feat(xlang): add decimal and align serializers for xlang (#3599)

## Why?



## What does this PR do?



## Related issues



## AI Contribution Checklist



- [ ] Substantial AI assistance was used in this PR: `yes` / `no`
- [ ] If `yes`, I included a completed [AI Contribution
Checklist](https://github.com/apache/fory/blob/main/AI_POLICY.md#9-contributor-checklist-for-ai-assisted-prs)
in this PR description and the required `AI Usage Disclosure`.
- [ ] If `yes`, my PR description includes the required `ai_review`
summary and screenshot evidence of the final clean AI review results
from both fresh reviewers on the current PR diff or current HEAD after
the latest code changes.



## Does this PR introduce any user-facing change?



- [ ] Does this PR introduce any public API change?
- [ ] Does this PR introduce any binary protocol compatibility change?

## Benchmark

Author: chaokunyang

compiler/fory_compiler/generators/cpp.py

@@ -66,6 +66,7 @@ class CppGenerator(BaseGenerator):
         PrimitiveKind.FLOAT64: "double",
         PrimitiveKind.STRING: "std::string",
         PrimitiveKind.BYTES: "std::vector<uint8_t>",
+        PrimitiveKind.DECIMAL: "fory::serialization::Decimal",
         PrimitiveKind.DATE: "fory::serialization::Date",
         PrimitiveKind.TIMESTAMP: "fory::serialization::Timestamp",
         PrimitiveKind.ANY: "std::any",
@@ -1779,6 +1780,8 @@ def collect_includes(
                 includes.add("<string>")
             elif field_type.kind == PrimitiveKind.BYTES:
                 includes.add("<vector>")
+            elif field_type.kind == PrimitiveKind.DECIMAL:
+                includes.add('"fory/serialization/decimal_serializers.h"')
             elif field_type.kind in (PrimitiveKind.DATE, PrimitiveKind.TIMESTAMP):
                 includes.add('"fory/serialization/temporal_serializers.h"')
             elif field_type.kind == PrimitiveKind.ANY:

compiler/fory_compiler/generators/dart.py

@@ -67,6 +67,7 @@ class DartGenerator(BaseGenerator):
         PrimitiveKind.BYTES: "Uint8List",
         PrimitiveKind.DATE: "LocalDate",
         PrimitiveKind.TIMESTAMP: "Timestamp",
+        PrimitiveKind.DECIMAL: "Decimal",
         PrimitiveKind.ANY: "Object?",
     }
 
@@ -610,6 +611,7 @@ def _default_value_for_type(
                 PrimitiveKind.BYTES: "Uint8List(0)",
                 PrimitiveKind.DATE: "const LocalDate(1970, 1, 1)",
                 PrimitiveKind.TIMESTAMP: "Timestamp(0, 0)",
+                PrimitiveKind.DECIMAL: "const Decimal.zero()",
                 PrimitiveKind.ANY: "null",
             }[t.kind]
         if isinstance(t, ListType):

compiler/fory_compiler/generators/go.py

@@ -197,6 +197,7 @@ def message_has_unions(self, message: Message) -> bool:
         PrimitiveKind.BYTES: "[]byte",
         PrimitiveKind.DATE: "fory.Date",
         PrimitiveKind.TIMESTAMP: "time.Time",
+        PrimitiveKind.DECIMAL: "fory.Decimal",
         PrimitiveKind.ANY: "any",
     }
 
@@ -666,6 +667,7 @@ def get_union_case_type_id_expr(
                 PrimitiveKind.BYTES: "fory.BINARY",
                 PrimitiveKind.DATE: "fory.DATE",
                 PrimitiveKind.TIMESTAMP: "fory.TIMESTAMP",
+                PrimitiveKind.DECIMAL: "fory.DECIMAL",
                 PrimitiveKind.ANY: "fory.UNKNOWN",
             }
             return primitive_type_ids.get(kind, "fory.UNKNOWN")

compiler/fory_compiler/generators/javascript.py

@@ -147,7 +147,7 @@ class JavaScriptGenerator(BaseGenerator):
         PrimitiveKind.DATE: "Date",
         PrimitiveKind.TIMESTAMP: "Date",
         PrimitiveKind.DURATION: "number",
-        # DECIMAL is not supported by the JS runtime; rejected in _field_type_expr.
+        PrimitiveKind.DECIMAL: "Decimal",
         PrimitiveKind.ANY: "any",
     }
 
@@ -177,7 +177,7 @@ class JavaScriptGenerator(BaseGenerator):
         PrimitiveKind.DATE: "Type.date()",
         PrimitiveKind.TIMESTAMP: "Type.timestamp()",
         PrimitiveKind.DURATION: "Type.duration()",
-        # DECIMAL is not yet supported by the JS runtime; omitted intentionally.
+        PrimitiveKind.DECIMAL: "Type.decimal()",
         PrimitiveKind.ANY: "Type.any()",
     }
 
