CDRIVER-1564 never use PossiblePrimary for query

Author: ajdavis

NEWS

@@ -37,6 +37,7 @@ New features and bug fixes:
   * Added support for the new readConcernLevel "linearizable".
   * New CMake option ENABLE_TRACING allows debug output, which before had only
     been available with "configure --enable-tracing".
+  * Bugfix: "PossiblePrimary"-type replicas could be selected for reads
 
 Removed configure flags:
   * --enable-experimental has been removed and all of its features

src/mongoc/mongoc-topology-description.c

@@ -290,7 +290,6 @@ _mongoc_topology_description_server_is_candidate (
       switch ((int)read_mode) {
       case MONGOC_READ_PRIMARY:
          switch ((int)desc_type) {
-         case MONGOC_SERVER_POSSIBLE_PRIMARY:
          case MONGOC_SERVER_RS_PRIMARY:
             return true;
          default:
@@ -305,7 +304,6 @@ _mongoc_topology_description_server_is_candidate (
          }
       default:
          switch ((int)desc_type) {
-         case MONGOC_SERVER_POSSIBLE_PRIMARY:
          case MONGOC_SERVER_RS_PRIMARY:
          case MONGOC_SERVER_RS_SECONDARY:
             return true;

tests/json/server_selection/server_selection/ReplicaSetNoPrimary/read/PossiblePrimary.json

@@ -0,0 +1,21 @@
+{
+    "in_latency_window": [],
+    "operation": "read",
+    "read_preference": {
+        "mode": "Primary",
+        "tag_sets": [
+            {}
+        ]
+    },
+    "suitable_servers": [],
+    "topology_description": {
+        "servers": [
+            {
+                "address": "b:27017",
+                "avg_rtt_ms": 5,
+                "type": "PossiblePrimary"
+            }
+        ],
+        "type": "ReplicaSetNoPrimary"
+    }
+}

tests/json/server_selection/server_selection/ReplicaSetNoPrimary/read/PossiblePrimaryNearest.json

@@ -0,0 +1,21 @@
+{
+    "in_latency_window": [],
+    "operation": "read",
+    "read_preference": {
+        "mode": "Nearest",
+        "tag_sets": [
+            {}
+        ]
+    },
+    "suitable_servers": [],
+    "topology_description": {
+        "servers": [
+            {
+                "address": "b:27017",
+                "avg_rtt_ms": 5,
+                "type": "PossiblePrimary"
+            }
+        ],
+        "type": "ReplicaSetNoPrimary"
+    }
+}