LibJS: Remove ExecutionContext::function_name field

Instead of having ExecutionContext track function names separately,
we give FunctionObject a virtual function that returns an appropriate
name string for use in call stacks.

Libraries/LibJS/Console.cpp

@@ -350,10 +350,10 @@ ThrowCompletionOr<Value> Console::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 const& function_name = execution_context_stack[i]->function_name;
-        trace.stack.append((!function_name || function_name->is_empty())
+        auto function_name = execution_context_stack[i]->function ? execution_context_stack[i]->function->name_for_call_stack() : ""_utf16;
+        trace.stack.append(function_name.is_empty()
                 ? "<anonymous>"_string
-                : function_name->utf8_string());
+                : function_name.to_utf8());
     }
 
     // 2. Optionally, let formattedData be the result of Formatter(data), and incorporate formattedData as a label for trace.

Libraries/LibJS/Runtime/BoundFunction.cpp

@@ -115,4 +115,9 @@ ThrowCompletionOr<void> BoundFunction::get_stack_frame_size(size_t& registers_an
     return {};
 }
 
+Utf16String BoundFunction::name_for_call_stack() const
+{
+    return m_bound_target_function->name_for_call_stack();
+}
+
 }

Libraries/LibJS/Runtime/BoundFunction.h

@@ -30,6 +30,8 @@ public:
     Value bound_this() const { return m_bound_this; }
     Vector<Value> const& bound_arguments() const { return m_bound_arguments; }
 
+    virtual Utf16String name_for_call_stack() const override;
+
 private:
     BoundFunction(Realm&, FunctionObject& target_function, Value bound_this, Vector<Value> bound_arguments, Object* prototype);
 

Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -694,7 +694,6 @@ void ECMAScriptFunctionObject::prepare_for_ordinary_call(VM& vm, ExecutionContex
 
     // 3. Set the Function of calleeContext to F.
     callee_context.function = this;
-    callee_context.function_name = m_name_string;
 
     // 4. Let calleeRealm be F.[[Realm]].
     // 5. Set the Realm of calleeContext to calleeRealm.
@@ -933,4 +932,9 @@ ECMAScriptFunctionObject::ClassData& ECMAScriptFunctionObject::ensure_class_data
     return *m_class_data;
 }
 
+Utf16String ECMAScriptFunctionObject::name_for_call_stack() const
+{
+    return m_name_string->utf16_string();
+}
+
 }

Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h

@@ -139,6 +139,8 @@ public:
     Statement const& ecmascript_code() const { return *shared_data().m_ecmascript_code; }
     [[nodiscard]] virtual FunctionParameters const& formal_parameters() const override { return *shared_data().m_formal_parameters; }
 
+    virtual Utf16String name_for_call_stack() const override;
+
     Utf16FlyString const& name() const { return shared_data().m_name; }
     void set_name(Utf16FlyString const& name);
 

Libraries/LibJS/Runtime/Error.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Andreas Kling <andreas@ladybird.org>
+ * Copyright (c) 2020-2025, Andreas Kling <andreas@ladybird.org>
  * Copyright (c) 2021-2023, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -10,6 +10,7 @@
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Error.h>
 #include <LibJS/Runtime/ExecutionContext.h>
+#include <LibJS/Runtime/FunctionObject.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/SourceRange.h>
 
@@ -90,7 +91,7 @@ void Error::populate_stack()
     for (auto& element : stack_trace) {
         auto* context = element.execution_context;
         TracebackFrame frame {
-            .function_name = context->function_name ? context->function_name->utf8_string() : ""_string,
+            .function_name = context->function ? context->function->name_for_call_stack() : ""_utf16,
             .cached_source_range = element.source_range,
         };
 
@@ -117,7 +118,7 @@ String Error::stack_string(CompactTraceback compact) const
             else
                 stack_string_builder.appendff("    at {} ({}:{}:{})\n", function_name, source_range.filename(), source_range.start.line, source_range.start.column);
         } else {
-            stack_string_builder.appendff("    at {}\n", function_name.is_empty() ? "<unknown>"sv : function_name);
+            stack_string_builder.appendff("    at {}\n", function_name.is_empty() ? "<unknown>"_utf16 : function_name);
         }
     };
 

