Fix duplicate iterators being cached.

tests/test_type_eval.py

@@ -640,7 +640,7 @@ def test_never_is():
     assert d is True
 
 
-def test_eval_iter():
+def test_eval_iter_01():
     d = eval_typing(Iter[tuple[int, str]])
     assert tuple(d) == (int, str)
 
@@ -654,6 +654,22 @@ def test_eval_iter():
     assert tuple(d) == ()
 
 
+type DuplicateTuple[T] = tuple[*[x for x in Iter[T]], *[x for x in Iter[T]]]
+type ConcatTupleWithSelf[T] = ConcatTuples[T, T]
+
+
+def test_eval_iter_02():
+    # ensure iterating duplicate tuples can be iterated multiple times
+    d = eval_typing(ConcatTuples[tuple[int, str], tuple[int, str]])
+    assert d == tuple[int, str, int, str]
+
+    d = eval_typing(DuplicateTuple[tuple[int, str]])
+    assert d == tuple[int, str, int, str]
+
+    d = eval_typing(ConcatTupleWithSelf[tuple[int, str]])
+    assert d == tuple[int, str, int, str]
+
+
 def test_eval_length_01():
     d = eval_typing(Length[tuple[int, str]])
     assert d == Literal[2]

typemap/type_eval/_eval_typing.py

@@ -1,5 +1,6 @@
 import annotationlib
 
+import collections.abc
 import contextlib
 import contextvars
 import dataclasses
@@ -231,7 +232,10 @@ def _eval_types(obj: typing.Any, ctx: EvalContext):
         ctx.resolved |= {x: x for x in child_ctx.known_recursive_types.keys()}
         ctx.known_recursive_types |= child_ctx.known_recursive_types
 
-    ctx.resolved[obj] = evaled
+    # Don't cache iterators as they are stateful and can only be consumed once.
+    # This is important for Iter results that may be used multiple times.
+    if not isinstance(evaled, collections.abc.Iterator):
+        ctx.resolved[obj] = evaled
     return evaled