[improv_serial] Support non-Wi-Fi network interfaces (#17598)

Co-authored-by: J. Nick Koston <nick@koston.org>

tests/components/improv_serial/common-ethernet.yaml

@@ -0,0 +1,17 @@
+ethernet:
+  type: W5500
+  clk_pin: 19
+  mosi_pin: 21
+  miso_pin: 17
+  cs_pin: 18
+  interrupt_pin: 36
+  reset_pin: 12
+  clock_speed: 10Mhz
+
+logger:
+  hardware_uart: UART0
+
+# Exercises the per-interface webserver URL collection at compile time
+web_server:
+
+improv_serial:

tests/components/improv_serial/test-ethernet.esp32-idf.yaml

@@ -0,0 +1,2 @@
+packages:
+  improv_serial: !include common-ethernet.yaml

tests/integration/fixtures/external_components/wifi/wifi_component.cpp

@@ -29,6 +29,8 @@ void WiFiComponent::set_sta(const WiFiAP &ap) { ESP_LOGI(TAG, "set_sta ssid=%s",
 
 void WiFiComponent::start_connecting(const WiFiAP &ap) {
   ESP_LOGI(TAG, "start_connecting ssid=%s", ap.get_ssid().c_str());
+  // Connecting succeeds immediately, so the requested network is the connected one
+  this->connected_ssid_ = ap.get_ssid().c_str();
 }
 
 void WiFiComponent::clear_sta() { ESP_LOGI(TAG, "clear_sta"); }

tests/integration/fixtures/external_components/wifi/wifi_component.h

@@ -13,11 +13,15 @@
 #include "esphome/core/component.h"
 #include "esphome/core/string_ref.h"
 
+#include <cstdio>
+#include <span>
 #include <string>
 #include <vector>
 
 namespace esphome::wifi {
 
+static constexpr size_t SSID_BUFFER_SIZE = 33;
+
 class WiFiAP {
  public:
   void set_ssid(const char *ssid) { this->ssid_ = ssid; }
@@ -58,6 +62,12 @@ class WiFiComponent : public Component {
   bool is_disabled() const { return false; }
   // Always connected so network::is_connected() keeps the API server accepting clients
   bool is_connected() const { return true; }
+  // Reports the network start_connecting() was last asked for, so a consumer checking that it
+  // joined the network it requested (rather than an earlier one) sees the connect succeed
+  const char *wifi_ssid_to(std::span<char, SSID_BUFFER_SIZE> buffer) {
+    snprintf(buffer.data(), buffer.size(), "%s", this->connected_ssid_.c_str());
+    return buffer.data();
+  }
   void start_scanning();
   const std::vector<WiFiScanResult> &get_scan_result() const { return this->scan_result_; }
   void set_sta(const WiFiAP &ap);
@@ -70,6 +80,7 @@ class WiFiComponent : public Component {
 
  protected:
   std::vector<WiFiScanResult> scan_result_;
+  std::string connected_ssid_;
 };
 
 extern WiFiComponent *global_wifi_component;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)