Libraries/LibJS/Runtime/Error.h

@@ -18,7 +18,7 @@
 namespace JS {
 
 struct JS_API TracebackFrame {
-    FlyString function_name;
+    Utf16String function_name;
     [[nodiscard]] SourceRange const& source_range() const;
 
     RefPtr<CachedSourceRange> cached_source_range;

Libraries/LibJS/Runtime/ExecutionContext.cpp

@@ -122,7 +122,6 @@ NonnullOwnPtr<ExecutionContext> ExecutionContext::copy() const
     copy->variable_environment = variable_environment;
     copy->private_environment = private_environment;
     copy->program_counter = program_counter;
-    copy->function_name = function_name;
     copy->this_value = this_value;
     copy->executable = executable;
     copy->passed_argument_count = passed_argument_count;
@@ -147,7 +146,6 @@ void ExecutionContext::visit_edges(Cell::Visitor& visitor)
     if (this_value.has_value())
         visitor.visit(*this_value);
     visitor.visit(executable);
-    visitor.visit(function_name);
     visitor.visit(registers_and_constants_and_locals_and_arguments_span());
     for (auto& context : unwind_contexts) {
         visitor.visit(context.lexical_environment);

Libraries/LibJS/Runtime/ExecutionContext.h

@@ -62,7 +62,6 @@ public:
 
     mutable RefPtr<CachedSourceRange> cached_source_range;
 
-    GC::Ptr<PrimitiveString> function_name;
     Optional<Value> this_value;
 
     GC::Ptr<Bytecode::Executable> executable;

Libraries/LibJS/Runtime/FunctionObject.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2021, Andreas Kling <andreas@ladybird.org>
+ * Copyright (c) 2020-2025, Andreas Kling <andreas@ladybird.org>
  * Copyright (c) 2021-2022, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -42,6 +42,8 @@ public:
 
     virtual FunctionParameters const& formal_parameters() const { VERIFY_NOT_REACHED(); }
 
+    virtual Utf16String name_for_call_stack() const = 0;
+
     template<typename T>
     bool fast_is() const = delete;
 

Libraries/LibJS/Runtime/FunctionPrototype.cpp

@@ -192,4 +192,9 @@ JS_DEFINE_NATIVE_FUNCTION(FunctionPrototype::symbol_has_instance)
     return TRY(ordinary_has_instance(vm, vm.argument(0), vm.this_value()));
 }
 
+Utf16String FunctionPrototype::name_for_call_stack() const
+{
+    return "(Function.prototype)"_utf16;
+}
+
 }

Libraries/LibJS/Runtime/FunctionPrototype.h

@@ -20,6 +20,8 @@ public:
 
     virtual ThrowCompletionOr<Value> internal_call(ExecutionContext&, Value this_argument) override;
 
+    virtual Utf16String name_for_call_stack() const override;
+
 private:
     explicit FunctionPrototype(Realm&);
 

Libraries/LibJS/Runtime/NativeFunction.cpp

@@ -123,7 +123,6 @@ ThrowCompletionOr<Value> NativeFunction::internal_call(ExecutionContext& callee_
 
     // 4. Set the Function of calleeContext to F.
     callee_context.function = this;
-    callee_context.function_name = m_name_string;
 
     // 5. Let calleeRealm be F.[[Realm]].
     auto callee_realm = m_realm;
@@ -179,7 +178,6 @@ ThrowCompletionOr<GC::Ref<Object>> NativeFunction::internal_construct(ExecutionC
 
     // 4. Set the Function of calleeContext to F.
     callee_context.function = this;
-    callee_context.function_name = m_name_string;
 
     // 5. Let calleeRealm be F.[[Realm]].
     auto callee_realm = m_realm;
@@ -233,4 +231,9 @@ bool NativeFunction::is_strict_mode() const
     return true;
 }
 
