/unit/manipulation.js
index 8262516a9..30bf169ac 100644
--- a/test/unit/manipulation.js
+++ b/test/unit/manipulation.js
@@ -3008,3 +3008,19 @@ QUnit.test( "Works with invalid attempts to close the table wrapper", function(
 	assert.strictEqual( elem[ 0 ].nodeName.toLowerCase(), "td", "First element is td" );
 	assert.strictEqual( elem[ 1 ].nodeName.toLowerCase(), "td", "Second element is td" );
 } );
+
+// Test trustedTypes support in browsers where they're supported (currently Chrome 83+).
+// Browsers with no TrustedHTML support still run tests on object wrappers with
+// a proper `toString` function.
+testIframe(
+	"Basic TrustedHTML support (gh-4409)",
+	"mock.php?action=trustedHtml",
+	function( assert, jQuery, window, document, test ) {
+
+		assert.expect( 5 );
+
+		test.forEach( function( result ) {
+			assert.deepEqual( result.actual, result.expected, result.message );
+		} );
+	}
+);