[ci] Add lint check to prevent powf in core and base entity platforms (#14126)

esphome/core/helpers.cpp

@@ -706,7 +706,7 @@ float gamma_correct(float value, float gamma) {
   if (gamma <= 0.0f)
     return value;
 
-  return powf(value, gamma);
+  return powf(value, gamma);  // NOLINT - deprecated, removal 2026.9.0
 }
 float gamma_uncorrect(float value, float gamma) {
   if (value <= 0.0f)
@@ -714,7 +714,7 @@ float gamma_uncorrect(float value, float gamma) {
   if (gamma <= 0.0f)
     return value;
 
-  return powf(value, 1 / gamma);
+  return powf(value, 1 / gamma);  // NOLINT - deprecated, removal 2026.9.0
 }
 
 void rgb_to_hsv(float red, float green, float blue, int &hue, float &saturation, float &value) {

esphome/core/helpers.h

@@ -512,8 +512,8 @@ template<size_t STACK_SIZE, typename T = uint8_t> class SmallBufferWithHeapFallb
 ///@{
 
 /// Compute 10^exp using iterative multiplication/division.
-/// Avoids pulling in powf/__ieee754_powf (~2.3KB flash) for small integer exponents.
+/// Avoids pulling in powf/__ieee754_powf (~2.3KB flash) for small integer exponents.  // NOLINT
-/// Matches powf(10, exp) for the int8_t exponent range used by sensor accuracy_decimals.
+/// Matches powf(10, exp) for the int8_t exponent range used by sensor accuracy_decimals.  // NOLINT
 inline float pow10_int(int8_t exp) {
   float result = 1.0f;
   if (exp >= 0) {

script/ci-custom.py

@@ -841,6 +841,54 @@ def lint_no_scanf(fname, match):
     )
 
 
+# Base entity platforms - these are linked into most builds and should not
+# pull in powf/__ieee754_powf (~2.3KB flash).
+BASE_ENTITY_PLATFORMS = [
+    "alarm_control_panel",
+    "binary_sensor",
+    "button",
+    "climate",
+    "cover",
+    "datetime",
+    "event",
+    "fan",
+    "light",
+    "lock",
+    "media_player",
+    "number",
+    "select",
+    "sensor",
+    "switch",
+    "text",
+    "text_sensor",
+    "update",
+    "valve",
+    "water_heater",
+]
+
+# Directories protected from powf: core + all base entity platforms
+POWF_PROTECTED_DIRS = ["esphome/core"] + [
+    f"esphome/components/{p}" for p in BASE_ENTITY_PLATFORMS
+]
+
+
+@lint_re_check(
+    r"[^\w]powf\s*\(" + CPP_RE_EOL,
+    include=[
+        f"{d}/*.{ext}" for d in POWF_PROTECTED_DIRS for ext in ["h", "cpp", "tcc"]
+    ],
+)
+def lint_no_powf_in_core(fname, match):
+    return (
+        f"{highlight('powf()')} pulls in __ieee754_powf (~2.3KB flash) and is not allowed in "
+        f"core or base entity platform code. These files are linked into every build.\n"
+        f"Please use alternatives:\n"
+        f"  - {highlight('pow10_int(exp)')} for integer powers of 10 (from helpers.h)\n"
+        f"  - Precomputed lookup tables for gamma/non-integer exponents\n"
+        f"(If powf is strictly necessary, add `// NOLINT` to the line)"
+    )
+
+
 LOG_MULTILINE_RE = re.compile(r"ESP_LOG\w+\s*\(.*?;", re.DOTALL)
 LOG_BAD_CONTINUATION_RE = re.compile(r'\\n(?:[^ \\"\r\n\t]|"\s*\n\s*"[^ \\])')
 LOG_PERCENT_S_CONTINUATION_RE = re.compile(r'\\n(?:%s|"\s*\n\s*"%s)')