+Utf16String NativeFunction::name_for_call_stack() const
+{
+    return m_name.to_utf16_string();
+}
+
 }

Libraries/LibJS/Runtime/NativeFunction.h

@@ -36,6 +36,8 @@ public:
     virtual ThrowCompletionOr<Value> call();
     virtual ThrowCompletionOr<GC::Ref<Object>> construct(FunctionObject& new_target);
 
+    virtual Utf16String name_for_call_stack() const override;
+
     Utf16FlyString const& name() const { return m_name; }
     virtual bool is_strict_mode() const override;
     virtual bool has_constructor() const override { return false; }

Libraries/LibJS/Runtime/ProxyObject.cpp

@@ -895,4 +895,9 @@ ThrowCompletionOr<void> ProxyObject::get_stack_frame_size(size_t& registers_and_
     return as<FunctionObject>(*m_target).get_stack_frame_size(registers_and_constants_and_locals_count, argument_count);
 }
 
+Utf16String ProxyObject::name_for_call_stack() const
+{
+    return "(Proxy)"_utf16;
+}
+
 }

Libraries/LibJS/Runtime/ProxyObject.h

@@ -46,6 +46,8 @@ public:
     virtual ThrowCompletionOr<GC::Ref<Object>> internal_construct(ExecutionContext&, FunctionObject& new_target) override;
     ThrowCompletionOr<void> validate_non_revoked_proxy() const;
 
+    virtual Utf16String name_for_call_stack() const override;
+
 private:
     ProxyObject(Object& target, Object& handler, Object& prototype);
 

Libraries/LibJS/Runtime/VM.cpp

@@ -483,11 +483,12 @@ void VM::dump_backtrace() const
 {
     for (ssize_t i = m_execution_context_stack.size() - 1; i >= 0; --i) {
         auto& frame = m_execution_context_stack[i];
+
         if (frame->executable) {
             auto source_range = frame->executable->source_range_at(frame->program_counter).realize();
-            dbgln("-> {} @ {}:{},{}", frame->function_name ? frame->function_name->utf8_string() : ""_string, source_range.filename(), source_range.start.line, source_range.start.column);
+            dbgln("-> {} @ {}:{},{}", frame->function ? frame->function->name_for_call_stack() : ""_utf16, source_range.filename(), source_range.start.line, source_range.start.column);
         } else {
-            dbgln("-> {}", frame->function_name ? frame->function_name->utf8_string() : ""_string);
+            dbgln("-> {}", frame->function ? frame->function->name_for_call_stack() : ""_utf16);
         }
     }
 }

Libraries/LibJS/Runtime/WrappedFunction.cpp

@@ -174,4 +174,9 @@ void prepare_for_wrapped_function_call(WrappedFunction& function, ExecutionConte
     // NOTE: No-op, see NOTE after step 2.
 }
 
+Utf16String WrappedFunction::name_for_call_stack() const
+{
+    return "(Wrapped)"_utf16;
+}
+
 }

Libraries/LibJS/Runtime/WrappedFunction.h

@@ -29,6 +29,8 @@ public:
 
     virtual ThrowCompletionOr<void> get_stack_frame_size(size_t& registers_and_constants_and_locals_count, size_t& argument_count) override;
 
+    virtual Utf16String name_for_call_stack() const override;
+
 private:
     WrappedFunction(Realm&, FunctionObject&, Object& prototype);
 

Services/WebContent/DevToolsConsoleClient.cpp

@@ -114,7 +114,7 @@ void DevToolsConsoleClient::report_exception(JS::Error const& exception, bool in
         WebView::StackFrame stack_frame;
 
         if (!frame.function_name.is_empty())
-            stack_frame.function = frame.function_name.to_string();
+            stack_frame.function = frame.function_name.to_utf8();
 
         if (!source_range.filename().is_empty() || source_range.start.offset != 0 || source_range.end.offset != 0) {
             stack_frame.file = String::from_utf8_with_replacement_character(source_range.filename());