From 9265d6eab7ad2772c422118bcc0b885633077ea2 Mon Sep 17 00:00:00 2001
From: "Michael J. Sullivan" <sully@msully.net>
Date: Fri, 30 Jan 2026 14:06:56 -0800
Subject: [PATCH] Implement RaiseError

---
 pep.rst                              |  4 +++-
 tests/test_fastapilike_1.py          |  2 +-
 tests/test_type_eval.py              | 26 ++++++++++++++++++++++++++
 typemap/type_eval/__init__.py        |  3 +++
 typemap/type_eval/_eval_operators.py | 25 +++++++++++++++++++++++++
 typemap/typing.py                    | 13 +++++++++++++
 6 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/pep.rst b/pep.rst
index 559ac6c..ac22bcf 100644
--- a/pep.rst
+++ b/pep.rst
@@ -778,10 +778,12 @@ All of the operators in this section are :ref:`lifted over union types
 Raise error
 '''''''''''
 
-* ``RaiseError[S: Literal[str]]``: If this type needs to be evaluated
+* ``RaiseError[S: Literal[str], *Ts]``: If this type needs to be evaluated
   to determine some actual type, generate a type error with the
   provided message.
 
+  Any additional type arguments should be included in the message.
+
 Update class
 ''''''''''''
 
diff --git a/tests/test_fastapilike_1.py b/tests/test_fastapilike_1.py
index 3b79a7f..fbb2172 100644
--- a/tests/test_fastapilike_1.py
+++ b/tests/test_fastapilike_1.py
@@ -78,7 +78,7 @@ class _Default:
 
 type AddInit[T] = NewProtocol[
     InitFnType[T],
-    *Members[T]],
+    *Members[T],
 ]
 
 but we struggle here because typing wants to unpack the Members tuple
diff --git a/tests/test_type_eval.py b/tests/test_type_eval.py
index 9b239d6..2833b9f 100644
--- a/tests/test_type_eval.py
+++ b/tests/test_type_eval.py
@@ -1565,3 +1565,29 @@ def test_type_eval_annotated_03():
 def test_type_eval_annotated_04():
     res = eval_typing(GetAnnotations[GetMemberType[AnnoTest, Literal["b"]]])
     assert res == Literal["blah"]
+
+
+##############
+# RaiseError tests
+
+from typemap.typing import RaiseError
+from typemap.type_eval import TypeMapError
+
+
+def test_raise_error_basic():
+    with pytest.raises(TypeMapError, match="Test error message"):
+        eval_typing(RaiseError[Literal["Test error message"]])
+
+
+def test_raise_error_with_types():
+    with pytest.raises(TypeMapError, match="Broadcast mismatch.*int.*str"):
+        eval_typing(RaiseError[Literal["Broadcast mismatch"], int, str])
+
+
+def test_raise_error_with_literal_types():
+    with pytest.raises(
+        TypeMapError, match="Shape mismatch.*Literal\\[4\\].*Literal\\[3\\]"
+    ):
+        eval_typing(
+            RaiseError[Literal["Shape mismatch"], Literal[4], Literal[3]]
+        )
diff --git a/typemap/type_eval/__init__.py b/typemap/type_eval/__init__.py
index 3d2a217..3c1484e 100644
--- a/typemap/type_eval/__init__.py
+++ b/typemap/type_eval/__init__.py
@@ -14,6 +14,8 @@
 # This one is imported for registering handlers
 from . import _eval_operators  # noqa
 
+from ._eval_operators import TypeMapError
+
 
 __all__ = (
     "eval_typing",
@@ -23,6 +25,7 @@
     "flatten_class",
     "issubtype",
     "issubsimilar",
+    "TypeMapError",
     "_EvalProxy",
     "_get_current_context",
 )
diff --git a/typemap/type_eval/_eval_operators.py b/typemap/type_eval/_eval_operators.py
index df2ac67..cab2d2e 100644
--- a/typemap/type_eval/_eval_operators.py
+++ b/typemap/type_eval/_eval_operators.py
@@ -38,6 +38,7 @@
     Members,
     NewProtocol,
     Param,
+    RaiseError,
     Slice,
     SpecialFormEllipsis,
     StrConcat,
@@ -997,6 +998,30 @@ def func(*args, ctx):
 ##################################################################
 
 
+class TypeMapError(TypeError):
+    """Exception raised when RaiseError is evaluated."""
+
+    pass
+
+
+@type_eval.register_evaluator(RaiseError)
+@_lift_evaluated
+def _eval_RaiseError(msg, *extra_types, ctx):
+    """Evaluate RaiseError by raising a TypeMapError.
+
+    RaiseError[S, *Ts] raises a type error with message S,
+    including the string representations of any extra type arguments.
+    """
+    message = _from_literal(msg)
+    if extra_types:
+        type_strs = ", ".join(repr(t) for t in extra_types)
+        message = f"{message}: {type_strs}"
+    raise TypeMapError(message)
+
+
+##################################################################
+
+
 def _add_quals(typ, quals):
     for qual in (typing.ClassVar, typing.Final):
         if type_eval.issubsimilar(typing.Literal[qual.__name__], quals):
diff --git a/typemap/typing.py b/typemap/typing.py
index 9db378d..ddca390 100644
--- a/typemap/typing.py
+++ b/typemap/typing.py
@@ -179,6 +179,19 @@ class NewProtocol[*T]:
     pass
 
 
+class RaiseError[S: str, *Ts]:
+    """Raise a type error with the given message when evaluated.
+
+    RaiseError[S: Literal[str], *Ts]: If this type needs to be evaluated
+    to determine some actual type, generate a type error with the
+    provided message.
+
+    Any additional type arguments should be included in the message.
+    """
+
+    pass
+
+
 ##################################################################
 
 # TODO: type better