Merge branch 'deprecate_get_icon_get_device_class_get_unit_of_measurement' into integration

deprecate_get_icon_get_device_class_get_unit_of_measurement_pr.md

@@ -0,0 +1,125 @@
+# PR Title Suggestion
+
+```
+[core] Deprecate get_icon(), get_device_class(), get_unit_of_measurement() and fix remaining non-MQTT usages
+```
+
+# What does this implement/fix?
+
+This PR deprecates three inefficient methods in `entity_base.h` that return `std::string` copies and updates the remaining non-MQTT usages in the core codebase to use the more efficient `StringRef` alternatives.
+
+## Background
+
+PR #11731 eliminates MQTT component usages of these methods, demonstrating significant performance improvements by avoiding unnecessary string copies. This PR completes the migration by:
+
+1. Adding deprecation warnings to the old methods
+2. Fixing the remaining non-MQTT usages in prometheus, graph, and sprinkler components
+3. Setting a clear removal timeline (ESPHome 2026.5.0)
+
+**Note:** This PR should be merged **after** PR #11731 is merged to ensure all internal usages are updated before deprecation warnings are enabled.
+
+## Changes
+
+### 1. Deprecate inefficient methods (entity_base.h)
+
+Added `[[deprecated]]` attributes to:
+- `EntityBase::get_icon()` → Use `get_icon_ref()` instead
+- `EntityBase_DeviceClass::get_device_class()` → Use `get_device_class_ref()` instead
+- `EntityBase_UnitOfMeasurement::get_unit_of_measurement()` → Use `get_unit_of_measurement_ref()` instead
+
+**Deprecation message:** "Use <method>_ref() instead for better performance (avoids string copy). Will stop working in ESPHome 2026.5.0"
+
+### 2. Fix remaining components (prometheus, graph, sprinkler)
+
+Updated 3 components to use `get_unit_of_measurement_ref()` instead of `get_unit_of_measurement()`:
+
+- **prometheus_handler.cpp** (line 161): Eliminates temporary string allocation when printing metrics
+- **graph.cpp** (lines 238, 374): Direct `StringRef` appending to `std::string` (uses `StringRef` operator `+=` overload)
+- **sprinkler.cpp** (lines 653, 735): Zero-allocation string comparisons with `MIN_STR`
+
+## Why deprecate instead of remove immediately?
+
+This is a **breaking change** for external components, but we're using a gradual deprecation approach:
+
+1. **External components:** Many third-party components may use these methods - immediate removal would break them without notice
+2. **Migration path:** Gives external component authors 6 months to update with clear compiler warnings
+3. **Clear timeline:** ESPHome 2026.5.0 gives a concrete removal date that can be communicated in release notes
+4. **Compiler warnings:** External components will see deprecation warnings during compilation, making the migration explicit and traceable
+5. **Simple migration:** The fix is straightforward - replace `get_X()` with `get_X_ref()` (add `.c_str()` if passing to functions expecting `const char*`)
+
+## Benefits
+
+### Performance improvements:
+- **Eliminates string copies** in hot code paths (prometheus metrics, graph rendering, sprinkler logic)
+- **Reduces heap fragmentation** on ESP8266 where memory is constrained
+- **Faster string comparisons** (sprinkler component)
+- **Safer code** (prometheus: no more `.c_str()` on temporaries)
+
+### Code quality improvements:
+- **Consistent API usage:** All core code now uses `*_ref()` methods
+- **Better practices:** Encourages zero-copy string handling
+- **Clear migration path:** External components have time and guidance to update
+
+### Flash/RAM impact:
+- Minimal: Deprecation attributes add no runtime overhead
+- Once methods are removed in 2026.5.0: ~200-500 bytes flash savings (removes unused vtable entries and std::string conversions)
+
+## Timeline
+
+1. **Today:** Merge this PR (deprecates methods, fixes core usage)
+   - Deprecation warnings appear during compilation for external components
+   - All core components updated to use `*_ref()` methods
+2. **Next 6 months:** External components see deprecation warnings, maintainers update their code
+   - Component authors have time to migrate to `*_ref()` methods
+   - Warnings provide clear guidance on what to change
+3. **ESPHome 2026.5.0:** **BREAKING CHANGE** - Remove the three deprecated methods entirely
+   - External components still using old methods will fail to compile
+   - Migration is simple: replace `get_X()` with `get_X_ref()` (or `.c_str()` if needed)
+
+## Dependencies
+
+**This PR depends on PR #11731 being merged first.**
+
+PR #11731 eliminates MQTT component usages (8 components × 2 calls = 16 string copies per discovery cycle). Once that's merged, this PR:
+1. Adds deprecation warnings to guide external components
+2. Fixes the remaining 3 components (prometheus, graph, sprinkler)
+3. Completes the migration for all core components
+
+## Merge Order
+
+1. **First:** Merge PR #11731 (fixes MQTT components)
+2. **Then:** Merge this PR (adds deprecation warnings + fixes remaining components)
+
+## Types of changes
+
+- [x] Code quality improvements to existing code
+- [x] Deprecation of inefficient APIs
+- [x] **Breaking change** (External components using these methods will break in ESPHome 2026.5.0)
+
+## Test Environment
+
+- [ ] ESP32 IDF
+- [ ] ESP32 Arduino
+- [ ] ESP8266 Arduino
+- [ ] RP2040
+
+## Example entry for `config.yaml`:
+
+No configuration changes required. This is a transparent optimization for all components.
+
+External component authors using the deprecated methods will see compiler warnings:
+
+```
+warning: 'get_unit_of_measurement' is deprecated: Use get_unit_of_measurement_ref() instead
+for better performance (avoids string copy). Will stop working in ESPHome 2026.5.0
+[-Wdeprecated-declarations]
+```
+
+## Checklist:
+  - [ ] The code change is tested and works locally.
+  - [ ] Tests have been added to verify that the new code works (under `tests/` folder).
+    - Existing component tests cover the updated code paths
+
+If user exposed functionality or configuration variables are added/changed:
+  - [ ] Documentation added/updated in [esphome-docs](https://github.com/esphome/esphome-docs).
+    - N/A - PR summary will be automatically added to release notes

esphome/components/graph/graph.cpp

@@ -235,7 +235,7 @@ void GraphLegend::init(Graph *g) {
       std::string valstr =
           value_accuracy_to_string(trace->sensor_->get_state(), trace->sensor_->get_accuracy_decimals());
       if (this->units_) {
-        valstr += trace->sensor_->get_unit_of_measurement_ref().c_str();
+        valstr += trace->sensor_->get_unit_of_measurement_ref();
       }
       this->font_value_->measure(valstr.c_str(), &fw, &fos, &fbl, &fh);
       if (fw > valw)
@@ -371,7 +371,7 @@ void Graph::draw_legend(display::Display *buff, uint16_t x_offset, uint16_t y_of
       std::string valstr =
           value_accuracy_to_string(trace->sensor_->get_state(), trace->sensor_->get_accuracy_decimals());
       if (legend_->units_) {
-        valstr += trace->sensor_->get_unit_of_measurement_ref().c_str();
+        valstr += trace->sensor_->get_unit_of_measurement_ref();
       }
       buff->printf(xv, yv, legend_->font_value_, trace->get_line_color(), TextAlign::TOP_CENTER, "%s", valstr.c_str());
       ESP_LOGV(TAG, "    value: %s", valstr.c_str());