Support numeric constraints for Decimal types

.devcontainer/devcontainer.json

@@ -0,0 +1,26 @@
+{
+    "name": "jcrist/msgspec",
+    "image": "mcr.microsoft.com/devcontainers/python:3.12-bookworm",
+    "postCreateCommand": "scripts/install.sh",
+    "customizations": {
+        "vscode": {
+            "extensions": [
+                "charliermarsh.ruff",
+                "ms-python.python",
+                "ms-vscode.cpptools"
+            ],
+            "settings": {
+                "C_Cpp.default.includePath": [
+                    "/usr/local/include/**"
+                ],
+                "C_Cpp.formatting": "disabled",
+                "python.testing.pytestArgs": [
+                    "-v",
+                    "tests/"
+                ],
+                "python.testing.pytestEnabled": true,
+                "python.testing.unittestEnabled": false
+            }
+        }
+    }
+}

docs/source/constraints.rst

@@ -76,7 +76,7 @@ The following constraints are supported:
 Numeric Constraints
 -------------------
 
-These constraints are valid on `int` or `float` types:
+These constraints are valid on `int`, `float`, or `decimal.Decimal` types:
 
 - ``ge``: The value must be greater than or equal to ``ge``.
 - ``gt``: The value must be greater than ``gt``.
@@ -88,23 +88,33 @@ These constraints are valid on `int` or `float` types:
 
     >>> import msgspec
 
+    >>> from decimal import Decimal
+
     >>> from typing import Annotated
 
     >>> msgspec.json.decode(b'-1', type=Annotated[int, msgspec.Meta(ge=0)])
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     msgspec.ValidationError: Expected `int` >= 0
 
-.. warning::
+    >>> msgspec.json.decode(b'0.3', type=Annotated[Decimal, msgspec.Meta(multiple_of=Decimal('0.1'))])
+    Decimal('0.3')
+
+.. note::
 
     While ``multiple_of`` works on ``float`` types, we don't recommend
-    specifying *non-integral* ``multiple_of`` constraints, as they may be
-    erroneously marked as invalid due to floating point precision issues. For
-    example, annotating a ``float`` type with ``multiple_of=10`` is fine, but
-    ``multiple_of=0.1`` may lead to issues. See `this GitHub issue
+    specifying *non-integral* ``multiple_of`` constraints on them,
+    as they may be erroneously marked as invalid due to floating point
+    precision issues. For example, annotating a ``float`` type with
+    ``multiple_of=10`` is fine, but ``multiple_of=0.1`` may lead to issues.
+    See `this GitHub issue
     <https://github.com/json-schema-org/json-schema-spec/issues/312>`_ for more
     details.
 
+    To address this issue, ``msgspec`` supports specifying ``multiple_of``
+    constraints with `decimal.Decimal` types, that offer arbitrary precision
+    arithmetic.
+
 String Constraints
 ------------------
 

msgspec/__init__.pyi

@@ -1,4 +1,5 @@
 import enum
+from decimal import Decimal
 from typing import (
     Any,
     Callable,
@@ -115,11 +116,11 @@ class Meta:
     def __init__(
         self,
         *,
-        gt: Union[int, float, None] = None,
-        ge: Union[int, float, None] = None,
-        lt: Union[int, float, None] = None,
-        le: Union[int, float, None] = None,
-        multiple_of: Union[int, float, None] = None,
+        gt: Union[int, float, Decimal, None] = None,
+        ge: Union[int, float, Decimal, None] = None,
+        lt: Union[int, float, Decimal, None] = None,
+        le: Union[int, float, Decimal, None] = None,
+        multiple_of: Union[int, float, Decimal, None] = None,
         pattern: Union[str, None] = None,
         min_length: Union[int, None] = None,
         max_length: Union[int, None] = None,
@@ -130,11 +131,11 @@ class Meta:
         extra_json_schema: Union[dict, None] = None,
         extra: Union[dict, None] = None,
     ): ...
-    gt: Final[Union[int, float, None]]
-    ge: Final[Union[int, float, None]]
-    lt: Final[Union[int, float, None]]
-    le: Final[Union[int, float, None]]
-    multiple_of: Final[Union[int, float, None]]
+    gt: Final[Union[int, float, Decimal, None]]
+    ge: Final[Union[int, float, Decimal, None]]
+    lt: Final[Union[int, float, Decimal, None]]
+    le: Final[Union[int, float, Decimal, None]]
+    multiple_of: Final[Union[int, float, Decimal, None]]
     pattern: Final[Union[str, None]]
     min_length: Final[Union[int, None]]
     max_length: Final[Union[int, None]]