Ugly. A pile of new xxxFlags() functions, to communicate to the parser

that 'yield' is a keyword.  This doesn't help test_generators at all!  I
don't know why not.  These things do work now (and didn't before this
patch):

1. "from __future__ import generators" now works in a native shell.

2. Similarly "python -i xxx.py" now has generators enabled in the
   shell if xxx.py had them enabled.

3. This program (which was my doctest proxy) works fine:

from __future__ import generators

source = """\
def f():
    yield 1
"""

exec compile(source, "", "single") in globals()
print type(f())

5 files changed, 65 insertions, 14 deletions

diff --git a/Include/parsetok.h b/Include/parsetok.h
index aebc83c..66359d42 100644
--- a/Include/parsetok.h
+++ b/Include/parsetok.h
@@ -17,11 +17,19 @@ typedef struct {
     int expected;
 } perrdetail;
 
+#define PyPARSE_YIELD_IS_KEYWORD	0x0001
+
 extern DL_IMPORT(node *) PyParser_ParseString(char *, grammar *, int,
                                               perrdetail *);
 extern DL_IMPORT(node *) PyParser_ParseFile (FILE *, char *, grammar *, int,
                                              char *, char *, perrdetail *);
 
+extern DL_IMPORT(node *) PyParser_ParseStringFlags(char *, grammar *, int,
+                                              perrdetail *, int);
+extern DL_IMPORT(node *) PyParser_ParseFileFlags(FILE *, char *, grammar *,
+						 int, char *, char *,
+						 perrdetail *, int);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/Include/pythonrun.h b/Include/pythonrun.h
index 3877a82..6e9821b 100644
--- a/Include/pythonrun.h
+++ b/Include/pythonrun.h
@@ -45,6 +45,9 @@ DL_IMPORT(int) PyRun_InteractiveLoopFlags(FILE *, char *, PyCompilerFlags *);
 
 DL_IMPORT(struct _node *) PyParser_SimpleParseString(char *, int);
 DL_IMPORT(struct _node *) PyParser_SimpleParseFile(FILE *, char *, int);
+DL_IMPORT(struct _node *) PyParser_SimpleParseStringFlags(char *, int, int);
+DL_IMPORT(struct _node *) PyParser_SimpleParseFileFlags(FILE *, char *,
+							int, int);
 
 DL_IMPORT(PyObject *) PyRun_String(char *, int, PyObject *, PyObject *);
 DL_IMPORT(PyObject *) PyRun_File(FILE *, char *, int, PyObject *, PyObject *);
diff --git a/Lib/doctest.py b/Lib/doctest.py
index b59a68a..fc826df 100644
--- a/Lib/doctest.py
+++ b/Lib/doctest.py
@@ -348,6 +348,8 @@ Test passed.
 # 0,9,7    9-Feb-2001
 #    string method conversion
 
+from __future__ import generators
+
 __version__ = 0, 9, 7
 
 import types
diff --git a/Parser/parsetok.c b/Parser/parsetok.c
index b68fbd7..6017e5f 100644
--- a/Parser/parsetok.c
+++ b/Parser/parsetok.c
@@ -13,13 +13,19 @@ int Py_TabcheckFlag;
 
 
 /* Forward */
-static node *parsetok(struct tok_state *, grammar *, int, perrdetail *);
+static node *parsetok(struct tok_state *, grammar *, int, perrdetail *, int);
 
 /* Parse input coming from a string.  Return error code, print some errors. */
-
 node *
 PyParser_ParseString(char *s, grammar *g, int start, perrdetail *err_ret)
 {
+	return PyParser_ParseStringFlags(s, g, start, err_ret, 0);
+}
+
+node *
+PyParser_ParseStringFlags(char *s, grammar *g, int start,
+		          perrdetail *err_ret, int flags)
+{
 	struct tok_state *tok;
 
 	err_ret->error = E_OK;
@@ -42,7 +48,7 @@ PyParser_ParseString(char *s, grammar *g, int start, perrdetail *err_ret)
 			tok->alterror++;
 	}
 
-	return parsetok(tok, g, start, err_ret);
+	return parsetok(tok, g, start, err_ret, flags);
 }
 
 
@@ -52,6 +58,14 @@ node *
 PyParser_ParseFile(FILE *fp, char *filename, grammar *g, int start,
 		   char *ps1, char *ps2, perrdetail *err_ret)
 {
+	return PyParser_ParseFileFlags(fp, filename, g, start, ps1, ps2,
+				       err_ret, 0);
+}
+
+node *
+PyParser_ParseFileFlags(FILE *fp, char *filename, grammar *g, int start,
+			char *ps1, char *ps2, perrdetail *err_ret, int flags)
+{
 	struct tok_state *tok;
 
 	err_ret->error = E_OK;
@@ -72,14 +86,15 @@ PyParser_ParseFile(FILE *fp, char *filename, grammar *g, int start,
 	}
 
