Bug 1654084 - Log build project to telemetry r=firefox-build-system-reviewers,dmajor

Differential Revision: https://phabricator.services.mozilla.com/D94868

python/mozbuild/metrics.yaml

@@ -120,3 +120,17 @@ mozbuild:
     expires: never
     send_in_pings:
       - usage
+  project:
+    type: string
+    description: The project being built.
+    lifetime: application
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1654084
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1654084#c2
+    notification_emails:
+      - build-telemetry@mozilla.com
+      - mhentges@mozilla.com
+    expires: never
+    send_in_pings:
+      - usage

python/mozbuild/mozbuild/controller/building.py

@@ -1163,6 +1163,7 @@ class BuildDriver(MozbuildObject):
             mozbuild_metrics.ccache.set(get_substs_flag("CCACHE"))
             mozbuild_metrics.sccache.set(get_substs_flag("MOZ_USING_SCCACHE"))
             mozbuild_metrics.icecream.set(get_substs_flag("CXX_IS_ICECREAM"))
+            mozbuild_metrics.project.set(substs.get("MOZ_BUILD_APP", ""))
 
             all_backends = config.substs.get("BUILD_BACKENDS", [None])
             active_backend = all_backends[0]