[socket] Compile the lookup and client link helpers only when required (#20002)

tests/unit_tests/components/socket/test_socket_source_filter.py

@@ -0,0 +1,38 @@
+"""Tests for the socket component's source filtering and require functions."""
+
+from unittest.mock import patch
+
+from esphome.components import socket
+from esphome.core import Define
+
+
+def test_helper_files_filtered_until_required() -> None:
+    """ipv4_resolve.cpp and tcp_client_link.cpp compile only when required."""
+    with patch("esphome.config_helpers.CORE") as mock_core:
+        mock_core.defines = set()
+        filtered = socket.FILTER_SOURCE_FILES()
+        assert "ipv4_resolve.cpp" in filtered
+        assert "tcp_client_link.cpp" in filtered
+
+        mock_core.defines = {Define("USE_SOCKET_IPV4_RESOLVE")}
+        filtered = socket.FILTER_SOURCE_FILES()
+        assert "ipv4_resolve.cpp" not in filtered
+        assert "tcp_client_link.cpp" in filtered
+
+        mock_core.defines = {
+            Define("USE_SOCKET_IPV4_RESOLVE"),
+            Define("USE_SOCKET_TCP_CLIENT_LINK"),
+        }
+        filtered = socket.FILTER_SOURCE_FILES()
+        assert "ipv4_resolve.cpp" not in filtered
+        assert "tcp_client_link.cpp" not in filtered
+
+
+def test_require_tcp_client_link_pulls_in_the_resolver() -> None:
+    """require_tcp_client_link() sets both defines; the link reads the resolver."""
+    with patch.object(socket.cg, "add_define") as add_define:
+        socket.require_tcp_client_link()
+    assert {call.args[0] for call in add_define.call_args_list} == {
+        "USE_SOCKET_IPV4_RESOLVE",
+        "USE_SOCKET_TCP_CLIENT_LINK",
+    }