bpo-43121: Fix incorrect SyntaxError message for missing comma (GH-24436)

Grammar/python.gram

@@ -694,7 +694,7 @@ invalid_primary:
 invalid_comprehension:
     | ('[' | '(' | '{') a=starred_expression for_if_clauses {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "iterable unpacking cannot be used in comprehension") }
-    | ('[' | '{') a=star_named_expression ',' [star_named_expressions] {
+    | ('[' | '{') a=star_named_expression ',' [star_named_expressions] for_if_clauses {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "did you forget parentheses around the comprehension target?") }
 invalid_dict_comprehension:
     | '{' a='**' bitwise_or for_if_clauses '}' {

Lib/test/test_syntax.py

@@ -246,9 +246,25 @@ SyntaxError: did you forget parentheses around the comprehension target?
 Traceback (most recent call last):
 SyntaxError: did you forget parentheses around the comprehension target?
 
->>> {x,y: None for x,y in range(100)}
+# Missing commas in literals collections should not
+# produce special error messages regarding missing
+# parentheses
+
+>>> [1, 2 3]
 Traceback (most recent call last):
-SyntaxError: did you forget parentheses around the comprehension target?
+SyntaxError: invalid syntax
+
+>>> {1, 2 3}
+Traceback (most recent call last):
+SyntaxError: invalid syntax
+
+>>> {1:2, 2:5 3:12}
+Traceback (most recent call last):
+SyntaxError: invalid syntax
+
+>>> (1, 2 3)
+Traceback (most recent call last):
+SyntaxError: invalid syntax
 
 From compiler_complex_args():
 

Misc/NEWS.d/next/Core and Builtins/2021-02-03-22-33-05.bpo-43121.jqcViq.rst

@@ -0,0 +1,2 @@
+Fixed an incorrect :exc:`SyntaxError` message for missing comma in literals.
+Patch by Pablo Galindo.

Parser/parser.c

@@ -15217,7 +15217,7 @@ invalid_primary_rule(Parser *p)
 
 // invalid_comprehension:
 //     | ('[' | '(' | '{') starred_expression for_if_clauses
-//     | ('[' | '{') star_named_expression ',' star_named_expressions?
+//     | ('[' | '{') star_named_expression ',' star_named_expressions? for_if_clauses
 static void *
 invalid_comprehension_rule(Parser *p)
 {
@@ -15258,17 +15258,18 @@ invalid_comprehension_rule(Parser *p)
         D(fprintf(stderr, "%*c%s invalid_comprehension[%d-%d]: %s failed!\n", p->level, ' ',
                   p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "('[' | '(' | '{') starred_expression for_if_clauses"));
     }
-    { // ('[' | '{') star_named_expression ',' star_named_expressions?
+    { // ('[' | '{') star_named_expression ',' star_named_expressions? for_if_clauses
         if (p->error_indicator) {
             D(p->level--);
             return NULL;
         }
-        D(fprintf(stderr, "%*c> invalid_comprehension[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "('[' | '{') star_named_expression ',' star_named_expressions?"));
+        D(fprintf(stderr, "%*c> invalid_comprehension[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "('[' | '{') star_named_expression ',' star_named_expressions? for_if_clauses"));
         Token * _literal;
         void *_opt_var;
         UNUSED(_opt_var); // Silence compiler warnings
         void *_tmp_132_var;
         expr_ty a;
+        asdl_comprehension_seq* for_if_clauses_var;
         if (
             (_tmp_132_var = _tmp_132_rule(p))  // '[' | '{'
             &&
@@ -15277,9 +15278,11 @@ invalid_comprehension_rule(Parser *p)
             (_literal = _PyPegen_expect_token(p, 12))  // token=','
             &&
             (_opt_var = star_named_expressions_rule(p), 1)  // star_named_expressions?
+            &&
+            (for_if_clauses_var = for_if_clauses_rule(p))  // for_if_clauses
         )
         {
-            D(fprintf(stderr, "%*c+ invalid_comprehension[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "('[' | '{') star_named_expression ',' star_named_expressions?"));
+            D(fprintf(stderr, "%*c+ invalid_comprehension[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "('[' | '{') star_named_expression ',' star_named_expressions? for_if_clauses"));
             _res = RAISE_SYNTAX_ERROR_KNOWN_LOCATION ( a , "did you forget parentheses around the comprehension target?" );
             if (_res == NULL && PyErr_Occurred()) {
                 p->error_indicator = 1;
@@ -15290,7 +15293,7 @@ invalid_comprehension_rule(Parser *p)
         }
         p->mark = _mark;
         D(fprintf(stderr, "%*c%s invalid_comprehension[%d-%d]: %s failed!\n", p->level, ' ',
-                  p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "('[' | '{') star_named_expression ',' star_named_expressions?"));
+                  p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "('[' | '{') star_named_expression ',' star_named_expressions? for_if_clauses"));
     }
     _res = NULL;
   done: