[clang] [APINotes] Support fields of C/C++ structs (PR #104088)

[Saleem Abdulrasool via cfe-commits]

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@@ -858,6 +867,62 @@ void APINotesWriter::Implementation::writeCXXMethodBlock(
   }
 }
 
+namespace {
+/// Used to serialize the on-disk C field table.
+class FieldTableInfo
+    : public VersionedTableInfo<FieldTableInfo, SingleDeclTableKey, FieldInfo> {
+public:
+  unsigned getKeyLength(key_type_ref) {
+    return sizeof(uint32_t) + sizeof(uint32_t);
+  }
+
+  void EmitKey(raw_ostream &OS, key_type_ref Key, unsigned) {
+    llvm::support::endian::Writer writer(OS, llvm::endianness::little);
+    writer.write<uint32_t>(Key.parentContextID);
+    writer.write<uint32_t>(Key.nameID);
+  }
+
+  hash_value_type ComputeHash(key_type_ref key) {
+    return static_cast<size_t>(key.hashValue());
+  }
+
+  unsigned getUnversionedInfoSize(const FieldInfo &FI) {
+    return getVariableInfoSize(FI);
+  }
+
+  void emitUnversionedInfo(raw_ostream &OS, const FieldInfo &FI) {
+    emitVariableInfo(OS, FI);
+  }
+};
+} // namespace
+
+void APINotesWriter::Implementation::writeFieldBlock(
+    llvm::BitstreamWriter &Stream) {
+  llvm::BCBlockRAII Scope(Stream, FIELD_BLOCK_ID, 3);
+
+  if (Fields.empty())
+    return;
+
+  {
+    llvm::SmallString<4096> HashTableBlob;
+    uint32_t Offset;
+    {
+      llvm::OnDiskChainedHashTableGenerator<FieldTableInfo> Generator;
+      for (auto &MD : Fields)
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compnerd wrote:

`FD` would be a better initialism

https://github.com/llvm/llvm-project/pull/104088