@@ -531,6 +531,9 @@ def generate_imports(self) -> List[str]:
         lines: List[str] = []
         imported_regs = self._collect_imported_registrations()
 
+        if self._schema_uses_primitive_kind(PrimitiveKind.DECIMAL):
+            lines.append("import { Decimal } from '@apache-fory/core';")
+
         # Collect all imported types used in this schema
         imported_types_by_module: Dict[str, Set[str]] = {}
 
@@ -577,6 +580,39 @@ def generate_imports(self) -> List[str]:
 
         return lines
 
+    def _schema_uses_primitive_kind(self, primitive_kind: PrimitiveKind) -> bool:
+        def uses_field_type(field_type: FieldType) -> bool:
+            if isinstance(field_type, PrimitiveType):
+                return field_type.kind == primitive_kind
+            if isinstance(field_type, NamedType):
+                return field_type.name.lower() == primitive_kind.value
+            if isinstance(field_type, ListType):
+                return uses_field_type(field_type.element_type)
+            if isinstance(field_type, MapType):
+                return uses_field_type(field_type.key_type) or uses_field_type(
+                    field_type.value_type
+                )
+            return False
+
+        def uses_message(message: Message) -> bool:
+            for field in message.fields:
+                if uses_field_type(field.field_type):
+                    return True
+            for nested_union in message.nested_unions:
+                if any(
+                    uses_field_type(field.field_type) for field in nested_union.fields
+                ):
+                    return True
+            return any(uses_message(nested) for nested in message.nested_messages)
+
+        if any(
+            uses_field_type(field.field_type)
+            for union in self.schema.unions
+            for field in union.fields
+        ):
+            return True
+        return any(uses_message(message) for message in self.schema.messages)
+
     def generate(self) -> List[GeneratedFile]:
         """Generate JavaScript files for the schema."""
         return [self.generate_file()]
@@ -806,11 +842,6 @@ def _field_type_expr(
         """Return the Fory JS runtime ``Type.xxx()`` expression for a field type."""
         parent_stack = parent_stack or []
         if isinstance(field_type, PrimitiveType):
-            if field_type.kind == PrimitiveKind.DECIMAL:
-                raise ValueError(
-                    "decimal is not supported by the JavaScript runtime. "
-                    "Use a different type or wait for runtime support."
-                )
             expr = self.PRIMITIVE_RUNTIME_MAP.get(field_type.kind)
             if expr is None:
                 return "Type.any()"
@@ -826,11 +857,6 @@ def _field_type_expr(
                 return self.PRIMITIVE_RUNTIME_MAP[shorthand_map[lower]]
             for pk in PrimitiveKind:
                 if pk.value == lower:
-                    if pk == PrimitiveKind.DECIMAL:
-                        raise ValueError(
-                            "decimal is not supported by the JavaScript runtime. "
-                            "Use a different type or wait for runtime support."
-                        )
                     expr = self.PRIMITIVE_RUNTIME_MAP.get(pk)
                     if expr is None:
                         raise ValueError(

compiler/fory_compiler/generators/python.py

@@ -68,6 +68,7 @@ class PythonGenerator(BaseGenerator):
         PrimitiveKind.BYTES: "bytes",
         PrimitiveKind.DATE: "datetime.date",
         PrimitiveKind.TIMESTAMP: "datetime.datetime",
+        PrimitiveKind.DECIMAL: "decimal.Decimal",
         PrimitiveKind.ANY: "Any",
     }
 
@@ -138,6 +139,7 @@ class PythonGenerator(BaseGenerator):
         PrimitiveKind.BYTES: 'b""',
         PrimitiveKind.DATE: "None",
         PrimitiveKind.TIMESTAMP: "None",
+        PrimitiveKind.DECIMAL: 'decimal.Decimal("0")',
         PrimitiveKind.ANY: "None",
     }
 
@@ -962,6 +964,8 @@ def collect_imports(
         if isinstance(field_type, PrimitiveType):
             if field_type.kind in (PrimitiveKind.DATE, PrimitiveKind.TIMESTAMP):
                 imports.add("import datetime")
+            elif field_type.kind == PrimitiveKind.DECIMAL:
+                imports.add("import decimal")
             elif field_type.kind == PrimitiveKind.ANY:
                 imports.add("from typing import Any")
 

compiler/fory_compiler/generators/rust.py

@@ -67,6 +67,7 @@ class RustGenerator(BaseGenerator):
         PrimitiveKind.BYTES: "Vec<u8>",
         PrimitiveKind.DATE: "chrono::NaiveDate",
         PrimitiveKind.TIMESTAMP: "chrono::NaiveDateTime",
+        PrimitiveKind.DECIMAL: "fory::Decimal",
         PrimitiveKind.ANY: "Box<dyn Any>",
     }
 

