fix: improve exception formatting (#146) (#363)

* fix: fall back to exception class name when string representation is empty (#146)

* fix: walk stacktrace and causal chain to extract exception details in format_exception

* fix: fall back to complete stacktrace when exception has no message, as suggested by maintainer

* fix: address maintainer review, push newline control to printing boundaries

src/heretic/main.py

@@ -69,6 +69,7 @@ from .reproduce import collect_reproducibles
 from .system import empty_cache, get_accelerator_info
 from .utils import (
     format_duration,
+    format_exception,
     get_readme_intro,
     get_trial_parameters,
     is_hf_path,
@@ -364,7 +365,11 @@ def run():
                     # We cannot recover from this.
                     raise
 
-                print(f"[red]Failed[/] ({error})")
+                formatted = format_exception(error)
+                if "\n" in formatted:
+                    print(f"[red]Failed[/]:\n{formatted}")
+                else:
+                    print(f"[red]Failed[/] ({formatted})")
                 break
 
             response_lengths = [
@@ -1120,7 +1125,11 @@ def run():
                                 print(table)
 
                 except Exception as error:
-                    print(f"[red]Error: {error}[/]")
+                    formatted = format_exception(error)
+                    if "\n" in formatted:
+                        print(f"[red]Error:[/]\n{formatted}")
+                    else:
+                        print(f"[red]Error: {formatted}[/]")
 
 
 def main():

src/heretic/model.py

@@ -33,7 +33,7 @@ from transformers.generation import (
 
 from .config import QuantizationMethod, RowNormalization, Settings
 from .system import empty_cache
-from .utils import Prompt, batchify, print
+from .utils import Prompt, batchify, format_exception, print
 
 
 def get_model_class(
@@ -150,7 +150,11 @@ class Model:
             except Exception as error:
                 self.model = None  # ty:ignore[invalid-assignment]
                 empty_cache()
-                print(f"* [red]Failed[/] ({error})")
+                formatted = format_exception(error)
+                if "\n" in formatted:
+                    print(f"* [red]Failed[/]:\n{formatted}")
+                else:
+                    print(f"* [red]Failed[/] ({formatted})")
                 continue
 
             if settings.quantization == QuantizationMethod.BNB_4BIT:

src/heretic/utils.py

@@ -7,6 +7,7 @@ import os
 import platform
 import random
 import tempfile
+import traceback
 from dataclasses import dataclass
 from datetime import datetime, timezone
 from importlib.metadata import version
@@ -746,3 +747,16 @@ def upload_reproduce_folder(
                     repo_id=repo_id,
                     token=token,
                 )
+
+
+def format_exception(error: Exception) -> str:
+    # Walk causal chain to find a non-empty message.
+    current = error
+    while current is not None:
+        message = str(current).strip()
+        if message:
+            return message
+        current = current.__cause__ or current.__context__
+
+    # If there is no message in the entire causal chain, fall back to the complete traceback.
+    return traceback.format_exc().strip()