Reduce verbosity of error messages when concretizing environments (#26843)

With this commit stacktraces of subprocesses are shown only if debug mode is active

lib/spack/spack/environment/environment.py

@@ -1161,7 +1161,8 @@ def _concretize_separately(self, tests=False):
         tty.msg(msg)
 
         concretized_root_specs = spack.util.parallel.parallel_map(
-            _concretize_task, arguments, max_processes=max_processes
+            _concretize_task, arguments, max_processes=max_processes,
+            debug=tty.is_debug()
         )
 
         finish = time.time()

lib/spack/spack/util/parallel.py

@@ -10,8 +10,6 @@
 import sys
 import traceback
 
-import six
-
 from .cpus import cpus_available
 
 
@@ -28,11 +26,16 @@ def __init__(self, exc_cls, exc, tb):
             exc: exception raised from the worker process
         """
         self.pid = os.getpid()
-        self.error_message = ''.join(traceback.format_exception(exc_cls, exc, tb))
+        self.error_message = str(exc)
+        self.stacktrace_message = ''.join(traceback.format_exception(exc_cls, exc, tb))
+
+    @property
+    def stacktrace(self):
+        msg = "[PID={0.pid}] {0.stacktrace_message}"
+        return msg.format(self)
 
     def __str__(self):
-        msg = "[PID={0.pid}] {0.error_message}"
+        return self.error_message
-        return msg.format(self)
 
 
 class Task(object):
@@ -53,29 +56,31 @@ def __call__(self, *args, **kwargs):
         return value
 
 
-def raise_if_errors(*results):
+def raise_if_errors(*results, **kwargs):
     """Analyze results from worker Processes to search for ErrorFromWorker
     objects. If found print all of them and raise an exception.
 
     Args:
         *results: results from worker processes
+        debug: if True show complete stacktraces
 
     Raise:
         RuntimeError: if ErrorFromWorker objects are in the results
     """
-    err_stream = six.StringIO()  # sys.stderr
+    debug = kwargs.get('debug', False)  # This can be a keyword only arg in Python 3
     errors = [x for x in results if isinstance(x, ErrorFromWorker)]
     if not errors:
         return
 
-    # Report the errors and then raise
+    msg = '\n'.join([
-    for error in errors:
+        error.stacktrace if debug else str(error) for error in errors
-        print(error, file=err_stream)
+    ])
 
-    print('[PARENT PROCESS]:', file=err_stream)
+    error_fmt = '{0}'
-    traceback.print_stack(file=err_stream)
+    if len(errors) > 1 and not debug:
-    error_msg = 'errors occurred in worker processes:\n{0}'
+        error_fmt = 'errors occurred during concretization of the environment:\n{0}'
-    raise RuntimeError(error_msg.format(err_stream.getvalue()))
+
+    raise RuntimeError(error_fmt.format(msg))
 
 
 @contextlib.contextmanager
@@ -108,13 +113,15 @@ def num_processes(max_processes=None):
     return min(cpus_available(), max_processes)
 
 
-def parallel_map(func, arguments, max_processes=None):
+def parallel_map(func, arguments, max_processes=None, debug=False):
     """Map a task object to the list of arguments, return the list of results.
 
     Args:
         func (Task): user defined task object
         arguments (list): list of arguments for the task
         max_processes (int or None): maximum number of processes allowed
+        debug (bool): if False, raise an exception containing just the error messages
+            from workers, if True an exception with complete stacktraces
 
     Raises:
         RuntimeError: if any error occurred in the worker processes
@@ -125,5 +132,5 @@ def parallel_map(func, arguments, max_processes=None):
             results = p.map(task_wrapper, arguments)
     else:
         results = list(map(task_wrapper, arguments))
-    raise_if_errors(*results)
+    raise_if_errors(*results, debug=debug)
     return results