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@Jason2866 Jason2866 commented Nov 14, 2025

Description:

To enable LTO for the Arduino HybridCompile part add in platformio.ini in the env:

build_unflags = -fno-lto

Do not set anything regarding LTO in build_flags this would enable LTO for the espidf HybridCompile part of the Arduino Libs! The espidf framework does not compile successfully with enabled LTO

@mathieucarbou fyi

Checklist:

  • The pull request is done against the latest develop branch
  • Only relevant files were touched
  • Only one feature/fix was added per PR, more changes are allowed when changing boards.json
  • I accept the CLA

Summary by CodeRabbit

  • New Features
    • Introduced Link Time Optimization (LTO) support for HybridCompile Arduino projects. The build system now automatically detects and manages LTO configuration, enabling projects to leverage advanced optimization techniques when enabled in build settings.

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coderabbitai bot commented Nov 14, 2025

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Walkthrough

The changes implement Link-Time Optimization (LTO) flag management for HybridCompile Arduino builds. When -fno-lto is detected in build unflags, the system enables LTO by removing no-LTO flags and applying LTO flags to the Arduino build script through two new component manager methods.

Changes

Cohort / File(s) Summary
LTO detection and invocation
builder/frameworks/arduino.py
Introduces global flag_lto flag. Detects -fno-lto in BUILD_UNFLAGS and conditionally invokes component manager methods to remove and add LTO flags at two lifecycle points.
LTO flag manipulation
builder/frameworks/component_manager.py
Adds remove_no_lto_flags() method to strip -fno-lto from pioarduino-build.py with syntax sanitization. Adds add_lto_flags() method to inject -flto into CCFLAGS, CFLAGS, CXXFLAGS, and LINKFLAGS in the same file. Both include existence checks and error handling.

Sequence Diagram

sequenceDiagram
    participant Arduino as arduino.py
    participant CompMgr as ComponentManager
    participant BuildScript as pioarduino-build.py

    Arduino->>Arduino: Detect -fno-lto in BUILD_UNFLAGS
    Arduino->>Arduino: Set flag_lto = True
    
    rect rgb(240, 248, 255)
    note right of Arduino: Lifecycle Point 1 & 2
    Arduino->>CompMgr: remove_no_lto_flags()
    CompMgr->>BuildScript: Read file
    CompMgr->>BuildScript: Remove all -fno-lto occurrences
    CompMgr->>BuildScript: Sanitize syntax (commas/brackets)
    CompMgr->>BuildScript: Write back
    CompMgr-->>Arduino: Return True/False
    end
    
    rect rgb(240, 255, 240)
    Arduino->>CompMgr: add_lto_flags()
    CompMgr->>BuildScript: Read file
    CompMgr->>BuildScript: Insert -flto into CCFLAGS, CFLAGS, CXXFLAGS, LINKFLAGS
    CompMgr->>BuildScript: Write back if modified
    CompMgr->>CompMgr: Print notification
    CompMgr-->>Arduino: Return True/False
    end
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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Areas requiring attention:

  • Text manipulation logic in remove_no_lto_flags() and add_lto_flags() for correctness of flag insertion/removal patterns
  • Syntax sanitization approach (comma/bracket handling) in removal method
  • Error handling and edge cases when build script file is missing or unwritable
  • Integration points in arduino.py where component manager methods are invoked (lifecycle correctness)

Poem

🐰 Flags flutter like carrots in the wind,
No-LTO banished, LTO pinned!
The ComponentManager hops with glee,
Optimizing Arduino builds, wild and free!

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)
Check name Status Explanation
Title check ✅ Passed The title clearly and specifically describes the main change: adding an option to enable LTO (Link Time Optimization) for the Arduino part of HybridCompile, which directly aligns with the changeset's core functionality of detecting -fno-lto flags and enabling LTO management.
Docstring Coverage ✅ Passed Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.

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@Jason2866
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@coderabbitai full review

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coderabbitai bot commented Nov 14, 2025

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Actionable comments posted: 3

🧹 Nitpick comments (2)
builder/frameworks/component_manager.py (1)

1275-1310: Consider using the logger and adding validation.

The method bypasses the class's logger instance and prints directly to stdout, which is inconsistent with other methods in ComponentManager (e.g., _cleanup_removed_components, _batch_remove_cpppath_entries). Additionally, no validation is performed on the modified content before writing it back.

Consider these improvements:

     def remove_no_lto_flags(self) -> bool:
         """
         Remove all -fno-lto flags from pioarduino-build.py.
 
         Removes all occurrences of -fno-lto from CCFLAGS, CFLAGS, CXXFLAGS,
         and LINKFLAGS in the Arduino build script.
 
