LibWeb: Adjust create_document_for_inline_content() for future use

(Apologies for bad commit title, it's hard to explain in such a short
space!)

We're going to need to call this for producing markdown and gemini
documents, both of which need a Document and Realm to fetch the entire
response body, so that they can then generate their HTML. So this
commit modifies `create_document_for_inline_content()` to take a lambda
instead of a fixed HTML string, to support these uses.

Also, we always return a nonnull pointer, so make that the return type.

This is a move and change in the same commit, (Sorry!) but all the
changes are to the function signature and step 6.

Userland/Libraries/LibWeb/DOM/DocumentLoading.cpp

@@ -545,71 +545,4 @@ JS::GCPtr<DOM::Document> load_document(HTML::NavigationParams navigation_params)
     return nullptr;
 }
 
-// https://html.spec.whatwg.org/multipage/document-lifecycle.html#read-ua-inline
-JS::GCPtr<DOM::Document> create_document_for_inline_content(JS::GCPtr<HTML::Navigable> navigable, Optional<String> navigation_id, StringView content_html)
-{
-    auto& vm = navigable->vm();
-
-    // 1. Let origin be a new opaque origin.
-    HTML::Origin origin {};
-
-    // 2. Let coop be a new cross-origin opener policy.
-    auto coop = HTML::CrossOriginOpenerPolicy {};
-
-    // 3. Let coopEnforcementResult be a new cross-origin opener policy enforcement result with
-    //    url: response's URL
-    //    origin: origin
-    //    cross-origin opener policy: coop
-    HTML::CrossOriginOpenerPolicyEnforcementResult coop_enforcement_result {
-        .url = AK::URL("about:error"), // AD-HOC
-        .origin = origin,
-        .cross_origin_opener_policy = coop
-    };
-
-    // 4. Let navigationParams be a new navigation params with
-    //    id: navigationId
-    //    navigable: navigable
-    //    request: null
-    //    response: a new response
-    //    origin: origin
-    //    fetch controller: null
-    //    commit early hints: null
-    //    COOP enforcement result: coopEnforcementResult
-    //    reserved environment: null
-    //    policy container: a new policy container
-    //    final sandboxing flag set: an empty set
-    //    cross-origin opener policy: coop
-    //    FIXME: navigation timing type: navTimingType
-    //    about base URL: null
-    auto response = Fetch::Infrastructure::Response::create(vm);
-    response->url_list().append(AK::URL("about:error")); // AD-HOC: https://github.com/whatwg/html/issues/9122
-    HTML::NavigationParams navigation_params {
-        .id = navigation_id,
-        .navigable = navigable,
-        .request = {},
-        .response = *response,
-        .fetch_controller = nullptr,
-        .commit_early_hints = nullptr,
-        .coop_enforcement_result = move(coop_enforcement_result),
-        .reserved_environment = {},
-        .origin = move(origin),
-        .policy_container = HTML::PolicyContainer {},
-        .final_sandboxing_flag_set = HTML::SandboxingFlagSet {},
-        .cross_origin_opener_policy = move(coop),
-        .about_base_url = {},
-    };
-
-    // 5. Let document be the result of creating and initializing a Document object given "html", "text/html", and navigationParams.
-    auto document = DOM::Document::create_and_initialize(DOM::Document::Type::HTML, "text/html"_string, navigation_params).release_value_but_fixme_should_propagate_errors();
-
-    // 6. Either associate document with a custom rendering that is not rendered using the normal Document rendering rules, or mutate document until it represents the content the
-    //    user agent wants to render.
-    auto parser = HTML::HTMLParser::create(document, content_html, "utf-8");
-    document->set_url(AK::URL("about:error"));
-    parser->run();
-
-    // 7. Return document.
-    return document;
-}
-
 }

