Replace fixed DSL fields with parameterized metric expressions

app/routes.py

@@ -35,6 +35,7 @@ from .services import activity_data, import_cache, import_upload, route_data
 from .stats import DEFAULT, METRICS, explore, parse_query, period_bounds, query_text
 from .stats_analysis import EXTRA_UNITS, FUNCTIONS, GROUPS
 from .stats_dsl import UNITS
+from .stats_expressions import FUNCTIONS as METRIC_FUNCTIONS
 
 web = Blueprint("web", __name__)
 DUMMY_HASH = generate_password_hash("not-a-real-account-password")
@@ -241,6 +242,7 @@ def stats():
         presets=PRESETS,
         language={
             "functions": sorted(FUNCTIONS),
+            "metric_functions": METRIC_FUNCTIONS,
             "groups": sorted(GROUPS),
             "fields": {
                 key: {