bpo-15248: Emit a compiler warning when missed a comma before tuple or list. (GH-11757)

1 files changed, 87 insertions, 0 deletions

diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index 74590eb..2ee38f0 100644
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -1263,6 +1263,93 @@ class GrammarTests(unittest.TestCase):
             compile('x is True', '<testcase>', 'exec')
             compile('x is ...', '<testcase>', 'exec')
 
+    def test_warn_missed_comma(self):
+        def check(test):
+            with self.assertWarnsRegex(SyntaxWarning, msg):
+                compile(test, '<testcase>', 'exec')
+            with warnings.catch_warnings():
+                warnings.filterwarnings('error', category=SyntaxWarning)
+                with self.assertRaisesRegex(SyntaxError, msg):
+                    compile(test, '<testcase>', 'exec')
+
+        msg=r'is not callable; perhaps you missed a comma\?'
+        check('[(1, 2) (3, 4)]')
+        check('[(x, y) (3, 4)]')
+        check('[[1, 2] (3, 4)]')
+        check('[{1, 2} (3, 4)]')
+        check('[{1: 2} (3, 4)]')
+        check('[[i for i in range(5)] (3, 4)]')
+        check('[{i for i in range(5)} (3, 4)]')
+        check('[(i for i in range(5)) (3, 4)]')
+        check('[{i: i for i in range(5)} (3, 4)]')
+        check('[f"{x}" (3, 4)]')
+        check('[f"x={x}" (3, 4)]')
+        check('["abc" (3, 4)]')
+        check('[b"abc" (3, 4)]')
+        check('[123 (3, 4)]')
+        check('[12.3 (3, 4)]')
+        check('[12.3j (3, 4)]')
+        check('[None (3, 4)]')
+        check('[True (3, 4)]')
+        check('[... (3, 4)]')
+
+        msg=r'is not subscriptable; perhaps you missed a comma\?'
+        check('[{1, 2} [i, j]]')
+        check('[{i for i in range(5)} [i, j]]')
+        check('[(i for i in range(5)) [i, j]]')
+        check('[(lambda x, y: x) [i, j]]')
+        check('[123 [i, j]]')
+        check('[12.3 [i, j]]')
+        check('[12.3j [i, j]]')
+        check('[None [i, j]]')
+        check('[True [i, j]]')
+        check('[... [i, j]]')
+
+        msg=r'indices must be integers or slices, not tuple; perhaps you missed a comma\?'
+        check('[(1, 2) [i, j]]')
+        check('[(x, y) [i, j]]')
+        check('[[1, 2] [i, j]]')
+        check('[[i for i in range(5)] [i, j]]')
+        check('[f"{x}" [i, j]]')
+        check('[f"x={x}" [i, j]]')
+        check('["abc" [i, j]]')
+        check('[b"abc" [i, j]]')
+
+        msg=r'indices must be integers or slices, not tuple;'
+        check('[[1, 2] [3, 4]]')
+        msg=r'indices must be integers or slices, not list;'
+        check('[[1, 2] [[3, 4]]]')
+        check('[[1, 2] [[i for i in range(5)]]]')
+        msg=r'indices must be integers or slices, not set;'
+        check('[[1, 2] [{3, 4}]]')
+        check('[[1, 2] [{i for i in range(5)}]]')
+        msg=r'indices must be integers or slices, not dict;'
+        check('[[1, 2] [{3: 4}]]')
+        check('[[1, 2] [{i: i for i in range(5)}]]')
+        msg=r'indices must be integers or slices, not generator;'
+        check('[[1, 2] [(i for i in range(5))]]')
+        msg=r'indices must be integers or slices, not function;'
+        check('[[1, 2] [(lambda x, y: x)]]')
+        msg=r'indices must be integers or slices, not str;'
+        check('[[1, 2] [f"{x}"]]')
+        check('[[1, 2] [f"x={x}"]]')
+        check('[[1, 2] ["abc"]]')
+        msg=r'indices must be integers or slices, not'
+        check('[[1, 2] [b"abc"]]')
+        check('[[1, 2] [12.3]]')
+        check('[[1, 2] [12.3j]]')
+        check('[[1, 2] [None]]')
+        check('[[1, 2] [...]]')
+
+        with warnings.catch_warnings():
+            warnings.filterwarnings('error', category=SyntaxWarning)
+            compile('[(lambda x, y: x) (3, 4)]', '<testcase>', 'exec')
+            compile('[[1, 2] [i]]', '<testcase>', 'exec')
+            compile('[[1, 2] [0]]', '<testcase>', 'exec')
+            compile('[[1, 2] [True]]', '<testcase>', 'exec')
+            compile('[[1, 2] [1:2]]', '<testcase>', 'exec')
+            compile('[{(1, 2): 3} [i, j]]', '<testcase>', 'exec')
+
     def test_binary_mask_ops(self):
         x = 1 & 1
         x = 1 ^ 1