compiler/fory_compiler/generators/swift.py

@@ -65,8 +65,9 @@ class SwiftGenerator(BaseGenerator):
         PrimitiveKind.FLOAT64: "Double",
         PrimitiveKind.STRING: "String",
         PrimitiveKind.BYTES: "Data",
-        PrimitiveKind.DATE: "ForyDate",
-        PrimitiveKind.TIMESTAMP: "ForyTimestamp",
+        PrimitiveKind.DATE: "LocalDate",
+        PrimitiveKind.TIMESTAMP: "Date",
+        PrimitiveKind.DECIMAL: "Decimal",
         PrimitiveKind.ANY: "Any",
     }
 
@@ -963,12 +964,13 @@ def generate_message_fields(
 
             encoding = self.field_encoding_argument(field)
             field_id = self.message_field_id_argument(field)
-            if field_id is not None and encoding is not None:
-                lines.append(f"{ind}@ForyField(id: {field_id}, encoding: {encoding})")
-            elif field_id is not None:
-                lines.append(f"{ind}@ForyField(id: {field_id})")
-            elif encoding is not None:
-                lines.append(f"{ind}@ForyField(encoding: {encoding})")
+            attr_parts: List[str] = []
+            if field_id is not None:
+                attr_parts.append(f"id: {field_id}")
+            if encoding is not None:
+                attr_parts.append(f"encoding: {encoding}")
+            if attr_parts:
+                lines.append(f"{ind}@ForyField({', '.join(attr_parts)})")
 
             field_type = self.field_swift_type(field, lineage)
             weak_prefix = "weak " if self.is_weak_ref_field(field) else ""

compiler/fory_compiler/tests/test_dart_generator.py

@@ -143,6 +143,26 @@ def test_dart_generator_uses_typed_lists_for_non_nullable_primitive_lists():
     assert "factory ValueUnion.values(Uint32List value)" in file.content
 
 
+def test_dart_generator_supports_decimal_fields_and_unions():
+    file = generate_dart(
+        """
+        package demo;
+
+        message Money [id=100] {
+            decimal amount = 1;
+        }
+
+        union ValueUnion [id=101] {
+            decimal amount = 1;
+            Money money = 2;
+        }
+        """
+    )
+
+    assert "Decimal amount = const Decimal.zero();" in file.content
+    assert "factory ValueUnion.amount(Decimal value)" in file.content
+
+
 def test_dart_generator_emits_container_ref_annotations_for_builder_metadata():
     file = generate_dart(
         """

compiler/fory_compiler/tests/test_generated_code.py

@@ -543,6 +543,31 @@ def test_java_repeated_float16_generation_uses_float16_list():
     assert "private Float16List vals;" in java_output
 
 
+def test_cpp_generator_supports_decimal_fields_and_unions():
+    schema = parse_fdl(
+        dedent(
+            """
+            package gen;
+
+            message Money {
+                decimal amount = 1;
+            }
+
+            union Value {
+                decimal amount = 1;
+                Money money = 2;
+            }
+            """
+        )
+    )
+
+    cpp_output = render_files(generate_files(schema, CppGenerator))
+    assert '#include "fory/serialization/decimal_serializers.h"' in cpp_output
+    assert "const fory::serialization::Decimal& amount() const" in cpp_output
+    assert "std::variant<fory::serialization::Decimal, Money> value_" in cpp_output
+    assert "(fory::serialization::Decimal, amount, fory::F(1))" in cpp_output
+
+
 def test_java_enum_generation_uses_fory_enum_ids():
     schema = parse_fdl(
         dedent(

compiler/fory_compiler/tests/test_javascript_codegen.py

@@ -219,6 +219,29 @@ def test_javascript_collection_types():
     assert "config: Map<string, number>;" in output
 
 
+def test_javascript_decimal_generation_uses_runtime_decimal_type():
+    source = dedent(
+        """
+        package example;
+
+        message Money [id=100] {
+            decimal amount = 1;
+        }
+
+        union Value [id=101] {
+            decimal amount = 1;
+            Money money = 2;
+        }
+        """
+    )
+    output = generate_javascript(source)
+
+    assert "import { Decimal } from '@apache-fory/core';" in output
+    assert "amount: Decimal;" in output
+    assert "{ case: ValueCase.AMOUNT; value: Decimal }" in output
+    assert "amount: Type.decimal()" in output
+
+
 def test_javascript_map_key_fallback_to_map():
     """Test that map keys not valid for Record use Map<K, V> instead."""
     source = dedent(