Reviewed 4 of 9 files at r1, 5 of 5 files at r2.
Reviewable status: all files reviewed, 6 unresolved discussions (waiting on @markdroth)

src/core/ext/xds/xds_api.cc, line 347 at r2 (raw file):

  // If the same best matched domain pattern appears in multiple virtual hosts,
  // the first matched virtual host wins.
  VirtualHost* target_vhost = nullptr;

why not keep the const?

src/core/ext/xds/xds_api.cc, line 352 at r2 (raw file):

  // Check each domain pattern in each virtual host to determine the best
  // matched virtual host.
  for (VirtualHost& vhost : virtual_hosts) {

why not keep the const?

src/core/ext/xds/xds_api.cc, line 1755 at r2 (raw file):

    grpc_error* error =
        RouteConfigParse(client, tracer, route_config, &rds_update);
    if (error != GRPC_ERROR_NONE) return error;

The logic here changed a bit: if there is a parsing error, the entry is still already added to rds_update_map; whereas before it's only added after parsing is successful.

This is true for Route, and Cds and Eds below

src/core/ext/xds/xds_client.cc, line 908 at r2 (raw file):

    }
    // Ignore identical update.
    ListenerState& listener_state = xds_client()->listener_map_[listener_name];

use fine here? so we don't add an entry with no value?

src/core/ext/xds/xds_client.cc, line 983 at r2 (raw file):

    }
    RouteConfigState& route_config_state =
        xds_client()->route_config_map_[route_config_name];

use find?

src/core/ext/xds/xds_client.cc, line 1105 at r2 (raw file):

    }
    EndpointState& endpoint_state =
        xds_client()->endpoint_map_[eds_service_name];

use find?

Reviewable status: all files reviewed, 6 unresolved discussions (waiting on @donnadionne)

src/core/ext/xds/xds_api.cc, line 347 at r2 (raw file):

Making this method return non-const allows us to use std::move() in xds_resolver.cc line 517.

src/core/ext/xds/xds_api.cc, line 352 at r2 (raw file):

See above.

src/core/ext/xds/xds_api.cc, line 1755 at r2 (raw file):

That's true, but it doesn't matter, because the result will be ignored when we return an error anyway.

src/core/ext/xds/xds_client.cc, line 908 at r2 (raw file):

The entry will always already exist at this point, because XdsApi::ParseAdsResponse() won't return any resources that we are not subscribed to.

src/core/ext/xds/xds_client.cc, line 983 at r2 (raw file):

See above.

src/core/ext/xds/xds_client.cc, line 1105 at r2 (raw file):

See above.

Reviewable status: 6 of 9 files reviewed, all discussions resolved (waiting on @donnadionne)