         Returns:
             bool: True if successful, False otherwise
         """
         build_py_path = str(Path(self.config.arduino_libs_mcu) / "pioarduino-build.py")
 
         if not os.path.exists(build_py_path):
-            print(f"Warning: pioarduino-build.py not found at {build_py_path}")
+            self.logger.log_change(f"Warning: pioarduino-build.py not found at {build_py_path}")
             return False
 
         try:
             with open(build_py_path, 'r', encoding='utf-8') as f:
                 content = f.read()
 
             # Remove all -fno-lto flags
             modified_content = re.sub(r'["\']?-fno-lto["\']?,?\s*', '', content)
 
             # Clean up any resulting empty strings or double commas
             modified_content = re.sub(r',\s*,', ',', modified_content)
             modified_content = re.sub(r'\[\s*,', '[', modified_content)
             modified_content = re.sub(r',\s*\]', ']', modified_content)
 
+            # Basic validation
+            if not modified_content or len(modified_content) < len(content) * 0.5:
+                self.logger.log_change("Warning: Modified content looks suspicious, aborting")
+                return False
+
             with open(build_py_path, 'w', encoding='utf-8') as f:
                 f.write(modified_content)
 
+            self.logger.log_change("Removed -fno-lto flags from build script")
             return True
 
         except (IOError, OSError) as e:
-            print(f"Error removing -fno-lto flags: {e}")
+            self.logger.log_change(f"Error removing -fno-lto flags: {e}")
             return False
builder/frameworks/arduino.py (1)

602-603: Consider adding a comment to clarify the counterintuitive logic.

The logic where -fno-lto in build_unflags enables LTO is counterintuitive. A brief comment would help future maintainers understand this design choice.

+    # Check if user wants to enable LTO for Arduino part by unflagging -fno-lto
     if '-fno-lto' in build_unflags:
         flag_lto = True
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📥 Commits

Reviewing files that changed from the base of the PR and between 23c0c5b and 59150e7.

📒 Files selected for processing (2)
  • builder/frameworks/arduino.py (3 hunks)
  • builder/frameworks/component_manager.py (1 hunks)
🧰 Additional context used
🧠 Learnings (1)
📓 Common learnings
Learnt from: Jason2866
Repo: pioarduino/platform-espressif32 PR: 0
File: :0-0
Timestamp: 2025-09-23T12:35:35.508Z
Learning: For the pioarduino/platform-espressif32 project, Jason2866 has explicitly instructed to NEVER create issues or PRs outside of his repositories (pioarduino/*). All issue and PR creation must be strictly limited to his own repositories only, never in upstream or other repositories.
Learnt from: Jason2866
Repo: pioarduino/platform-espressif32 PR: 0
File: :0-0
Timestamp: 2025-09-23T12:35:35.508Z
Learning: For the pioarduino/platform-espressif32 project, Jason2866 has explicitly instructed to NEVER create issues or PRs outside of his repositories (pioarduino/*). All issue and PR creation must be strictly limited to his own repositories only, never in upstream or other repositories.
Learnt from: Jason2866
Repo: pioarduino/platform-espressif32 PR: 281
File: builder/frameworks/component_manager.py:1047-1054
Timestamp: 2025-09-04T15:27:18.112Z
Learning: In the pioarduino/platform-espressif32 project, Jason2866 prefers not to add guard checks for missing arduino_libs_mcu in backup operations, preferring to let the operation proceed rather than silently skip when the directory might be missing.
Learnt from: Jason2866
Repo: pioarduino/platform-espressif32 PR: 268
File: builder/penv_setup.py:87-96
Timestamp: 2025-08-26T14:52:29.044Z
Learning: For the pioarduino/platform-espressif32 project, Jason2866 prefers to trust system executables when falling back to PATH-based command resolution (like "uv"), rather than implementing additional validation checks for security concerns.
🪛 Ruff (0.14.4)
builder/frameworks/component_manager.py

1306-1306: Consider moving this statement to an else block

(TRY300)


1332-1332: Local variable original_content is assigned to but never used

Remove assignment to unused variable original_content

(F841)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (7)
  • GitHub Check: build (macos-15, examples/espidf-peripherals-usb)
  • GitHub Check: build (macos-15, examples/espidf-coap-server)
  • GitHub Check: build (macos-15, examples/espidf-blink)
  • GitHub Check: build (macos-15, examples/tasmota)
  • GitHub Check: build (macos-15, examples/espidf-arduino-blink)
  • GitHub Check: build (windows-latest, examples/arduino-wifiscan)
  • GitHub Check: build (windows-latest, examples/arduino-blink)
🔇 Additional comments (1)
builder/frameworks/arduino.py (1)

535-535: LGTM! Clean initialization of the LTO flag.

The flag initialization is consistent with other flag patterns in the file.

@mathieucarbou
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@Jason2866 : so to summarize, LTO becomes activated when LTO flag is removed ? 😆

@Jason2866
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Jason2866 commented Nov 14, 2025

@mathieucarbou LTO gets activated since the -fno_lto is removed the no stands for no LTO
So it gets activated since the forbid flag for LTO is removed. Luckily this has no impact for IDF. LTO is still off, since it needs explicit enabling. By doing this way a very intrusive code part in espidf.py can be avoided.

@Jason2866 Jason2866 merged commit 08a860e into develop Nov 14, 2025
68 checks passed
@Jason2866 Jason2866 deleted the hybrid_lto branch November 15, 2025 14:11
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3 participants