gh-125331: Allow the parser to activate future imports on the fly (#125482)

pablogsal · web-flow · commit 3bd3e09588bf · 2025-02-14T04:54:56.000Z
diff --git a/Grammar/python.gram b/Grammar/python.gram
@@ -207,7 +207,7 @@ import_name[stmt_ty]: 'import' a=dotted_as_names { _PyAST_Import(a, EXTRA) }
 # note below: the ('.' | '...') is necessary because '...' is tokenized as ELLIPSIS
 import_from[stmt_ty]:
     | 'from' a=('.' | '...')* b=dotted_name 'import' c=import_from_targets {
-        _PyAST_ImportFrom(b->v.Name.id, c, _PyPegen_seq_count_dots(a), EXTRA) }
+        _PyPegen_checked_future_import(p, b->v.Name.id, c, _PyPegen_seq_count_dots(a), EXTRA) }
     | 'from' a=('.' | '...')+ 'import' b=import_from_targets {
         _PyAST_ImportFrom(NULL, b, _PyPegen_seq_count_dots(a), EXTRA) }
 import_from_targets[asdl_alias_seq*]:
diff --git a/Lib/test/test_flufl.py b/Lib/test/test_flufl.py
@@ -34,6 +34,32 @@ def test_guido_as_bdfl(self):
         # parser reports the start of the token
         self.assertEqual(cm.exception.offset, 3)
 
+    def test_barry_as_bdfl_look_ma_with_no_compiler_flags(self):
+        # Check that the future import is handled by the parser
+        # even if the compiler flags are not passed.
+        code = "from __future__ import barry_as_FLUFL;2 {0} 3"
+        compile(code.format('<>'), '<BDFL test>', 'exec')
+        with self.assertRaises(SyntaxError) as cm:
+            compile(code.format('!='), '<FLUFL test>', 'exec')
+        self.assertRegex(str(cm.exception), "with Barry as BDFL, use '<>' instead of '!='")
+        self.assertIn('2 != 3', cm.exception.text)
+        self.assertEqual(cm.exception.filename, '<FLUFL test>')
+        self.assertEqual(cm.exception.lineno, 1)
+        self.assertEqual(cm.exception.offset, len(code) - 4)
+
+    def test_barry_as_bdfl_relative_import(self):
+        code = "from .__future__ import barry_as_FLUFL;2 {0} 3"
+        compile(code.format('!='), '<FLUFL test>', 'exec')
+        with self.assertRaises(SyntaxError) as cm:
+            compile(code.format('<>'), '<BDFL test>', 'exec')
+        self.assertRegex(str(cm.exception), "<BDFL test>")
+        self.assertIn('2 <> 3', cm.exception.text)
+        self.assertEqual(cm.exception.filename, '<BDFL test>')
+        self.assertEqual(cm.exception.lineno, 1)
+        self.assertEqual(cm.exception.offset, len(code) - 4)
+
+
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-10-29-23-30-35.gh-issue-125331.quKQ7V.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-10-29-23-30-35.gh-issue-125331.quKQ7V.rst
@@ -0,0 +1,5 @@
+``from __future__ import barry_as_FLUFL`` now works in more contexts,
+including when it is used in files, with the ``-c`` flag, and in the REPL
+when there are multiple statements on the same line. Previously, it worked
+only on subsequent lines in the REPL, and when the appropriate flags were
+passed directly to :func:`compile`. Patch by Pablo Galindo.
diff --git a/Parser/action_helpers.c b/Parser/action_helpers.c
@@ -1694,3 +1694,18 @@ _PyPegen_concatenate_strings(Parser *p, asdl_expr_seq *strings,
     assert(current_pos == n_elements);
     return _PyAST_JoinedStr(values, lineno, col_offset, end_lineno, end_col_offset, p->arena);
 }
+
+stmt_ty
+_PyPegen_checked_future_import(Parser *p, identifier module, asdl_alias_seq * names, int level,
+                  			   int lineno, int col_offset, int end_lineno, int end_col_offset,
+                      		   PyArena *arena) {
+    if (level == 0 && PyUnicode_CompareWithASCIIString(module, "__future__") == 0) {
+        for (Py_ssize_t i = 0; i < asdl_seq_LEN(names); i++) {
+            alias_ty alias = asdl_seq_GET(names, i);
+            if (PyUnicode_CompareWithASCIIString(alias->name, "barry_as_FLUFL") == 0) {
+                p->flags |= PyPARSE_BARRY_AS_BDFL;
+            }
+        }
+    }
+    return _PyAST_ImportFrom(module, names, level, lineno, col_offset, end_lineno, end_col_offset, arena);
+}
diff --git a/Parser/parser.c b/Parser/parser.c
diff --git a/Parser/pegen.h b/Parser/pegen.h
@@ -346,6 +346,8 @@ mod_ty _PyPegen_make_module(Parser *, asdl_stmt_seq *);
 void *_PyPegen_arguments_parsing_error(Parser *, expr_ty);
 expr_ty _PyPegen_get_last_comprehension_item(comprehension_ty comprehension);
 void *_PyPegen_nonparen_genexp_in_call(Parser *p, expr_ty args, asdl_comprehension_seq *comprehensions);
+stmt_ty _PyPegen_checked_future_import(Parser *p, identifier module, asdl_alias_seq *,
+                                       int , int, int , int , int , PyArena *);
 
 // Parser API
 
