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C API: expose AAT feature and selector metadata - #525
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dfrg
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Oct 9, 2026
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Chromium probes AAT small-caps support through feat-table metadata even when HarfRust performs shaping. Add
hr_aat_layout_get_feature_typesandhr_aat_layout_feature_type_get_selector_infos, their ABI types and feature/selector constants, and a generatedhr-hb-aat.hcompatibility header. The combined header includes the AAT aliases for existing consumers.Queries use read-fonts, support callback faces, and preserve pagination/null-query conventions. Exclusive selectors disable to the global default selector; non-exclusive selectors expose enable/disable pairs and report no default index.
Stacked on #524. Completes the 12 uncovered Chromium metadata functions listed in #520 together with #521, #523, and #524; Chromium build/behavioral integration work remains.
Validation: 146 C API tests; 116,180 metadata comparisons against HarfBuzz 14.5.1 across 500 faces, including synthetic exclusive/non-exclusive AAT features; Clippy 1.99; Rust 1.85 checking; GCC/Clang C99 linking and C++17 header checks, including selector struct layout.
The Chromium build experiment additionally exposed signed integer macros in Blink's unsigned feature-vector comparisons. The generated AAT constants now retain unsigned literal types, with a C++11 CI regression check. The updated 146 C API tests, Clippy, and C++ check pass locally.