logger: add DVC_SHOW_TRACEBACK envvar to show traceback on exception (#9310)

This will come useful in debugging, where you don't have to add --verbose just to
see where it failed or go through verbose logs (which might be useful when working
with UI issues as you want to see what the user sees).

Ideally this should be handled in main when we exit with error instead of using
logger.{warning,error,exception} to log exception as the intention is to only log
last exception that makes it exit. But since we don't have that capability and
we don't abuse logging.{warning,error,exception} to log and suppress exceptions, this is a good
enough solution for now without complicating `dvc.cli.main()`.

dvc/env.py

@@ -9,3 +9,4 @@ DVC_EXP_NAME = "DVC_EXP_NAME"
 DVC_EXP_GIT_REMOTE = "DVC_EXP_GIT_REMOTE"
 DVC_EXP_AUTO_PUSH = "DVC_EXP_AUTO_PUSH"
 DVC_NO_ANALYTICS = "DVC_NO_ANALYTICS"
+DVC_SHOW_TRACEBACK = "DVC_SHOW_TRACEBACK"

dvc/logger.py

@@ -3,10 +3,12 @@
 import logging
 import logging.config
 import logging.handlers
+import os
 import sys
 
 import colorama
 
+from dvc.env import DVC_SHOW_TRACEBACK
 from dvc.progress import Tqdm
 
 
@@ -86,9 +88,10 @@ class ColorFormatter(logging.Formatter):
         "CRITICAL": colorama.Fore.RED,
     }
 
-    def __init__(self, log_colors: bool = True) -> None:
+    def __init__(self, log_colors: bool = True, show_traceback: bool = False) -> None:
         super().__init__()
         self.log_colors = log_colors
+        self.show_traceback = show_traceback
 
     def format(self, record) -> str:  # noqa: A003, C901
         record.message = record.getMessage()
@@ -106,8 +109,10 @@ class ColorFormatter(logging.Formatter):
             msg = msg + sep + cause
 
         asctime = ""
-        if _is_verbose():
+        verbose = _is_verbose()
+        if verbose:
             asctime = self.formatTime(record, self.datefmt)
+        if verbose or self.show_traceback:
             if ei and not record.exc_text:
                 record.exc_text = self.formatException(ei)
             if record.exc_text:
@@ -198,7 +203,10 @@ def setup(level: int = logging.INFO, log_colors: bool = True) -> None:
     console_trace.setFormatter(formatter)
     console_trace.addFilter(exclude_filter(logging.DEBUG))
 
-    err_formatter = ColorFormatter(log_colors=log_colors and sys.stderr.isatty())
+    show_traceback = bool(os.environ.get(DVC_SHOW_TRACEBACK))
+    err_formatter = ColorFormatter(
+        log_colors=log_colors and sys.stderr.isatty(), show_traceback=show_traceback
+    )
     console_errors = LoggerHandler(sys.stderr)
     console_errors.setLevel(logging.WARNING)
     console_errors.setFormatter(err_formatter)