Preliminary support for future nested scopes

compile.h: #define NESTED_SCOPES_DEFAULT 0 for Python 2.1
           __future__ feature name: "nested_scopes"

symtable.h: Add st_nested_scopes slot.  Define flags to track exec and
    import star.

Lib/test/test_scope.py: requires nested scopes

compile.c: Fiddle with error messages.

    Reverse the sense of ste_optimized flag on
    PySymtableEntryObjects.  If it is true, there is an optimization
    conflict.

    Modify get_ref_type to respect st_nested_scopes flags.

    Refactor symtable_load_symbols() into several smaller functions,
    which use struct symbol_info to share variables.  In new function
    symtable_update_flags(), raise an error or warning for import * or
    bare exec that conflicts with nested scopes.  Also, modify handle
    for free variables to respect st_nested_scopes flag.

    In symtable_init() assign st_nested_scopes flag to
    NESTED_SCOPES_DEFAULT (defined in compile.h).

    Add preliminary and often incorrect implementation of
    symtable_check_future().

    Add symtable_lookup() helper for future use.

Include/compile.h

@@ -7,6 +7,9 @@
 extern "C" {
 #endif
 
+#define NESTED_SCOPES_DEFAULT 0
+#define FUTURE_NESTED_SCOPES "nested_scopes"
+
 /* Bytecode object */
 typedef struct {
     PyObject_HEAD

Include/symtable.h

@@ -20,6 +20,7 @@ struct _symtable_entry;
 
 struct symtable {
 	int st_pass;             /* pass == 1 or 2 */
+	int st_nested_scopes;    /* true if nested scopes are enabled */
 	char *st_filename;       /* name of file being compiled */
 	struct _symtable_entry *st_cur; /* current symbol table entry */
 	PyObject *st_symbols;    /* dictionary of symbol table entries */
@@ -40,7 +41,7 @@ typedef struct _symtable_entry {
 	PyObject *ste_children;  /* list of child ids */
 	int ste_type;            /* module, class, or function */
 	int ste_lineno;          /* first line of scope */
-	int ste_optimized;       /* true if namespace is optimized */
+	int ste_optimized;       /* true if namespace can't be optimized */
 	int ste_nested;          /* true if scope is nested */
 	int ste_child_free;      /* true if a child scope has free variables,
 				    including free refs to globals */
@@ -84,6 +85,10 @@ DL_IMPORT(void) PySymtable_Free(struct symtable *);
 #define FREE 4
 #define CELL 5
 
+#define OPT_IMPORT_STAR 1
+#define OPT_EXEC 2
+#define OPT_BARE_EXEC 4
+
 #ifdef __cplusplus
 }
 #endif

Lib/test/test_scope.py

+from __future__ import nested_scopes
+
 from test.test_support import verify, TestFailed, check_syntax
 
 print "1. simple nesting"

Python/symtable.c

@@ -43,7 +43,7 @@ PySymtableEntry_New(struct symtable *st, char *name, int type, int lineno)
 	    goto fail;
 	ste->ste_children = v;
 
-	ste->ste_optimized = 1;
+	ste->ste_optimized = 0;
 	ste->ste_lineno = lineno;
 	switch (type) {
 	case funcdef: