refactor: only set annotations if datclass init

Signed-off-by: Nathaniel Starkman <nstarman@users.noreply.github.com>

Author: nstarman

equinox/_module.py

@@ -300,27 +300,28 @@ def __new__(
         # checkers.
         # Note that mutating the `__init__.__annotations__` is okay, as it was created
         # by the dataclass decorator on the previous line, so nothing else owns it.
-        for f in dataclasses.fields(cls):
-            if f.name not in cls.__init__.__annotations__:
-                continue  # Odd behaviour, so skip.
+        if has_dataclass_init:
+            for f in dataclasses.fields(cls):
+                if not f.init:
+                    continue
 
-            if (converter := f.metadata.get("converter")) is None:
-                continue  # No converter, so skip.
+                if (converter := f.metadata.get("converter")) is None:
+                    continue  # No converter, so skip.
 
-            try:
-                signature = inspect.signature(converter)
-            except ValueError:
-                # e.g. `inspect.signature(str)` fails
-                converter_annotation = Any
-            else:
-                parameters = list(signature.parameters.values())
-                if len(parameters) == 0:
-                    # No idea what happened, but play it safe.
+                try:
+                    signature = inspect.signature(converter)
+                except ValueError:
+                    # e.g. `inspect.signature(str)` fails
                     converter_annotation = Any
                 else:
-                    converter_annotation = parameters[0].annotation
-                    if converter_annotation is inspect.Signature.empty:
+                    parameters = list(signature.parameters.values())
+                    if len(parameters) == 0:
+                        # No idea what happened, but play it safe.
                         converter_annotation = Any
+                    else:
+                        converter_annotation = parameters[0].annotation
+                        if converter_annotation is inspect.Signature.empty:
+                            converter_annotation = Any
                 cls.__init__.__annotations__[f.name] = converter_annotation
 
         # Registering here records that the `dataclass(...)` call has happened.