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cpp-header-inclusion

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Enforce the strict topological header inclusion layering and reordering rules in Filament. Use this skill when adding or modifying `#include` directives in C++ source or header files.

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Source SKILL.md: https://github.com/google/filament/blob/HEAD/skills/cpp_header_inclusion/SKILL.md

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Dynamic C++ Header Inclusion & Reordering

Filament enforces a strict, acyclic include layering hierarchy to optimize compile times, prevent header pollution, and identify missing dependencies.

1. Logical Layer Hierarchy

Includes must be grouped and separated by exactly one blank line in the following order (top to bottom):

  1. Layer 0 (Corresponding Header): #include "details/Foo.h" (isolated at the very top).
  2. Layer 0.5 (Windows Cleanup): #include <utils/unwindows.h> (always second, only if needed).
  3. Layer 1 (Private/Local Headers): #include "PrivateStuff.h" (using double quotes " " strictly for private local headers located under the local target's src/ folder).
  4. Layer 2 (Internal Proprietary Libraries): Public and private includes for other internal libraries (e.g. <filaflat/...>, <backend/...>, <utils/...>, <math/...>). All proprietary library includes must use < > syntax (including private/ sub-folders). The layering priority order of these libraries is dynamically computed based on CMakeLists.txt target linkages.
  5. Layer 3 (Third-Party Libraries): <tsl/...>, <absl/...>, <jni.h>.
  6. Layer 4 (C++ Standard Library): <algorithm>, <vector>, <cstddef> (including standard <c...> wrappers).
  7. Layer 5 (POSIX System Headers): <unistd.h>, <sys/stat.h> (C system headers below C++ std, but above C std).
  8. Layer 6 (C Standard Library): Legacy C system headers ending in .h (e.g., <stdint.h>, <stddef.h>).

2. Sorting & Spacing Rules for Private Includes (Layer 1)

  • Flat-First: Flat/top-level includes (without a subdirectory prefix, e.g., "Allocators.h") are sorted above nested subdirectory includes (e.g., "components/Foo.h").
  • Visual Grouping: Private includes must be grouped by their first subdirectory path prefix, separated by exactly one blank line.

3. Running the Automated Include Formatter

AI agents must never manually sort includes or guess target dependencies. Always run the repository's dynamic topological include formatter after modifying C++ files:

./tools/reorganize-headers/run.py <file_or_directory>

Note: The tool dynamically parses CMakeLists.txt files to topologically sort proprietary libraries and includes preprocessor safety checks to avoid breaking platform-conditional include guards.