Show traceback of exception in output area

media/programflow-visualization/webview.css

@@ -188,3 +188,7 @@ body {
 .return-value {
   color: blue;
 }
+
+.traceback-text {
+  color: red;
+}

pytrace-generator/main.py

@@ -10,6 +10,7 @@
 import re
 import socket
 import sys
+import traceback
 import types
 import typing
 
@@ -253,15 +254,19 @@ class TraceStep:
     stack: Stack
     heap: Heap
     stdout: str
+    traceback_text: str
 
     def format(self):
-        return {
+        step = {
             "line": self.line,
             "filePath": self.file_path,
             "stack": self.stack.format(),
             "heap": self.heap.format(),
             "stdout": self.stdout,
         }
+        if self.traceback_text is not None:
+            step["traceback"] = self.traceback_text
+        return step
 
 
 def should_ignore(variable_name, value, script_path, ignore_list = []):
@@ -377,7 +382,8 @@ def trace_dispatch(self, frame, event, arg):
         self.import_following = import_regex.search(next_source_line) is not None
 
         display_return = event == "return" and self.last_event != "exception" and len(self.stack.frames) > 1
-        if event == "line" or display_return:
+        display_exception = event == "exception" and self.last_event != "return"
+        if event == "line" or display_return or display_exception:
             for variable_name in frame.f_locals:
                 if should_ignore_on_stack(variable_name, frame.f_locals[variable_name], self.filename, self.stack_ignore):
                     continue
@@ -389,7 +395,15 @@ def trace_dispatch(self, frame, event, arg):
                 heap = generate_heap(frame, self.filename, self.stack_ignore)
             accumulated_stdout = self.accumulated_stdout + self.captured_stdout.getvalue()
 
-            step = TraceStep(line, filename, copy.deepcopy(self.stack), copy.deepcopy(heap), accumulated_stdout)
+            traceback_text = None
+            if event == "exception":
+                exception_value = arg[1]
+                traceback_text_tmp = io.StringIO()
+                traceback.print_exception(exception_value, limit=0, file=traceback_text_tmp)
+                traceback_text = traceback_text_tmp.getvalue()
+
+
+            step = TraceStep(line, filename, copy.deepcopy(self.stack), copy.deepcopy(heap), accumulated_stdout, traceback_text)
 
             is_annotation = next_source_line.startswith("@")
             should_display_step = not is_annotation
@@ -412,6 +426,10 @@ def trace_dispatch(self, frame, event, arg):
                     self.shown_class_defs.append(filename, line)
                 self.last_step_was_class = is_class_def
                 self.prev_num_frames = num_frames
+
+            if event == "exception":
+                # Terminate visualization after first exception in user code
+                self.set_quit()
         if event == "call":
             self.stack.push_frame(frame)
             self.shown_class_defs.push_frame()

pytrace-generator/test/test-cases/divideByZero.py.json

@@ -276,7 +276,7 @@
 		"stdout": ""
 	},
 	{
-		"line": 11,
+		"line": 3,
 		"filePath": "divideByZero.py",
 		"stack": [
 			{
@@ -288,45 +288,40 @@
 						"name": "bar"
 					}
 				]
-			}
-		],
-		"heap": {},
-		"stdout": ""
-	},
-	{
-		"line": 12,
-		"filePath": "divideByZero.py",
-		"stack": [
+			},
 			{
-				"frameName": "<module>",
+				"frameName": "bar",
 				"locals": [
 					{
-						"type": "function",
-						"value": "<function bar>",
-						"name": "bar"
+						"type": "int",
+						"value": 2,
+						"name": "i"
 					}
 				]
-			}
-		],
-		"heap": {},
-		"stdout": ""
-	},
-	{
-		"line": 14,
-		"filePath": "divideByZero.py",
-		"stack": [
+			},
 			{
-				"frameName": "<module>",
+				"frameName": "bar",
 				"locals": [
 					{
-						"type": "function",
-						"value": "<function bar>",
-						"name": "bar"
+						"type": "int",
+						"value": 1,
+						"name": "i"
+					}
+				]
+			},
+			{
+				"frameName": "bar",
+				"locals": [
+					{
+						"type": "int",
+						"value": 0,
+						"name": "i"
 					}
 				]
 			}
 		],
 		"heap": {},
-		"stdout": ""
+		"stdout": "",
+		"traceback": "ZeroDivisionError: division by zero\n"
 	}
 ]

src/programflow-visualization/frontend/HTMLGenerator.ts

@@ -46,7 +46,11 @@ export class HTMLGenerator {
                 ${keys.map((name, index) => this.objectItem(name, values[index])).join('')}
             <div>
         `;
-        return [traceElement.line, frameItems, objectItems, traceElement.filePath, traceElement.stdout];
+        let output = traceElement.stdout;
+        if (traceElement.traceback !== undefined) {
+            output += `<span class="traceback-text">${traceElement.traceback}</span>`;
+        }
+        return [traceElement.line, frameItems, objectItems, traceElement.filePath, output];
     }
 
     private objectItem(name: string, value: HeapValue): string {

src/programflow-visualization/types.ts

@@ -21,6 +21,7 @@ type BackendTraceElem = {
   stack: Array<StackElem>;
   heap: Map<Address, HeapValue>;
   stdout: string;
+  traceback: string | undefined;
 };
 
 type Address = number;