 
-	return parsetok(tok, g, start, err_ret);
+	return parsetok(tok, g, start, err_ret, flags);
 }
 
 /* Parse input coming from the given tokenizer structure.
    Return error code. */
 
 static node *
-parsetok(struct tok_state *tok, grammar *g, int start, perrdetail *err_ret)
+parsetok(struct tok_state *tok, grammar *g, int start, perrdetail *err_ret,
+	 int flags)
 {
 	parser_state *ps;
 	node *n;
@@ -90,6 +105,8 @@ parsetok(struct tok_state *tok, grammar *g, int start, perrdetail *err_ret)
 		err_ret->error = E_NOMEM;
 		return NULL;
 	}
+	if (flags & PyPARSE_YIELD_IS_KEYWORD)
+		ps->p_generators = 1;
 
 	for (;;) {
 		char *a, *b;
diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 0412b7e..1d20deb 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -533,6 +533,7 @@ PyRun_InteractiveOneFlags(FILE *fp, char *filename, PyCompilerFlags *flags)
 	node *n;
 	perrdetail err;
 	char *ps1 = "", *ps2 = "";
+
 	v = PySys_GetObject("ps1");
 	if (v != NULL) {
 		v = PyObject_Str(v);
@@ -549,8 +550,11 @@ PyRun_InteractiveOneFlags(FILE *fp, char *filename, PyCompilerFlags *flags)
 		else if (PyString_Check(w))
 			ps2 = PyString_AsString(w);
 	}
-	n = PyParser_ParseFile(fp, filename, &_PyParser_Grammar,
-			       Py_single_input, ps1, ps2, &err);
+	n = PyParser_ParseFileFlags(fp, filename, &_PyParser_Grammar,
+			    	    Py_single_input, ps1, ps2, &err,
+			    	    (flags &&
+			    	     flags->cf_flags & PyCF_GENERATORS) ?
+			    	    	PyPARSE_YIELD_IS_KEYWORD : 0);
 	Py_XDECREF(v);
 	Py_XDECREF(w);
 	if (n == NULL) {
@@ -1017,7 +1021,9 @@ PyObject *
 PyRun_FileExFlags(FILE *fp, char *filename, int start, PyObject *globals,
 		  PyObject *locals, int closeit, PyCompilerFlags *flags)
 {
-	node *n = PyParser_SimpleParseFile(fp, filename, start);
+	node *n = PyParser_SimpleParseFileFlags(fp, filename, start,
+			(flags && flags->cf_flags & PyCF_GENERATORS) ?
+				PyPARSE_YIELD_IS_KEYWORD : 0);
 	if (closeit)
 		fclose(fp);
 	return run_err_node(n, filename, globals, locals, flags);
@@ -1101,7 +1107,9 @@ Py_CompileStringFlags(char *str, char *filename, int start,
 {
 	node *n;
 	PyCodeObject *co;
-	n = PyParser_SimpleParseString(str, start);
+	n = PyParser_SimpleParseStringFlags(str, start,
+		(flags && flags->cf_flags & PyCF_GENERATORS) ?
+			PyPARSE_YIELD_IS_KEYWORD : 0);
 	if (n == NULL)
 		return NULL;
 	co = PyNode_CompileFlags(n, filename, flags);
@@ -1125,30 +1133,43 @@ Py_SymtableString(char *str, char *filename, int start)
 /* Simplified interface to parsefile -- return node or set exception */
 
 node *
-PyParser_SimpleParseFile(FILE *fp, char *filename, int start)
+PyParser_SimpleParseFileFlags(FILE *fp, char *filename, int start, int flags)
 {
 	node *n;
 	perrdetail err;
-	n = PyParser_ParseFile(fp, filename, &_PyParser_Grammar, start,
-				(char *)0, (char *)0, &err);
+	n = PyParser_ParseFileFlags(fp, filename, &_PyParser_Grammar, start,
+					(char *)0, (char *)0, &err, flags);
 	if (n == NULL)
 		err_input(&err);
 	return n;
 }
 
+node *
+PyParser_SimpleParseFile(FILE *fp, char *filename, int start)
+{
+	return PyParser_SimpleParseFileFlags(fp, filename, start, 0);
+}
+
 /* Simplified interface to parsestring -- return node or set exception */
 
 node *
-PyParser_SimpleParseString(char *str, int start)
+PyParser_SimpleParseStringFlags(char *str, int start, int flags)
 {
 	node *n;
 	perrdetail err;
-	n = PyParser_ParseString(str, &_PyParser_Grammar, start, &err);
+	n = PyParser_ParseStringFlags(str, &_PyParser_Grammar, start, &err,
+				      flags);
 	if (n == NULL)
 		err_input(&err);
 	return n;
 }
 
+node *
+PyParser_SimpleParseString(char *str, int start)
+{
+	return PyParser_SimpleParseStringFlags(str, start, 0);
+}
+
 /* Set the error appropriate to the given input error code (see errcode.h) */
 
 static void