gh-123539: Improve SyntaxError msg for import as with not a name

Author: sobolevn

Grammar/python.gram

@@ -218,15 +218,17 @@ import_from_targets[asdl_alias_seq*]:
 import_from_as_names[asdl_alias_seq*]:
     | a[asdl_alias_seq*]=','.import_from_as_name+ { a }
 import_from_as_name[alias_ty]:
-    | a=NAME b=['as' z=NAME { z }] { _PyAST_alias(a->v.Name.id,
-                                               (b) ? ((expr_ty) b)->v.Name.id : NULL,
-                                               EXTRA) }
+    | a=NAME 'as' b=NAME &(',' | ')' | NEWLINE) { 
+        _PyAST_alias(a->v.Name.id, b->v.Name.id, EXTRA) }
+    | invalid_import_from_as_name
+    | a=NAME { _PyAST_alias(a->v.Name.id, NULL, EXTRA) }
 dotted_as_names[asdl_alias_seq*]:
     | a[asdl_alias_seq*]=','.dotted_as_name+ { a }
 dotted_as_name[alias_ty]:
-    | a=dotted_name b=['as' z=NAME { z }] { _PyAST_alias(a->v.Name.id,
-                                                      (b) ? ((expr_ty) b)->v.Name.id : NULL,
-                                                      EXTRA) }
+    | a=dotted_name 'as' b=NAME &(',' | NEWLINE) { 
+        _PyAST_alias(a->v.Name.id, b->v.Name.id, EXTRA) }
+    | invalid_dotted_as_name
+    | a=dotted_name { _PyAST_alias(a->v.Name.id, NULL, EXTRA) }
 dotted_name[expr_ty]:
     | a=dotted_name '.' b=NAME { _PyPegen_join_names_with_dot(p, a, b) }
     | NAME
@@ -1321,6 +1323,14 @@ invalid_import_from_targets:
         RAISE_SYNTAX_ERROR("trailing comma not allowed without surrounding parentheses") }
     | token=NEWLINE { 
         RAISE_SYNTAX_ERROR_STARTING_FROM(token, "Expected one or more names after 'import'") }
+invalid_dotted_as_name:
+    | dotted_name 'as' a=expression {
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, 
+            "cannot use %s as import target", _PyPegen_get_expr_name(a)) }
+invalid_import_from_as_name:
+    | NAME 'as' a=expression {
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, 
+            "cannot use %s as import target", _PyPegen_get_expr_name(a)) }
 
 invalid_with_stmt:
     | ['async'] 'with' ','.(expression ['as' star_target])+ NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }

Lib/test/test_syntax.py

@@ -1832,6 +1832,56 @@
 Traceback (most recent call last):
 SyntaxError: Expected one or more names after 'import'
 
+>>> import a as b.c
+Traceback (most recent call last):
+SyntaxError: cannot use attribute as import target
+
+>>> import a.b as (a, b)
+Traceback (most recent call last):
+SyntaxError: cannot use tuple as import target
+
+>>> import a, a.b as 1
+Traceback (most recent call last):
+SyntaxError: cannot use literal as import target
+
+>>> import a.b as 'a', a
+Traceback (most recent call last):
+SyntaxError: cannot use literal as import target
+
+>>> from a import (b as c.d)
+Traceback (most recent call last):
+SyntaxError: cannot use attribute as import target
+
+>>> from a import b as 1
+Traceback (most recent call last):
+SyntaxError: cannot use literal as import target
+
+>>> from a import (
+...   b as f())
+Traceback (most recent call last):
+SyntaxError: cannot use function call as import target
+
+>>> from a import (
+...   b as [],
+... )
+Traceback (most recent call last):
+SyntaxError: cannot use list as import target
+
+>>> from a import (
+...   b,
+...   c as ()
+... )
+Traceback (most recent call last):
+SyntaxError: cannot use tuple as import target
+
+>>> from a import b, с as d[e]
+Traceback (most recent call last):
+SyntaxError: cannot use subscript as import target
+
+>>> from a import с as d[e], b
+Traceback (most recent call last):
+SyntaxError: cannot use subscript as import target
+
 >>> (): int
 Traceback (most recent call last):
 SyntaxError: only single target (not tuple) can be annotated
@@ -2857,6 +2907,26 @@ def test_match_stmt_invalid_as_expr(self):
             end_offset=15 + len("obj.attr"),
         )
 
+    def test_invalid_import_stmt_as_expr(self):
+        self._check_error(
+            "import a as obj.attr",
+            errtext="cannot use attribute as import target",
+            lineno=1,
+            end_lineno=1,
+            offset=13,
+            end_offset=13 + len("obj.attr"),
+        )
+
+    def test_invalid_import_from_stmt_as_expr(self):
+        self._check_error(
+            "from a import b as obj.attr",
+            errtext="cannot use attribute as import target",
+            lineno=1,
+            end_lineno=1,
+            offset=20,
+            end_offset=20 + len("obj.attr"),
+        )
+
 
 def load_tests(loader, tests, pattern):
     tests.addTest(doctest.DocTestSuite())

Misc/NEWS.d/next/Core_and_Builtins/2024-09-03-15-15-51.gh-issue-123539.RKQS0S.rst

@@ -0,0 +1 @@
+Improve :exc:`SyntaxError` message for using ``import as`` with not a name.