Fix false 91x alarm on await in genexp target.

Author: jakkdl

flake8_trio/visitors/visitor91x.py

@@ -769,9 +769,11 @@ def visit_CompFor(self, node: cst.CompFor):
 
         return False
 
-    # We don't have any logic on if generators are guaranteed to unroll, so always
-    # ignore their content by not visiting subnodes.
+    # The generator target will be immediately evaluated, but the other
+    # elements will be lazily evaluated as the generator is consumed so we don't
+    # visit them as any checkpoints in them are not guaranteed to execute.
     def visit_GeneratorExp(self, node: cst.GeneratorExp):
+        node.for_in.iter.visit(self)
         return False
 
     def visit_Import(self, node: cst.Import):

tests/autofix_files/trio910.py

@@ -583,3 +583,19 @@ async def foo_comprehension_2():  # error: 0, "exit", Statement("function defini
 
 async def foo_comprehension_3():
     [... async for x in bar()]
+
+
+# Issue #714
+# (await x async for y in await z)
+#  ^       ^              ^ this always runs!
+#  ^       ^ this might not run
+#  ^ this might not run
+
+
+async def await_in_gen_target():
+    (print(x) for x in await foo())
+
+
+async def await_everywhere_except_gen_target():  # error: 0, "exit", Statement("function definition", lineno)
+    (await x async for x in bar())
+    await trio.lowlevel.checkpoint()

tests/autofix_files/trio910.py.diff

@@ -205,3 +205,8 @@
 
 
  async def foo_comprehension_3():
+@@ x,3 x,4 @@
+
+ async def await_everywhere_except_gen_target():  # error: 0, "exit", Statement("function definition", lineno)
+     (await x async for x in bar())
++    await trio.lowlevel.checkpoint()

tests/eval_files/trio910.py

@@ -555,3 +555,18 @@ async def foo_comprehension_2():  # error: 0, "exit", Statement("function defini
 
 async def foo_comprehension_3():
     [... async for x in bar()]
+
+
+# Issue #714
+# (await x async for y in await z)
+#  ^       ^              ^ this always runs!
+#  ^       ^ this might not run
+#  ^ this might not run
+
+
+async def await_in_gen_target():
+    (print(x) for x in await foo())
+
+
+async def await_everywhere_except_gen_target():  # error: 0, "exit", Statement("function definition", lineno)
+    (await x async for x in bar())