gh-129515: Clarify syntax error messages for conditional expressions

Grammar/python.gram

@@ -117,12 +117,12 @@ simple_stmt[stmt_ty] (memo):
     | &'return' return_stmt
     | &('import' | 'from') import_stmt
     | &'raise' raise_stmt
-    | 'pass' { _PyAST_Pass(EXTRA) }
+    | &'pass' pass_stmt
     | &'del' del_stmt
     | &'yield' yield_stmt
     | &'assert' assert_stmt
-    | 'break' { _PyAST_Break(EXTRA) }
-    | 'continue' { _PyAST_Continue(EXTRA) }
+    | &'break' break_stmt
+    | &'continue' continue_stmt
     | &'global' global_stmt
     | &'nonlocal' nonlocal_stmt
 
@@ -181,6 +181,15 @@ raise_stmt[stmt_ty]:
     | 'raise' a=expression b=['from' z=expression { z }] { _PyAST_Raise(a, b, EXTRA) }
     | 'raise' { _PyAST_Raise(NULL, NULL, EXTRA) }
 
+pass_stmt[stmt_ty]:
+    | 'pass' { _PyAST_Pass(EXTRA) }
+
+break_stmt[stmt_ty]:
+    | 'break' { _PyAST_Break(EXTRA) }
+
+continue_stmt[stmt_ty]:
+    | 'continue' { _PyAST_Continue(EXTRA) }
+
 global_stmt[stmt_ty]: 'global' a[asdl_expr_seq*]=','.NAME+ {
     _PyAST_Global(CHECK(asdl_identifier_seq*, _PyPegen_map_names_to_ids(p, a)), EXTRA) }
 
@@ -1177,13 +1186,31 @@ invalid_type_param:
                 : "cannot use bound with ParamSpec")
         }
 
+invalid_ifexp_orelse_stmt[stmt_ty]:
+    | return_stmt
+    | raise_stmt
+    | pass_stmt
+    | del_stmt
+    | yield_stmt
+    | assert_stmt
+    | break_stmt
+    | continue_stmt
+
+invalid_ifexp_body_stmt[stmt_ty]:
+    | pass_stmt
+    | break_stmt
+    | continue_stmt
+
 invalid_expression:
     # !(NAME STRING) is not matched so we don't show this error with some invalid string prefixes like: kf"dsfsdf"
     # Soft keywords need to also be ignored because they can be parsed as NAME NAME
    | !(NAME STRING | SOFT_KEYWORD) a=disjunction b=expression_without_invalid {
         _PyPegen_check_legacy_stmt(p, a) ? NULL : p->tokens[p->mark-1]->level == 0 ? NULL :
         RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax. Perhaps you forgot a comma?") }
    | a=disjunction 'if' b=disjunction !('else'|':') { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "expected 'else' after 'if' expression") }
+   | a=disjunction 'if' b=disjunction 'else' c=invalid_ifexp_orelse_stmt { RAISE_SYNTAX_ERROR_KNOWN_LOCATION (c, "statement given where 'orelse' expression required")}
+   | a=invalid_ifexp_body_stmt 'if' b=disjunction 'else' c=expression { RAISE_SYNTAX_ERROR_KNOWN_LOCATION (a, "statement given where 'body' expression required")}
+   | a=invalid_ifexp_body_stmt 'if' b=disjunction 'else' c=invalid_ifexp_orelse_stmt { RAISE_SYNTAX_ERROR_KNOWN_LOCATION (a, "statement given where 'body' expression required")}
    | a='lambda' [lambda_params] b=':' &FSTRING_MIDDLE  {
         RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "f-string: lambda expressions are not allowed without parentheses") }
 

Lib/test/test_ast/test_ast.py

@@ -1966,6 +1966,40 @@ def test_ifexp(self):
         for args in (s, l, l), (l, s, l), (l, l, s):
             self.expr(ast.IfExp(*args), "must have Load context")
 
+    def test_ifexp_orelse_stmt(self):
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'orelse' expression required"):
+            ast.parse("x = 1 if 1 else pass")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'orelse' expression required"):
+            ast.parse("x = 1 if 1 else return")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'orelse' expression required"):
+            ast.parse("x = 1 if 1 else raise Exception('a')")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'orelse' expression required"):
+            ast.parse("a = 1; x = 1 if 1 else del a")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'orelse' expression required"):
+            ast.parse("x = 1 if 1 else yield 2")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'orelse' expression required"):
+            ast.parse("x = 1 if 1 else assert False")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'orelse' expression required"):
+            ast.parse("x = 1 if 1 else break")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'orelse' expression required"):
+            ast.parse("x = 1 if 1 else continue")
+
+    def test_ifexp_body_stmt_orelse_expression(self):
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'body' expression required"):
+            ast.parse("x = pass if 1 else 1")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'body' expression required"):
+            ast.parse("x = break if 1 else 1")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'body' expression required"):
+            ast.parse("x = continue if 1 else 1")
+
+    def test_ifexp_body_stmt_orelse_stmt(self):
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'body' expression required"):
+            ast.parse("x = pass if 1 else pass")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'body' expression required"):
+            ast.parse("x = break if 1 else pass")
+        with self.assertRaisesRegex(SyntaxError, "statement given where 'body' expression required"):
+            ast.parse("x = continue if 1 else pass")
+
     def test_dict(self):
         d = ast.Dict([], [ast.Name("x", ast.Load())])
         self.expr(d, "same number of keys as values")

Misc/NEWS.d/next/Core_and_Builtins/2025-02-09-11-30-38.gh-issue-129515.3L3vmo.rst

@@ -0,0 +1,2 @@
+Clarify syntax error messages for conditional expressions if statement
+specified in body and orelse parts.