LibJS+WebContent+js: Bring console.trace() to spec

The spec very kindly defines `Printer` as accepting
"Implementation-specific representations of printable things such as a
stack trace or group." for the `args`. We make use of that here by
passing the `Trace` itself to `Printer`, instead of having to produce a
representation of the stack trace in advance and then pass that to
`Printer`. That both avoids the hassle of tracking whether the data has
been html-encoded or not, and means clients don't have to implement the
whole `trace()` algorithm, but only the code needed to output the trace.

Userland/Libraries/LibJS/Console.cpp

@@ -87,11 +87,36 @@ Value Console::clear()
     return js_undefined();
 }
 
-Value Console::trace()
+// 1.1.8. trace(...data), https://console.spec.whatwg.org/#trace
+ThrowCompletionOr<Value> Console::trace()
 {
-    if (m_client)
-        return m_client->trace();
-    return js_undefined();
+    if (!m_client)
+        return js_undefined();
+
+    // 1. Let trace be some implementation-specific, potentially-interactive representation of the callstack from where this function was called.
+    Console::Trace trace;
+    auto& execution_context_stack = vm().execution_context_stack();
+    // NOTE: -2 to skip the console.trace() execution context
+    for (ssize_t i = execution_context_stack.size() - 2; i >= 0; --i) {
+        auto& function_name = execution_context_stack[i]->function_name;
+        trace.stack.append(function_name.is_empty() ? "<anonymous>" : function_name);
+    }
+
+    // 2. Optionally, let formattedData be the result of Formatter(data), and incorporate formattedData as a label for trace.
+    if (vm().argument_count() > 0) {
+        StringBuilder builder;
+        auto data = vm_arguments();
+        auto formatted_data = TRY(m_client->formatter(data));
+        for (auto const& item : formatted_data) {
+            if (!builder.is_empty())
+                builder.append(' ');
+            builder.append(TRY(item.to_string(global_object())));
+        }
+        trace.label = builder.to_string();
+    }
+
+    // 3. Perform Printer("trace", « trace »).
+    return m_client->printer(JS::Console::LogLevel::Trace, trace);
 }
 
 // 1.2.1. count(label), https://console.spec.whatwg.org/#count
@@ -237,16 +262,6 @@ VM& ConsoleClient::vm()
     return global_object().vm();
 }
 
-Vector<String> ConsoleClient::get_trace() const
-{
-    Vector<String> trace;
-    auto& execution_context_stack = m_console.global_object().vm().execution_context_stack();
-    // NOTE: -2 to skip the console.trace() execution context
-    for (ssize_t i = execution_context_stack.size() - 2; i >= 0; --i)
-        trace.append(execution_context_stack[i]->function_name);
-    return trace;
-}
-
 // 2.1. Logger(logLevel, args), https://console.spec.whatwg.org/#logger
 ThrowCompletionOr<Value> ConsoleClient::logger(Console::LogLevel log_level, Vector<Value>& args)
 {

Userland/Libraries/LibJS/Console.h

@@ -43,6 +43,11 @@ public:
         Warn,
     };
 
+    struct Trace {
+        String label;
+        Vector<String> stack;
+    };
+
     explicit Console(GlobalObject&);
 
     void set_client(ConsoleClient& client) { m_client = &client; }
@@ -62,7 +67,7 @@ public:
     ThrowCompletionOr<Value> log();
     ThrowCompletionOr<Value> warn();
     Value clear();
-    Value trace();
+    ThrowCompletionOr<Value> trace();
     ThrowCompletionOr<Value> count();
     ThrowCompletionOr<Value> count_reset();
     ThrowCompletionOr<Value> assert_();
@@ -85,10 +90,9 @@ public:
 
     ThrowCompletionOr<Value> logger(Console::LogLevel log_level, Vector<Value>& args);
     ThrowCompletionOr<Vector<Value>> formatter(Vector<Value>& args);
-    virtual ThrowCompletionOr<Value> printer(Console::LogLevel log_level, Vector<Value>&) = 0;
+    virtual ThrowCompletionOr<Value> printer(Console::LogLevel log_level, Variant<Vector<Value>, Console::Trace>) = 0;
 
     virtual void clear() = 0;
-    virtual Value trace() = 0;
 
 protected:
     virtual ~ConsoleClient() = default;
@@ -98,8 +102,6 @@ protected:
     GlobalObject& global_object() { return m_console.global_object(); }
     const GlobalObject& global_object() const { return m_console.global_object(); }
 
