capi: collect nominal cmap Unicode coverage

harfrust_capi/README.md

@@ -134,6 +134,7 @@ callback with `hr_face_create_for_tables`, which asks for one table at a time.
 Use `hr_face_set_get_table_tags_func` to enumerate the tables of a callback
 face; blob faces enumerate their SFNT directory automatically.
 `hr_face_set_index` changes the reported index without selecting new tables.
+`hr_face_collect_unicodes` adds the selected cmap subtable's coverage to a set.
 
 `hr_shape` already reuses shape plans through a per-face cache, the way
 `hb_shape` does internally, so reach for `hr_shape_plan_create` only when you

harfrust_capi/include/hr-hb.h

@@ -120,6 +120,7 @@
 #define hb_direction_from_string                         hr_direction_from_string
 #define hb_direction_t                                   hr_direction_t
 #define hb_direction_to_string                           hr_direction_to_string
+#define hb_face_collect_unicodes                         hr_face_collect_unicodes
 #define hb_face_count                                    hr_face_count
 #define hb_face_create                                   hr_face_create
 #define hb_face_create_for_tables                        hr_face_create_for_tables

harfrust_capi/include/hr.h

@@ -3704,6 +3704,18 @@ struct hr_blob_t *hr_face_reference_blob(struct hr_face_t *face);
  */
 struct hr_blob_t *hr_face_reference_table(struct hr_face_t *face, hr_tag_t tag);
 
+/**
+ * Adds the face's nominal cmap coverage to `out`, preserving existing entries.
+ *
+ * Uses the selected cmap subtable's stored character codes, without the symbol
+ * fallback or Mac Roman conversion applied by nominal glyph lookup. Variation
+ * sequences are not included. A missing cmap adds nothing.
+ * # Safety
+ * `face` must be null or live; `out` must be null or live and must not be
+ * accessed concurrently while it is being modified.
+ */
+void hr_face_collect_unicodes(struct hr_face_t *face, struct hr_set_t *out);
+
 /**
  * Creates a font over a face.
  *

harfrust_capi/src/face.rs

@@ -6,12 +6,17 @@ use std::sync::{Arc, OnceLock};
 
 use harfrust::font::{Blob, Font, TableFunction};
 use harfrust::Tag;
-use read_fonts::{model::Format, TableProvider};
+use read_fonts::{
+    model::Format,
+    tables::cmap::{CmapIterLimits, CmapSubtable},
+    TableProvider,
+};
 
 use crate::blob::hr_blob_t;
 use crate::common::{hr_bool_t, hr_tag_t, tag_from_rust, tag_to_rust};
 use crate::object::{self, hr_destroy_func_t, hr_user_data_key_t, Empty, Object, ObjectHeader};
 use crate::plan::PlanCache;
+use crate::set::hr_set_t;
 
 /// Callback returning the data for one table of a face.
 ///
@@ -565,3 +570,54 @@ pub unsafe extern "C" fn hr_face_reference_table(
         }
     }
 }
+
+/// Adds the face's nominal cmap coverage to `out`, preserving existing entries.
+///
+/// Uses the selected cmap subtable's stored character codes, without the symbol
+/// fallback or Mac Roman conversion applied by nominal glyph lookup. Variation
+/// sequences are not included. A missing cmap adds nothing.
+/// # Safety
+/// `face` must be null or live; `out` must be null or live and must not be
+/// accessed concurrently while it is being modified.
+#[no_mangle]
+pub unsafe extern "C" fn hr_face_collect_unicodes(face: *mut hr_face_t, out: *mut hr_set_t) {
+    let face = unsafe { object::or_empty(face.cast_const()) };
+    let Some(font) = face.font() else { return };
+    let Some((_, _, subtable)) = font
+        .tables()
+        .cmap()
+        .ok()
+        .and_then(|table| table.best_subtable())
+    else {
+        return;
+    };
+    let Some(out) = (unsafe { object::as_mutable(out) }) else {
+        return;
+    };
+    // A format 13 group maps an entire range to one glyph. Insert ranges
+    // directly, both to bound malformed glyph IDs and to avoid iterating
+    // over a million characters in a last-resort font.
+    if let CmapSubtable::Format13(table) = subtable {
+        for group in table.groups() {
+            let first = group.start_char_code();
+            let last = group.end_char_code().min(0x0010_FFFF);
+            let glyph = group.glyph_id();
+            if first <= last && glyph != 0 && glyph < font.num_glyphs() {
+                out.values.insert_range(first..=last);
+            }
+        }
+    } else {
+        let limits = CmapIterLimits {
+            // The iterator's character limit is exclusive.
+            max_char: 0x0011_0000,
+            glyph_count: font.num_glyphs(),
+        };
+        let is_format4 = matches!(subtable, CmapSubtable::Format4(_));
+        for (codepoint, glyph) in subtable.iter_with_limits(limits) {
+            // Format 4's final U+FFFF segment is a sentinel.
+            if glyph.to_u32() != 0 && !(is_format4 && codepoint == 0xFFFF) {
+                out.add(codepoint);
+            }
+        }
+    }
+}

