LibJS: Consolidate exception function names and source ranges

Instead of storing the function names (in a badly named Vector<String>)
and source ranges separately, consolidate them into a new struct:
TracebackFrame. This makes it both easier to use now and easier to
extend in the future.
Unlike before we now keep each call frame's current node source range
in the traceback frame next to the function name, meaning we can display
line and column numbers outside of the VM and after the call stack is
emptied.

Userland/Applications/Spreadsheet/CellSyntaxHighlighter.cpp

@@ -35,7 +35,8 @@ void CellSyntaxHighlighter::rehighlight(const Palette& palette)
         false);
 
     if (m_cell && m_cell->exception()) {
-        auto range = m_cell->exception()->source_ranges().first();
+        auto& traceback = m_cell->exception()->traceback();
+        auto& range = traceback.first().source_range;
         GUI::TextRange text_range { { range.start.line - 1, range.start.column }, { range.end.line - 1, range.end.column - 1 } };
         m_client->spans().prepend(
             GUI::TextDocumentSpan {

Userland/Applications/Spreadsheet/Spreadsheet.cpp

@@ -55,10 +55,13 @@ Sheet::Sheet(Workbook& workbook)
             parser.print_errors();
         } else {
             interpreter().run(global_object(), parser.parse_program());
-            if (auto exc = interpreter().exception()) {
-                warnln("Spreadsheet: Failed to run runtime code: ");
-                for (auto& t : exc->trace())
-                    warnln("{}", t);
+            if (auto* exception = interpreter().exception()) {
+                warnln("Spreadsheet: Failed to run runtime code:");
+                for (auto& traceback_frame : exception->traceback()) {
+                    auto& function_name = traceback_frame.function_name;
+                    auto& source_range = traceback_frame.source_range;
+                    dbgln("  {} at {}:{}:{}", function_name, source_range.filename, source_range.start.line, source_range.start.column);
+                }
                 interpreter().vm().clear_exception();
             }
         }

Userland/Libraries/LibJS/Runtime/Exception.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Linus Groh <mail@linusgroh.de>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -16,23 +17,16 @@ Exception::Exception(Value value)
     : m_value(value)
 {
     auto& vm = this->vm();
-    auto& call_stack = vm.call_stack();
-    for (ssize_t i = call_stack.size() - 1; i >= 0; --i) {
-        String function_name = call_stack[i]->function_name;
+    m_traceback.ensure_capacity(vm.call_stack().size());
+    for (auto* call_frame : vm.call_stack()) {
+        auto function_name = call_frame->function_name;
         if (function_name.is_empty())
             function_name = "<anonymous>";
-        m_trace.append(function_name);
+        m_traceback.prepend({
+            .function_name = move(function_name),
+            .source_range = call_frame->current_node->source_range(),
+        });
     }
-
-    if (auto* interpreter = vm.interpreter_if_exists()) {
-        for (auto* node_chain = interpreter->executing_ast_node_chain(); node_chain; node_chain = node_chain->previous) {
-            m_source_ranges.append(node_chain->node.source_range());
-        }
-    }
-}
-
-Exception::~Exception()
-{
 }
 
 void Exception::visit_edges(Visitor& visitor)

Userland/Libraries/LibJS/Runtime/Exception.h

@@ -1,11 +1,13 @@
 /*
  * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Linus Groh <mail@linusgroh.de>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #pragma once
 
+#include <AK/FlyString.h>
 #include <AK/Vector.h>
 #include <LibJS/Runtime/Cell.h>
 #include <LibJS/Runtime/Value.h>
@@ -13,22 +15,25 @@
 
 namespace JS {
 
+struct TracebackFrame {
+    FlyString function_name;
+    SourceRange source_range;
+};
+
 class Exception : public Cell {
 public:
     explicit Exception(Value);
-    virtual ~Exception() override;
+    virtual ~Exception() override = default;
 
     Value value() const { return m_value; }
-    const Vector<String>& trace() const { return m_trace; }
-    const Vector<SourceRange>& source_ranges() const { return m_source_ranges; }
+    const Vector<TracebackFrame>& traceback() const { return m_traceback; }
 
 private:
     virtual const char* class_name() const override { return "Exception"; }
     virtual void visit_edges(Visitor&) override;
 
     Value m_value;
-    Vector<String> m_trace;
-    Vector<SourceRange> m_source_ranges;
+    Vector<TracebackFrame> m_traceback;
 };
 
 }

Userland/Utilities/js.cpp

@@ -489,24 +489,27 @@ static bool parse_and_run(JS::Interpreter& interpreter, const StringView& source
         vm->clear_exception();
         out("Uncaught exception: ");
         print(exception->value());
-        auto& trace = exception->trace();
-        if (trace.size() > 1) {
+        auto& traceback = exception->traceback();
+        if (traceback.size() > 1) {
             unsigned repetitions = 0;
-            for (size_t i = 0; i < trace.size(); ++i) {
-                auto& function_name = trace[i];
-                if (i + 1 < trace.size() && trace[i + 1] == function_name) {
-                    repetitions++;
-                    continue;
+            for (size_t i = 0; i < traceback.size(); ++i) {
+                auto& traceback_frame = traceback[i];
+                if (i + 1 < traceback.size()) {
+                    auto& next_traceback_frame = traceback[i + 1];
+                    if (next_traceback_frame.function_name == traceback_frame.function_name) {
+                        repetitions++;
+                        continue;
+                    }
                 }
                 if (repetitions > 4) {
                     // If more than 5 (1 + >4) consecutive function calls with the same name, print
                     // the name only once and show the number of repetitions instead. This prevents
                     // printing ridiculously large call stacks of recursive functions.
-                    outln(" -> {}", function_name);
+                    outln(" -> {}", traceback_frame.function_name);
                     outln(" {} more calls", repetitions);
                 } else {
                     for (size_t j = 0; j < repetitions + 1; ++j)
-                        outln(" -> {}", function_name);
+                        outln(" -> {}", traceback_frame.function_name);
                 }
                 repetitions = 0;
             }