[ci] Soft-deprecate str_sprintf/str_snprintf to prevent hidden heap allocations

esphome/components/cse7766/cse7766.cpp

@@ -2,7 +2,6 @@
 #include "esphome/core/application.h"
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
-#include <cstdarg>
 
 namespace esphome {
 namespace cse7766 {
@@ -10,32 +9,6 @@ namespace cse7766 {
 static const char *const TAG = "cse7766";
 static constexpr size_t CSE7766_RAW_DATA_SIZE = 24;
 
-#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERY_VERBOSE
-/// @brief Safely append formatted string to buffer.
-/// @param buf Destination buffer (must be non-null)
-/// @param size Total buffer size in bytes
-/// @param pos Current write position (0 to size-1 for valid positions, size means full)
-/// @param fmt printf-style format string
-/// @return New write position: pos + chars_written, capped at size when buffer is full.
-///         Returns size (not size-1) when full because vsnprintf already wrote the null
-///         terminator at buf[size-1]. Returning size signals "no room for more content".
-///         On encoding error, returns pos unchanged (no write occurred).
-__attribute__((format(printf, 4, 5))) static size_t buf_append(char *buf, size_t size, size_t pos, const char *fmt,
-                                                               ...) {
-  if (pos >= size) {
-    return size;
-  }
-  va_list args;
-  va_start(args, fmt);
-  int written = vsnprintf(buf + pos, size - pos, fmt, args);
-  va_end(args);
-  if (written < 0) {
-    return pos;  // encoding error
-  }
-  return std::min(pos + static_cast<size_t>(written), size);
-}
-#endif
-
 void CSE7766Component::loop() {
   const uint32_t now = App.get_loop_component_start_time();
   if (now - this->last_transmission_ >= 500) {
@@ -234,23 +207,20 @@ void CSE7766Component::parse_data_() {
 
 #if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERY_VERBOSE
   {
-    // Buffer: 7 + 15 + 33 + 15 + 25 = 95 chars max + null, rounded to 128 for safety margin.
-    // Float sizes with %.4f can be up to 11 chars for large values (e.g., 999999.9999).
-    char buf[128];
-    size_t pos = buf_append(buf, sizeof(buf), 0, "Parsed:");
+    std::string buf = "Parsed:";
     if (have_voltage) {
-      pos = buf_append(buf, sizeof(buf), pos, " V=%.4fV", voltage);
+      buf += str_sprintf(" V=%fV", voltage);
     }
     if (have_current) {
-      pos = buf_append(buf, sizeof(buf), pos, " I=%.4fmA (~%.4fmA)", current * 1000.0f, calculated_current * 1000.0f);
+      buf += str_sprintf(" I=%fmA (~%fmA)", current * 1000.0f, calculated_current * 1000.0f);
     }
     if (have_power) {
-      pos = buf_append(buf, sizeof(buf), pos, " P=%.4fW", power);
+      buf += str_sprintf(" P=%fW", power);
     }
     if (energy != 0.0f) {
-      buf_append(buf, sizeof(buf), pos, " E=%.4fkWh (%u)", energy, cf_pulses);
+      buf += str_sprintf(" E=%fkWh (%u)", energy, cf_pulses);
     }
-    ESP_LOGVV(TAG, "%s", buf);
+    ESP_LOGVV(TAG, "%s", buf.c_str());
   }
 #endif
 }

esphome/core/helpers.h

@@ -563,9 +563,11 @@ inline uint32_t fnv1_hash_object_id(const char *str, size_t len) {
 }
 
 /// snprintf-like function returning std::string of maximum length \p len (excluding null terminator).
+/// @warning Allocates heap memory. Use snprintf() with a stack buffer instead.
 std::string __attribute__((format(printf, 1, 3))) str_snprintf(const char *fmt, size_t len, ...);
 
 /// sprintf-like function returning std::string.
+/// @warning Allocates heap memory. Use snprintf() with a stack buffer instead.
 std::string __attribute__((format(printf, 1, 2))) str_sprintf(const char *fmt, ...);
 
 /// Concatenate a name with a separator and suffix using an efficient stack-based approach.

script/ci-custom.py

@@ -690,6 +690,8 @@ HEAP_ALLOCATING_HELPERS = {
     "str_truncate": "removal (function is unused)",
     "str_upper_case": "removal (function is unused)",
     "str_snake_case": "removal (function is unused)",
+    "str_sprintf": "snprintf() with a stack buffer",
+    "str_snprintf": "snprintf() with a stack buffer",
 }
 
 
@@ -706,7 +708,9 @@ HEAP_ALLOCATING_HELPERS = {
     r"get_mac_address(?!_)|"
     r"str_truncate|"
     r"str_upper_case|"
-    r"str_snake_case"
+    r"str_snake_case|"
+    r"str_sprintf|"
+    r"str_snprintf"
     r")\s*\(" + CPP_RE_EOL,
     include=cpp_include,
     exclude=[