Bug 1646406 - Distinguish between user errors and actual reportable exceptions in `mach` r=mhentges,froydnj

Add a new `UserError` class which when thrown doesn't get reported to Sentry.

Differential Revision: https://phabricator.services.mozilla.com/D85026

python/mach/mach/main.py

@@ -37,7 +37,7 @@ from .dispatcher import CommandAction
 from .logging import LoggingManager
 from .registrar import Registrar
 from .sentry import register_sentry, NoopErrorReporter
-from .util import setenv
+from .util import setenv, UserError
 
 SUGGEST_MACH_BUSTED_TEMPLATE = r'''
 You can invoke |./mach busted| to check if this issue is already on file. If it
@@ -58,6 +58,10 @@ message.
 The details of the failure are as follows:
 '''.lstrip()
 
+USER_ERROR = r'''
+This is a user error and does not appear to be a bug in mach.
+'''.lstrip()
+
 COMMAND_ERROR_TEMPLATE = r'''
 The error occurred in the implementation of the invoked mach command.
 
@@ -483,6 +487,15 @@ To see more help for a specific command, run:
         except FailedCommandError as e:
             print(e.message)
             return e.exit_code
+        except UserError:
+            # We explicitly don't report UserErrors to Sentry.
+            exc_type, exc_value, exc_tb = sys.exc_info()
+            # The first two frames are us and are never used.
+            stack = traceback.extract_tb(exc_tb)[2:]
+            self._print_error_header(argv, sys.stdout)
+            print(USER_ERROR)
+            self._print_exception(sys.stdout, exc_type, exc_value, stack)
+            return 1
         except Exception:
             exc_type, exc_value, exc_tb = sys.exc_info()
             sentry.report_exception(exc_value)

python/mach/mach/util.py

@@ -10,6 +10,13 @@ import sys
 from six import text_type
 
 
+class UserError(Exception):
+    """Represents an error caused by something the user did wrong rather than
+    an internal `mach` failure. Exceptions that are subclasses of this class
+    will not be reported as failures to Sentry.
+    """
+
+
 def setenv(key, value):
     """Compatibility shim to ensure the proper string type is used with
     os.environ for the version of Python being used.