ICU-22718 Export disallowed/ignored UTS 46 data for ICU4X

icu4c/source/tools/icuexportdata/icuexportdata.cpp

@@ -766,9 +766,12 @@ void computeDecompositions(const char* basename,
  std::vector<uint32_t> nonRecursive32;
  LocalUMutableCPTriePointer nonRecursiveBuilder(umutablecptrie_open(0, 0, status));
 
+ UBool uts46 = false;
+
  if (uprv_strcmp(basename, "nfkd") == 0) {
  mainNormalizer = Normalizer2::getNFKDInstance(status);
  } else if (uprv_strcmp(basename, "uts46d") == 0) {
+ uts46 = true;
  mainNormalizer = Normalizer2::getInstance(nullptr, "uts46", UNORM2_COMPOSE, status);
  } else {
  mainNormalizer = nfdNormalizer;
@@ -828,23 +831,39 @@ void computeDecompositions(const char* basename,
  nfcNormalizer->normalize(dst, nfc, status);
  nonNfdOrRoundTrips = (src == nfc);
  }
+ if (uts46) {
+ // Work around https://unicode-org.atlassian.net/browse/ICU-22658
+ // TODO: Remove the workaround after data corresponding to
+ // https://www.unicode.org/L2/L2024/24061.htm#179-C36 lands
+ // for Unicode 16.
+ switch (c) {
+ case 0x2F868:
+ dst.truncate(0);
+ dst.append(UChar32(0x36FC));
+ break;
+ case 0x2F874:
+ dst.truncate(0);
+ dst.append(UChar32(0x5F53));
+ break;
+ case 0x2F91F:
+ dst.truncate(0);
+ dst.append(UChar32(0x243AB));
+ break;
+ case 0x2F95F:
+ dst.truncate(0);
+ dst.append(UChar32(0x7AEE));
+ break;
+ case 0x2F9BF:
+ dst.truncate(0);
+ dst.append(UChar32(0x45D7));
+ break;
+ }
+ }
+
  int32_t len = dst.toUTF32(utf32, DECOMPOSITION_BUFFER_SIZE, status);
+
  if (!len || (len == 1 && utf32[0] == 0xFFFD && c != 0xFFFD)) {
- // Characters that normalize to nothing or to U+FFFD (without the
- // input being U+FFFD) in ICU4C's UTS 46 normalization normalize
- // as in NFD in ICU4X's UTF 46 normalization in the interest
- // of data size and ICU4X's normalizer being unable to handle
- // normalizing to nothing.
- // When UTS 46 is implemented on top of ICU4X, a preprocessing
- // step is supposed to remove these characters before the
- // normalization step.
- if (uprv_strcmp(basename, "uts46d") != 0) {
- status.set(U_INTERNAL_PROGRAM_ERROR);
- handleError(status, __LINE__, basename);
- }
- nfdNormalizer->normalize(src, dst, status);
- len = dst.toUTF32(utf32, DECOMPOSITION_BUFFER_SIZE, status);
- if (!len || (len == 1 && utf32[0] == 0xFFFD && c != 0xFFFD)) {
+ if (!uts46) {
  status.set(U_INTERNAL_PROGRAM_ERROR);
  handleError(status, __LINE__, basename);
  }
@@ -962,7 +981,13 @@ void computeDecompositions(const char* basename,
  if (!nonNfdOrRoundTrips) {
  compositionPassthroughBound = c;
  }
- if (len == 1 && ((utf32[0] >= 0x1161 && utf32[0] <= 0x1175) || (utf32[0] >= 0x11A8 && utf32[0] <= 0x11C2))) {
+ if (!len) {
+ if (!uts46) {
+ status.set(U_INTERNAL_PROGRAM_ERROR);
+ handleError(status, __LINE__, basename);
+ }
+ pendingTrieInsertions.push_back({c, 0xFFFFFFFF, false});
+ } else if (len == 1 && ((utf32[0] >= 0x1161 && utf32[0] <= 0x1175) || (utf32[0] >= 0x11A8 && utf32[0] <= 0x11C2))) {
  // Singleton decompositions to conjoining jamo.
  if (mainNormalizer == nfdNormalizer) {
  // Not supposed to happen in NFD