Work towards feature_version support

Visible behavior:

- Issue error for `X @ Y` (matrix multiply) if c_feature_version < 5

- Add optional feature_version kw arg to ast.parse() (default -1 which
  implies PY_MINOR_VERSION)

- Add feature_version: int = -1 to compile() (via Argument Clinic);
  this sets cf_feature_version to the given value if >= 0, else
  defaults to PY_MINOR_VERSION

Implementation:

- Add PyAST_obj2mod_ex(): like PyAST_obj2mod() but with feature_version arg;
  the latter calls the former with PY_MINOR_VERSION

- Add cf_feature_version to PyCompilerFlags structure;
  initialized to PY_MINOR_VERSION everywhere

- Add c_feature_version to struct compiling; initialize from
  cf_feature_version

- Add 'c' argument to get_operator()

- In builtin eval() and exec(), default to PY_MINOR_VERSION

TODO:

- Put version-dependent ASYNC/AWAIT keyword scanning back

- Reject async functions, await expressions, and async for/with in minor versions < 5

- Reject async comprehensions in minor versions < 6

- Reject underscores in numeric literals in minor versions < 6

- Reject variable annotations in minor versions < 6

- Reject `X @= Y` in minor versions < 5

1 files changed, 4 insertions, 0 deletions

diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 906877a0a8..ae6778d8a5 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -105,6 +105,7 @@ PyRun_InteractiveLoopFlags(FILE *fp, const char *filename_str, PyCompilerFlags *
     if (flags == NULL) {
         flags = &local_flags;
         local_flags.cf_flags = 0;
+        local_flags.cf_feature_version = PY_MINOR_VERSION;
     }
     v = _PySys_GetObjectId(&PyId_ps1);
     if (v == NULL) {
@@ -1165,6 +1166,7 @@ Py_SymtableStringObject(const char *str, PyObject *filename, int start)
         return NULL;
 
     flags.cf_flags = 0;
+    flags.cf_feature_version = PY_MINOR_VERSION;
     mod = PyParser_ASTFromStringObject(str, filename, start, &flags, arena);
     if (mod == NULL) {
         PyArena_Free(arena);
@@ -1204,6 +1206,7 @@ PyParser_ASTFromStringObject(const char *s, PyObject *filename, int start,
                                          &iflags);
     if (flags == NULL) {
         localflags.cf_flags = 0;
+        localflags.cf_feature_version = PY_MINOR_VERSION;
         flags = &localflags;
     }
     if (n) {
@@ -1249,6 +1252,7 @@ PyParser_ASTFromFileObject(FILE *fp, PyObject *filename, const char* enc,
                                        start, ps1, ps2, &err, &iflags);
     if (flags == NULL) {
         localflags.cf_flags = 0;
+        localflags.cf_feature_version = PY_MINOR_VERSION;
         flags = &localflags;
     }
     if (n) {