Userland/Libraries/LibWeb/DOM/DocumentLoading.h

@@ -14,6 +14,71 @@ namespace Web {
 bool build_xml_document(DOM::Document& document, ByteBuffer const& data, Optional<String> content_encoding);
 bool parse_document(DOM::Document& document, ByteBuffer const& data, Optional<String> content_encoding);
 JS::GCPtr<DOM::Document> load_document(HTML::NavigationParams navigation_params);
-JS::GCPtr<DOM::Document> create_document_for_inline_content(JS::GCPtr<HTML::Navigable> navigable, Optional<String> navigation_id, StringView content_html);
+
+// https://html.spec.whatwg.org/multipage/document-lifecycle.html#read-ua-inline
+template<typename MutateDocument>
+JS::NonnullGCPtr<DOM::Document> create_document_for_inline_content(JS::GCPtr<HTML::Navigable> navigable, Optional<String> navigation_id, MutateDocument mutate_document)
+{
+    auto& vm = navigable->vm();
+
+    // 1. Let origin be a new opaque origin.
+    HTML::Origin origin {};
+
+    // 2. Let coop be a new cross-origin opener policy.
+    auto coop = HTML::CrossOriginOpenerPolicy {};
+
+    // 3. Let coopEnforcementResult be a new cross-origin opener policy enforcement result with
+    //    url: response's URL
+    //    origin: origin
+    //    cross-origin opener policy: coop
+    HTML::CrossOriginOpenerPolicyEnforcementResult coop_enforcement_result {
+        .url = AK::URL("about:error"), // AD-HOC
+        .origin = origin,
+        .cross_origin_opener_policy = coop
+    };
+
+    // 4. Let navigationParams be a new navigation params with
+    //    id: navigationId
+    //    navigable: navigable
+    //    request: null
+    //    response: a new response
+    //    origin: origin
+    //    fetch controller: null
+    //    commit early hints: null
+    //    COOP enforcement result: coopEnforcementResult
+    //    reserved environment: null
+    //    policy container: a new policy container
+    //    final sandboxing flag set: an empty set
+    //    cross-origin opener policy: coop
+    //    FIXME: navigation timing type: navTimingType
+    //    about base URL: null
+    auto response = Fetch::Infrastructure::Response::create(vm);
+    response->url_list().append(AK::URL("about:error")); // AD-HOC: https://github.com/whatwg/html/issues/9122
+    HTML::NavigationParams navigation_params {
+        .id = navigation_id,
+        .navigable = navigable,
+        .request = {},
+        .response = *response,
+        .fetch_controller = nullptr,
+        .commit_early_hints = nullptr,
+        .coop_enforcement_result = move(coop_enforcement_result),
+        .reserved_environment = {},
+        .origin = move(origin),
+        .policy_container = HTML::PolicyContainer {},
+        .final_sandboxing_flag_set = HTML::SandboxingFlagSet {},
+        .cross_origin_opener_policy = move(coop),
+        .about_base_url = {},
+    };
+
+    // 5. Let document be the result of creating and initializing a Document object given "html", "text/html", and navigationParams.
+    auto document = DOM::Document::create_and_initialize(DOM::Document::Type::HTML, "text/html"_string, navigation_params).release_value_but_fixme_should_propagate_errors();
+
+    // 6. Either associate document with a custom rendering that is not rendered using the normal Document rendering rules, or mutate document until it represents the content the
+    //    user agent wants to render.
+    mutate_document(*document);
+
+    // 7. Return document.
+    return document;
+}
 
 }

Userland/Libraries/LibWeb/HTML/Navigable.cpp

@@ -20,6 +20,7 @@
 #include <LibWeb/HTML/Navigation.h>
 #include <LibWeb/HTML/NavigationParams.h>
 #include <LibWeb/HTML/POSTResource.h>
+#include <LibWeb/HTML/Parser/HTMLParser.h>
 #include <LibWeb/HTML/SandboxingFlagSet.h>
 #include <LibWeb/HTML/Scripting/ClassicScript.h>
 #include <LibWeb/HTML/SessionHistoryEntry.h>
@@ -1106,7 +1107,11 @@ WebIDL::ExceptionOr<void> Navigable::populate_session_history_entry_document(
             //    The inline content should indicate to the user the sort of error that occurred.
             // FIXME: Add error message to generated error page
             auto error_html = load_error_page(entry->url).release_value_but_fixme_should_propagate_errors();
-            entry->document_state->set_document(create_document_for_inline_content(this, navigation_id, error_html));
+            entry->document_state->set_document(create_document_for_inline_content(this, navigation_id, [error_html](auto& document) {
+                auto parser = HTML::HTMLParser::create(document, error_html, "utf-8");
+                document.set_url(AK::URL("about:error"));
+                parser->run();
+            }));
 
             // 2. Set entry's document state's document's salvageable to false.
             entry->document_state->document()->set_salvageable(false);