py/objgenerator: Allow pend_throw to an unstarted generator.

Replace the is_running field with a tri-state variable to indicate
running/not-running/pending-exception.

Update tests to cover the various cases.

This allows cancellation in uasyncio even if the coroutine hasn't been
executed yet.  Fixes #5242

1 files changed, 73 insertions, 3 deletions

diff --git a/tests/basics/generator_pend_throw.py b/tests/basics/generator_pend_throw.py
index f00ff793b..ae8c21189 100644
--- a/tests/basics/generator_pend_throw.py
+++ b/tests/basics/generator_pend_throw.py
@@ -13,6 +13,7 @@ except AttributeError:
     raise SystemExit
 
 
+# Verify that an injected exception will be raised from next().
 print(next(g))
 print(next(g))
 g.pend_throw(ValueError())
@@ -25,7 +26,76 @@ except Exception as e:
 
 print("ret was:", v)
 
+
+# Verify that pend_throw works on an unstarted coroutine.
+g = gen()
+g.pend_throw(OSError())
+try:
+    next(g)
+except Exception as e:
+    print("raised", repr(e))
+
+
+# Verify that you can't resume the coroutine from within the running coroutine.
+def gen_next():
+    next(g)
+    yield 1
+
+g = gen_next()
+
+try:
+    next(g)
+except Exception as e:
+    print("raised", repr(e))
+
+
+# Verify that you can't pend_throw from within the running coroutine.
+def gen_pend_throw():
+    g.pend_throw(ValueError())
+    yield 1
+
+g = gen_pend_throw()
+
+try:
+    next(g)
+except Exception as e:
+    print("raised", repr(e))
+
+
+# Verify that the pend_throw exception can be ignored.
+class CancelledError(Exception):
+    pass
+
+def gen_cancelled():
+    for i in range(5):
+        try:
+            yield i
+        except CancelledError:
+            print('ignore CancelledError')
+
+g = gen_cancelled()
+print(next(g))
+g.pend_throw(CancelledError())
+print(next(g))
+# ...but not if the generator hasn't started.
+g = gen_cancelled()
+g.pend_throw(CancelledError())
 try:
-    gen().pend_throw(ValueError())
-except TypeError:
-    print("TypeError")
+    next(g)
+except Exception as e:
+    print("raised", repr(e))
+
+
+# Verify that calling pend_throw returns the previous exception.
+g = gen()
+next(g)
+print(repr(g.pend_throw(CancelledError())))
+print(repr(g.pend_throw(OSError)))
+
+
+# Verify that you can pend_throw(None) to cancel a previous pend_throw.
+g = gen()
+next(g)
+g.pend_throw(CancelledError())
+print(repr(g.pend_throw(None)))
+print(next(g))