[wifi] Use FixedVector for scan results to reduce flash usage (#11216)

esphome/components/improv_serial/improv_serial_component.cpp

@@ -218,7 +218,7 @@ bool ImprovSerialComponent::parse_improv_payload_(improv::ImprovCommand &command
     }
     case improv::GET_WIFI_NETWORKS: {
       std::vector<std::string> networks;
-      auto results = wifi::global_wifi_component->get_scan_result();
+      const auto &results = wifi::global_wifi_component->get_scan_result();
       for (auto &scan : results) {
         if (scan.get_is_hidden())
           continue;

esphome/components/wifi/wifi_component.cpp

@@ -549,7 +549,7 @@ void WiFiComponent::start_scanning() {
 // Using insertion sort instead of std::stable_sort saves flash memory
 // by avoiding template instantiations (std::rotate, std::stable_sort, lambdas)
 // IMPORTANT: This sort is stable (preserves relative order of equal elements)
-static void insertion_sort_scan_results(std::vector<WiFiScanResult> &results) {
+template<typename VectorType> static void insertion_sort_scan_results(VectorType &results) {
   const size_t size = results.size();
   for (size_t i = 1; i < size; i++) {
     // Make a copy to avoid issues with move semantics during comparison

esphome/components/wifi/wifi_component.h

@@ -121,6 +121,14 @@ struct EAPAuth {
 
 using bssid_t = std::array<uint8_t, 6>;
 
+// Use std::vector for RP2040 since scan count is unknown (callback-based)
+// Use FixedVector for other platforms where count is queried first
+#ifdef USE_RP2040
+template<typename T> using wifi_scan_vector_t = std::vector<T>;
+#else
+template<typename T> using wifi_scan_vector_t = FixedVector<T>;
+#endif
+
 class WiFiAP {
  public:
   void set_ssid(const std::string &ssid);
@@ -278,7 +286,7 @@ class WiFiComponent : public Component {
   const std::string &get_use_address() const;
   void set_use_address(const std::string &use_address);
 
-  const std::vector<WiFiScanResult> &get_scan_result() const { return scan_result_; }
+  const wifi_scan_vector_t<WiFiScanResult> &get_scan_result() const { return scan_result_; }
 
   network::IPAddress wifi_soft_ap_ip();
 
@@ -386,7 +394,7 @@ class WiFiComponent : public Component {
   std::string use_address_;
   std::vector<WiFiAP> sta_;
   std::vector<WiFiSTAPriority> sta_priorities_;
-  std::vector<WiFiScanResult> scan_result_;
+  wifi_scan_vector_t<WiFiScanResult> scan_result_;
   WiFiAP selected_ap_;
   WiFiAP ap_;
   optional<float> output_power_;

esphome/components/wifi/wifi_component_esp8266.cpp

@@ -696,7 +696,15 @@ void WiFiComponent::wifi_scan_done_callback_(void *arg, STATUS status) {
     this->retry_connect();
     return;
   }
+
+  // Count the number of results first
   auto *head = reinterpret_cast<bss_info *>(arg);
+  size_t count = 0;
+  for (bss_info *it = head; it != nullptr; it = STAILQ_NEXT(it, next)) {
+    count++;
+  }
+
+  this->scan_result_.init(count);
   for (bss_info *it = head; it != nullptr; it = STAILQ_NEXT(it, next)) {
     WiFiScanResult res({it->bssid[0], it->bssid[1], it->bssid[2], it->bssid[3], it->bssid[4], it->bssid[5]},
                        std::string(reinterpret_cast<char *>(it->ssid), it->ssid_len), it->channel, it->rssi,

esphome/components/wifi/wifi_component_esp_idf.cpp

@@ -784,7 +784,7 @@ void WiFiComponent::wifi_process_event_(IDFWiFiEvent *data) {
     }
     records.resize(number);
 
-    scan_result_.reserve(number);
+    scan_result_.init(number);
     for (int i = 0; i < number; i++) {
       auto &record = records[i];
       bssid_t bssid;

esphome/components/wifi/wifi_component_libretiny.cpp

@@ -411,7 +411,7 @@ void WiFiComponent::wifi_scan_done_callback_() {
   if (num < 0)
     return;
 
-  this->scan_result_.reserve(static_cast<unsigned int>(num));
+  this->scan_result_.init(static_cast<unsigned int>(num));
   for (int i = 0; i < num; i++) {
     String ssid = WiFi.SSID(i);
     wifi_auth_mode_t authmode = WiFi.encryptionType(i);