Improved error messages a little bit, in particular to highlight indi…

…vidual problematic arguments.

jaxtyping/_decorator.py

@@ -379,7 +379,12 @@ def wrapped_fn(*args, **kwargs):
                         raise
                     except Exception as e:
                         argmsg = _get_problem_arg(
-                            param_signature, args, kwargs, module, typechecker
+                            param_signature,
+                            args,
+                            kwargs,
+                            bound.arguments,
+                            module,
+                            typechecker,
                         )
                         try:
                             name = fn.__name__
@@ -390,7 +395,8 @@ def wrapped_fn(*args, **kwargs):
                         msg = (
                             "Type-check error whilst checking the parameters of "
                             f"{name}.{argmsg}\n"
-                            f"Called with arguments: {param_values}\n"
+                            "----------------------\n"
+                            f"Called with parameters: {param_values}\n"
                             f"Parameter annotations: {param_hints}.\n"
                             + _exc_shape_info(memos)
                         )
@@ -440,10 +446,11 @@ def wrapped_fn(*args, **kwargs):
                             msg = (
                                 "Type-check error whilst checking the return value "
                                 f"of {name}.\n"
-                                f"Called with arguments: {param_values}\n"
-                                f"Return value: {return_value}\n"
+                                f"Actual value: {return_value}\n"
+                                f"Expected type: {return_hint}.\n"
+                                "----------------------\n"
+                                f"Called with parameters: {param_values}\n"
                                 f"Parameter annotations: {param_hints}.\n"
-                                f"Return annotation: {return_hint}.\n"
                                 + _exc_shape_info(memos)
                             )
                             if config.jaxtyping_remove_typechecker_stack:
@@ -660,7 +667,7 @@ def _make_argpiece(p, name_to_annotation, name_to_default):
 
 
 def _get_problem_arg(
-    param_signature: inspect.Signature, args, kwargs, module, typechecker
+    param_signature: inspect.Signature, args, kwargs, arguments, module, typechecker
 ) -> str:
     """Determines which argument was likely to be the problematic one responsible for
     raising a type-check error.
@@ -669,13 +676,17 @@ def _get_problem_arg(
     # anyway.
     for keep_name in param_signature.parameters.keys():
         new_parameters = []
+        keep_annotation = sentinel = object()
         for p_name, p in param_signature.parameters.items():
             if p_name == keep_name:
                 new_parameters.append(
                     inspect.Parameter(p.name, p.kind, annotation=p.annotation)
                 )
+                assert keep_annotation is sentinel
+                keep_annotation = _remove_typing(p.annotation)
             else:
                 new_parameters.append(inspect.Parameter(p.name, p.kind))
+        assert keep_annotation is not sentinel
         new_signature = inspect.Signature(new_parameters)
         fn = _make_fn_with_signature(
             "check_single_arg", new_signature, module, output=False
@@ -684,7 +695,12 @@ def _get_problem_arg(
         try:
             fn(*args, **kwargs)
         except Exception:
-            return f"\nThe problem arose whilst typechecking argument '{keep_name}'."
+            keep_value = _pformat(arguments[keep_name], short_self=False)
+            return (
+                f"\nThe problem arose whilst typechecking parameter '{keep_name}'.\n"
+                f"Actual value: {keep_value}\n"
+                f"Expected type: {keep_annotation}."
+            )
     else:
         # Could not localise the problem to a single argument -- probably due to
         # e.g. a mismatched typevar, which each individual argument is okay with.

test/test_messages.py

@@ -14,8 +14,8 @@ def f(x: str, y: str, z: int):
 
     matches = [
         "Type-check error whilst checking the parameters of f",
-        "The problem arose whilst typechecking argument 'z'.",
-        "Called with arguments: {'x': 'hi', 'y': 'bye', 'z': 'not-an-int'}",
+        "The problem arose whilst typechecking parameter 'z'.",
+        "Called with parameters: {'x': 'hi', 'y': 'bye', 'z': 'not-an-int'}",
         r"Parameter annotations: \(x: str, y: str, z: int\).",
     ]
     for match in matches:
@@ -30,8 +30,8 @@ def g(x: Float[Array, "a b"], y: Float[Array, "b c"]):
     y = jnp.zeros((4, 3))
     matches = [
         "Type-check error whilst checking the parameters of g",
-        "The problem arose whilst typechecking argument 'y'.",
-        r"Called with arguments: {'x': f32\[2,3\], 'y': f32\[4,3\]}",
+        "The problem arose whilst typechecking parameter 'y'.",
+        r"Called with parameters: {'x': f32\[2,3\], 'y': f32\[4,3\]}",
         (
             r"Parameter annotations: \(x: Float\[Array, 'a b'\], y: "
             r"Float\[Array, 'b c'\]\)."
@@ -54,9 +54,9 @@ def f(x: PyTree[Any, " T"], y: PyTree[Any, " S"]) -> PyTree[Any, "T S"]:
     y = {"a": 1}
     matches = [
         "Type-check error whilst checking the return value of f",
-        r"Called with arguments: {'x': \(1, 2\), 'y': {'a': 1}}",
-        "Return value: 'foo'",
-        r"Return annotation: PyTree\[Any, \"T S\"\].",
+        r"Called with parameters: {'x': \(1, 2\), 'y': {'a': 1}}",
+        "Actual value: 'foo'",
+        r"Expected type: PyTree\[Any, \"T S\"\].",
         (
             "The current values for each jaxtyping PyTree structure annotation are as "
             "follows."
@@ -82,9 +82,9 @@ class M(eqx.Module):
 
     matches = [
         "Type-check error whilst checking the parameters of M",
-        "The problem arose whilst typechecking argument 'z'.",
+        "The problem arose whilst typechecking parameter 'z'.",
         (
-            r"Called with arguments: {'self': M\(\.\.\.\), 'x': f32\[2,3\], "
+            r"Called with parameters: {'self': M\(\.\.\.\), 'x': f32\[2,3\], "
             r"'y': \(1, \(3, 4\)\), 'z': 'not-an-int'}"
         ),
         (