bpo-35975: Support parsing earlier minor versions of Python 3 (GH-12086)
This adds a `feature_version` flag to `ast.parse()` (documented) and `compile()` (hidden) that allow tweaking the parser to support older versions of the grammar. In particular if `feature_version` is 5 or 6, the hacks for the `async` and `await` keyword from PEP 492 are reinstated. (For 7 or higher, these are unconditionally treated as keywords, but they are still special tokens rather than `NAME` tokens that the parser driver recognizes.)
https://bugs.python.org/issue35975
diff --git a/Parser/token.c b/Parser/token.c
index 228ecff..a489668 100644
--- a/Parser/token.c
+++ b/Parser/token.c
@@ -61,6 +61,8 @@
"ELLIPSIS",
"COLONEQUAL",
"OP",
+ "AWAIT",
+ "ASYNC",
"TYPE_IGNORE",
"TYPE_COMMENT",
"<ERRORTOKEN>",