-    Vector<String> get_trace() const;
-
     Console& m_console;
 };
 

Userland/Services/WebContent/WebContentConsoleClient.cpp

@@ -120,24 +120,25 @@ void WebContentConsoleClient::clear()
     clear_output();
 }
 
-JS::Value WebContentConsoleClient::trace()
-{
-    StringBuilder html;
-    html.append(escape_html_entities(vm().join_arguments()));
-    auto trace = get_trace();
-    for (auto& function_name : trace) {
-        if (function_name.is_empty())
-            function_name = "<anonymous>";
-        html.appendff(" -> {}<br>", function_name);
-    }
-    print_html(html.string_view());
-    return JS::js_undefined();
-}
-
 // 2.3. Printer(logLevel, args[, options]), https://console.spec.whatwg.org/#printer
-JS::ThrowCompletionOr<JS::Value> WebContentConsoleClient::printer(JS::Console::LogLevel log_level, Vector<JS::Value>& arguments)
+JS::ThrowCompletionOr<JS::Value> WebContentConsoleClient::printer(JS::Console::LogLevel log_level, Variant<Vector<JS::Value>, JS::Console::Trace> arguments)
 {
-    auto output = String::join(" ", arguments);
+    if (log_level == JS::Console::LogLevel::Trace) {
+        auto trace = arguments.get<JS::Console::Trace>();
+        StringBuilder html;
+        if (!trace.label.is_empty())
+            html.appendff("<span class='title'>{}</span><br>", escape_html_entities(trace.label));
+
+        html.append("<span class='trace'>");
+        for (auto& function_name : trace.stack)
+            html.appendff("-> {}<br>", escape_html_entities(function_name));
+        html.append("</span>");
+
+        print_html(html.string_view());
+        return JS::js_undefined();
+    }
+
+    auto output = String::join(" ", arguments.get<Vector<JS::Value>>());
     m_console.output_debug_message(log_level, output);
 
     StringBuilder html;

Userland/Services/WebContent/WebContentConsoleClient.h

@@ -25,8 +25,7 @@ public:
 
 private:
     virtual void clear() override;
-    virtual JS::Value trace() override;
-    virtual JS::ThrowCompletionOr<JS::Value> printer(JS::Console::LogLevel log_level, Vector<JS::Value>&) override;
+    virtual JS::ThrowCompletionOr<JS::Value> printer(JS::Console::LogLevel log_level, Variant<Vector<JS::Value>, JS::Console::Trace>) override;
 
     ClientConnection& m_client;
     WeakPtr<JS::Interpreter> m_interpreter;

Userland/Utilities/js.cpp

@@ -1128,21 +1128,22 @@ public:
         fflush(stdout);
     }
 
-    virtual JS::Value trace() override
+    virtual JS::ThrowCompletionOr<JS::Value> printer(JS::Console::LogLevel log_level, Variant<Vector<JS::Value>, JS::Console::Trace> arguments) override
     {
-        js_outln("{}", vm().join_arguments());
-        auto trace = get_trace();
-        for (auto& function_name : trace) {
-            if (function_name.is_empty())
-                function_name = "<anonymous>";
-            js_outln(" -> {}", function_name);
-        }
-        return JS::js_undefined();
-    }
+        if (log_level == JS::Console::LogLevel::Trace) {
+            auto trace = arguments.get<JS::Console::Trace>();
+            StringBuilder builder;
+            if (!trace.label.is_empty())
+                builder.appendff("\033[36;1m{}\033[0m\n", trace.label);
 
-    virtual JS::ThrowCompletionOr<JS::Value> printer(JS::Console::LogLevel log_level, Vector<JS::Value>& arguments) override
-    {
-        auto output = String::join(" ", arguments);
+            for (auto& function_name : trace.stack)
+                builder.appendff("-> {}\n", function_name);
+
+            js_outln("{}", builder.string_view());
+            return JS::js_undefined();
+        }
+
+        auto output = String::join(" ", arguments.get<Vector<JS::Value>>());
         m_console.output_debug_message(log_level, output);
 
         switch (log_level) {