harfrust_capi/tests/skia_face.rs

@@ -155,3 +155,53 @@ fn default_unicode_scripts_match_itemization_needs() {
         assert_eq!(hr_unicode_script(ptr::null_mut(), codepoint), script);
     }
 }
+
+#[test]
+fn unicode_collection_adds_coverage_without_clearing_the_set() {
+    unsafe {
+        let face = face();
+        let set = hr_set_create();
+        hr_set_add(set, 0x0010_FFFF);
+        hr_face_collect_unicodes(face, set);
+        for codepoint in ['A', 'a', 'b'] {
+            assert_eq!(hr_set_has(set, codepoint as u32), 1);
+        }
+        assert_eq!(hr_set_has(set, 0x0010_FFFF), 1);
+        let population = hr_set_get_population(set);
+        assert!(population > 3);
+        hr_face_collect_unicodes(face, set);
+        hr_face_collect_unicodes(ptr::null_mut(), set);
+        hr_face_collect_unicodes(face, ptr::null_mut());
+        hr_face_collect_unicodes(face, hr_set_get_empty());
+        assert_eq!(hr_set_get_population(set), population);
+        hr_set_invert(set);
+        hr_set_del(set, 'a' as u32);
+        hr_face_collect_unicodes(face, set);
+        assert_eq!(hr_set_has(set, 'a' as u32), 1);
+        hr_set_destroy(set);
+        hr_face_destroy(face);
+    }
+}
+
+#[test]
+fn unicode_collection_covers_constant_format13_ranges() {
+    unsafe {
+        let data = include_bytes!("../../harfrust/tests/fonts/in-house/AdobeBlank2.ttf");
+        let blob = hr_blob_create(
+            data.as_ptr().cast(),
+            data.len() as u32,
+            HR_MEMORY_MODE_READONLY,
+            ptr::null_mut(),
+            None,
+        );
+        let face = hr_face_create(blob, 0);
+        hr_blob_destroy(blob);
+        let set = hr_set_create();
+        hr_face_collect_unicodes(face, set);
+        assert_eq!(hr_set_get_population(set), 1_111_998);
+        assert_eq!(hr_set_has(set, 0), 1);
+        assert_eq!(hr_set_has(set, 0x0010_FFFD), 1);
+        hr_set_destroy(set);
+        hr_face_destroy(face);
+    }
+}

