gh-129515: Clarify syntax error messages for conditional expressions

Doc/whatsnew/3.14.rst

@@ -174,6 +174,27 @@ Improved error messages
          ^^^^^^^
      ValueError: too many values to unpack (expected 3, got 4)
 
+* If a statement (:keyword:`!pass`, :keyword:`!del`, :keyword:`!return`, :keyword:`!yield`,
+  :keyword:`!raise`, :keyword:`!break`, :keyword:`!continue`, :keyword:`!assert`)
+  is passed to the :ref:`if_expr`, then the error message highlights where
+  the :token:`~python-grammar:expression` is required.
+
+  .. code-block:: pycon
+
+     >>> x = 1 if True else pass
+     Traceback (most recent call last):
+       File "<string>", line 1
+         x = 1 if True else pass
+                            ^^^^
+     SyntaxError: statement given where 'orelse' expression required
+
+     >>> x = continue if True else break
+     Traceback (most recent call last):
+       File "<string>", line 1
+         x = continue if True else break
+             ^^^^^^^^
+     SyntaxError: statement given where 'body' expression required
+
 
 .. _whatsnew314-pep741:
 

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) }
 
@@ -1184,6 +1193,11 @@ invalid_expression:
         _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[stmt_ty]=(
+        return_stmt | raise_stmt | pass_stmt | del_stmt | yield_stmt | assert_stmt | break_stmt | continue_stmt) {
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION (c, "statement given where 'orelse' expression required") }
+   | a[stmt_ty]=(pass_stmt|break_stmt|continue_stmt) 'if' b=disjunction 'else' c=simple_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 +1966,42 @@ 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):
+        msg = "statement given where 'orelse' expression required"
+        for stmt in [
+            "x = 1 if 1 else pass",
+            "x = 1 if 1 else return",
+            "x = 1 if 1 else raise Exception('a')",
+            "x = 1 if 1 else del a",
+            "x = 1 if 1 else yield 2",
+            "x = 1 if 1 else assert False",
+            "x = 1 if 1 else break",
+            "x = 1 if 1 else continue"
+        ]:
+            with self.subTest(stmt), self.assertRaisesRegex(SyntaxError, msg):
+                ast.parse(stmt)
+
+    def test_ifexp_body_stmt_orelse_expression(self):
+        msg = "statement given where 'body' expression required"
+        for stmt in [
+            "x = pass if 1 else 1",
+            "x = break if 1 else 1",
+            "x = continue if 1 else 1"
+        ]:
+            with self.subTest(stmt), self.assertRaisesRegex(SyntaxError, msg):
+                ast.parse(stmt)
+
+    def test_ifexp_body_stmt_orelse_stmt(self):
+        msg = "statement given where 'body' expression required"
+        for stmt in [
+            "x = pass if 1 else pass",
+            "x = break if 1 else pass",
+            "x = continue if 1 else pass",
+            "x = continue if 1 else import ast"
+        ]:
+            with self.subTest(stmt), self.assertRaisesRegex(SyntaxError, msg):
+                ast.parse(stmt)
+
     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.