Bug 1636251: document mach error reporting r=rstewart

Differential Revision: https://phabricator.services.mozilla.com/D78409

build/docs/telemetry.rst

@@ -6,10 +6,15 @@ Build Telemetry
 
 The build system (specifically, all the build tooling hooked
 up to ``./mach``) has been configured to collect metrics data
-points for various build system actions. This data helps drive
-team planning for the build team and ensure that resources are
-applied to build processes that need them most. You can opt-in
-to send telemetry to Mozilla during `./mach bootstrap`.
+points and errors for various build system actions. This data
+helps drive team planning for the build team and ensure that
+resources are applied to build processes that need them most.
+You can opt-in to send telemetry to Mozilla during
+``./mach bootstrap`` or by editing your ``.mozbuild/machrc``
+file.
+
+Telemetry
+=========
 
 The build telemetry schema can be found in-tree under
 ``python/mozbuild/mozbuild/telemetry.py`` in Voluptuous schema
@@ -17,13 +22,8 @@ format. You can use the ``export_telemetry_schema.py`` script in
 that same directory to get the schema in JSON-schema format.
 Details of the schema are specified below:
 
-
-
 .. _telemetry.json#/:
 
-telemetry
-=========
-
 :type: ``object``
 
 :Required: :ref:`telemetry.json#/properties/argv`, :ref:`telemetry.json#/properties/build_opts`, :ref:`telemetry.json#/properties/client_id`, :ref:`telemetry.json#/properties/command`, :ref:`telemetry.json#/properties/duration_ms`, :ref:`telemetry.json#/properties/success`, :ref:`telemetry.json#/properties/system`, :ref:`telemetry.json#/properties/time`
@@ -351,3 +351,34 @@ Time at which this event happened
 :type: ``string``
 
 :format: ``date-time``
+
+
+Error Reporting
+===============
+
+``./mach`` uses `Sentry <https://sentry.io/welcome/>`_
+to automatically report errors to `our issue-tracking dashboard
+<https://sentry.prod.mozaws.net/operations/mach/>`_.
+
+Information captured
+++++++++++++++++++++
+
+Sentry automatically collects useful information surrounding
+the error to help the build team discover what caused the
+issue and how to reproduce it. This information includes:
+
+* Environmental information, such as the computer name, timestamp, Python runtime and Python module versions
+* Process arguments
+* The stack trace of the error, including contextual information:
+
+    * The data contained in the exception
+    * Functions and their respective source file names, line numbers
+    * Variables in each frame
+* `Sentry "Breadcrumbs" <https://docs.sentry.io/platforms/python/default-integrations/>`_,
+  which are important events that have happened which help contextualize the error, such as:
+
+    * An HTTP request has occurred
+    * A subprocess has been spawned
+    * Logging has occurred
+
+Note that file paths may be captured, which include absolute paths (potentially including usernames).