scripts/test-capi-coverage.py

@@ -0,0 +1,124 @@
+#!/usr/bin/env python3
+"""Compare nominal cmap coverage with HarfBuzz.
+
+Build harfrust_capi, then run:
+  python3 scripts/test-capi-coverage.py --library /path/to/libharfrust_c.so \
+      --harfbuzz /path/to/libharfbuzz.so --fonts harfrust/tests/fonts
+
+HarfBuzz 14.5.1 incorrectly truncates format-13 constant-glyph ranges as though
+glyph IDs incremented within each range. For those subtables, independently
+check HarfRust's complete ranges and report the HarfBuzz difference separately.
+"""
+import argparse
+import ctypes as C
+from pathlib import Path
+import struct
+
+U, P = C.c_uint, C.c_void_p
+SEED = 0x10FFFF
+
+
+class Api:
+    def __init__(self, library, prefix):
+        self.library = C.CDLL(library)
+
+        def bind(name, result, arguments):
+            function = getattr(self.library, prefix + name)
+            function.restype = result
+            function.argtypes = arguments
+            return function
+
+        self.blob = bind("blob_create", P, [P, U, C.c_int, P, P])
+        self.drop_blob = bind("blob_destroy", None, [P])
+        self.blob_data = bind("blob_get_data", P, [P, C.POINTER(U)])
+        self.face = bind("face_create", P, [P, U])
+        self.face_count = bind("face_count", U, [P])
+        self.drop_face = bind("face_destroy", None, [P])
+        self.table = bind("face_reference_table", P, [P, U])
+        self.glyph_count = bind("face_get_glyph_count", U, [P])
+        self.make_set = bind("set_create", P, [])
+        self.drop_set = bind("set_destroy", None, [P])
+        self.add = bind("set_add", None, [P, U])
+        self.collect = bind("face_collect_unicodes", None, [P, P])
+        self.next = bind("set_next", C.c_int, [P, C.POINTER(U)])
+
+    def coverage(self, face):
+        output = self.make_set()
+        self.add(output, SEED)
+        self.collect(face, output)
+        value, values = U(0xFFFFFFFF), set()
+        while self.next(output, C.byref(value)):
+            values.add(value.value)
+        self.drop_set(output)
+        return values
+
+    def format13_coverage(self, face):
+        blob = self.table(face, int.from_bytes(b"cmap", "big"))
+        size = U()
+        pointer = self.blob_data(blob, C.byref(size))
+        data = C.string_at(pointer, size.value) if size.value else b""
+        self.drop_blob(blob)
+        if len(data) < 4:
+            return None
+        count = struct.unpack_from(">H", data, 2)[0]
+        records = [struct.unpack_from(">HHI", data, 4 + i * 8) for i in range(count)]
+        priority = [(3, 0), (3, 10), (0, 6), (0, 4), (3, 1),
+                    (0, 3), (0, 2), (0, 1), (0, 0), (1, 0)]
+        for platform, encoding in priority:
+            for record_platform, record_encoding, offset in records:
+                if (platform, encoding) != (record_platform, record_encoding):
+                    continue
+                format_id = struct.unpack_from(">H", data, offset)[0]
+                if format_id not in (0, 4, 6, 10, 12, 13):
+                    continue
+                if format_id != 13:
+                    return None
+                groups = struct.unpack_from(">I", data, offset + 12)[0]
+                glyph_count = self.glyph_count(face)
+                result = {SEED}
+                for i in range(groups):
+                    first, last, glyph = struct.unpack_from(">III", data, offset + 16 + i * 12)
+                    if 0 < glyph < glyph_count:
+                        result.update(range(first, min(last, 0x10FFFF) + 1))
+                return result
+        return None
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--library", required=True)
+    parser.add_argument("--harfbuzz", required=True)
+    parser.add_argument("--fonts", type=Path, required=True)
+    args = parser.parse_args()
+    hr, hb = Api(args.library, "hr_"), Api(args.harfbuzz, "hb_")
+    matched, corrected = 0, 0
+    for path in sorted(args.fonts.rglob("*")):
+        if path.suffix.lower() not in {".ttf", ".otf", ".ttc"}:
+            continue
+        data = path.read_bytes()
+        hr_blob = hr.blob(data, len(data), 0, None, None)
+        hb_blob = hb.blob(data, len(data), 0, None, None)
+        for index in range(hb.face_count(hb_blob)):
+            hr_face, hb_face = hr.face(hr_blob, index), hb.face(hb_blob, index)
+            try:
+                actual, expected = hr.coverage(hr_face), hb.coverage(hb_face)
+                if actual == expected:
+                    matched += 1
+                else:
+                    complete = hr.format13_coverage(hr_face)
+                    assert complete is not None and actual == complete and expected <= actual, (
+                        path, index, len(actual), len(expected), sorted(actual ^ expected)[:10])
+                    print(f"Complete format-13 coverage: {path} face {index}; "
+                          f"HarfRust {len(actual)} entries, HarfBuzz {len(expected)}")
+                    corrected += 1
+            finally:
+                hr.drop_face(hr_face)
+                hb.drop_face(hb_face)
+        hr.drop_blob(hr_blob)
+        hb.drop_blob(hb_blob)
+    print(f"Matched {matched} coverage sets; independently checked {corrected} "
+          "complete format-13 coverage sets (counts include a seeded existing entry).")
+
+
+if __name__ == "__main__":
+    main()