pch: fix template and direct-include fallout in non-PCH users

Adjust follow-on fallout from the broader PCH changes:
- remove the redundant scheduling_group std::equal_to specialization from
  lang/wasm_instance_cache.cc
- exclude small test link sets from PCH use in configure.py
- add direct includes at files that no longer get needed declarations
  transitively

configure.py

@@ -2769,6 +2769,25 @@ def write_build_file(f,
             f.write('build {}: rust_source {}\n'.format(cc, src))
             obj = cc.replace('.cc', '.o')
             compiles[obj] = cc
+        # Sources shared between scylla (compiled with PCH) and small tests
+        # (with custom deps and partial link sets) must not use the PCH,
+        # because -fpch-instantiate-templates injects symbol references that
+        # the small test link sets cannot satisfy.
+        small_test_srcs = set()
+        for test_binary, test_deps in deps.items():
+            if not test_binary.startswith('test/'):
+                continue
+            # Only exclude PCH for tests with truly small/partial link sets.
+            # Tests that include scylla_core or similar large dep sets link
+            # against enough objects to satisfy PCH-injected symbol refs.
+            if len(test_deps) > 50:
+                continue
+            for src in test_deps:
+                if src.endswith('.cc'):
+                    small_test_srcs.add(src)
+        for src in small_test_srcs:
+            obj = '$builddir/' + mode + '/' + src.replace('.cc', '.o')
+            compiles_with_pch.discard(obj)
         for obj in compiles:
             src = compiles[obj]
             seastar_dep = f'$builddir/{mode}/seastar/libseastar.{seastar_lib_ext}'

lang/wasm_instance_cache.cc

@@ -284,14 +284,3 @@ future<> instance_cache::stop() {
 }
 
 }
-
-namespace std {
-
-template <>
-struct equal_to<seastar::scheduling_group> {
-    bool operator()(seastar::scheduling_group& sg1, seastar::scheduling_group& sg2) const noexcept {
-        return sg1 == sg2;
-    }
-};
-
-}

service/raft/discovery.hh

@@ -6,6 +6,7 @@
  * SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.1
  */
 #pragma once
+#include <unordered_set>
 #include "service/raft/group0_fwd.hh"
 
 namespace service {

service/raft/group0_fwd.hh

@@ -9,6 +9,10 @@
 #pragma once
 
 #include <iosfwd>
+#include <variant>
+#include <vector>
+#include <seastar/core/timer.hh>
+#include <seastar/core/lowres_clock.hh>
 #include "raft/raft_fwd.hh"
 #include "gms/inet_address.hh"
 

stdafx.hh

@@ -421,6 +421,7 @@
 #include "locator/types.hh"
 #include "mutation/mutation_fragment.hh"
 #include "mutation/mutation_partition.hh"
+#include "replica/database.hh"
 #include "schema/schema.hh"
 #include "schema/schema_builder.hh"
 #include "schema/schema_fwd.hh"

test/boost/commitlog_cleanup_test.cc

@@ -11,6 +11,7 @@
 #undef SEASTAR_TESTING_MAIN
 #include <seastar/testing/test_case.hh>
 #include "test/lib/cql_test_env.hh"
+#include "transport/messages/result_message.hh"
 #include "db/commitlog/commitlog_replayer.hh"
 #include "db/commitlog/commitlog.hh"
 #include "db/config.hh"

test/boost/per_partition_rate_limit_test.cc

@@ -9,6 +9,7 @@
 
 #include "mutation/mutation.hh"
 #include "service/storage_proxy.hh"
+#include "cql3/selection/selection.hh"
 
 BOOST_AUTO_TEST_SUITE(per_partition_rate_limit_test)
 

test/boost/schema_change_test.cc

@@ -18,6 +18,8 @@
 
 #include "test/lib/cql_test_env.hh"
 #include "test/lib/cql_assertions.hh"
+#include "transport/messages/result_message.hh"
+#include "cql3/result_set.hh"
 #include "service/migration_manager.hh"
 #include "service/storage_proxy.hh"
 #include "schema/schema_builder.hh"

test/boost/tablets_test.cc

@@ -18,6 +18,7 @@
 #include "test/lib/random_utils.hh"
 #include "service/topology_mutation.hh"
 #include "service/storage_service.hh"
+#include "gms/gossiper.hh"
 #include <fmt/ranges.h>
 #include <seastar/testing/thread_test_case.hh>
 #include <seastar/testing/on_internal_error.hh>

test/perf/perf_generic_server.cc

@@ -11,6 +11,8 @@
 #include <seastar/coroutine/parallel_for_each.hh>
 #include <seastar/core/temporary_buffer.hh>
 #include <seastar/net/socket_defs.hh>
+#include <seastar/net/api.hh>
+#include <seastar/core/seastar.hh>
 #include <seastar/core/future.hh>
 #include <seastar/core/shared_ptr.hh>
 #include <seastar/core/thread.hh>

test/vector_search/rescoring_test.cc

@@ -14,6 +14,7 @@
 #include "vector_search/vector_store_client.hh"
 #include "vs_mock_server.hh"
 #include "test/lib/cql_test_env.hh"
+#include "transport/messages/result_message.hh"
 #include "utils/rjson.hh"
 #include <boost/test/tools/old/interface.hpp>
 #include <seastar/core/seastar.hh>