Improve SyntaxError suggestions for common operator typos

Author: Aniketsy

Grammar/python.gram

@@ -812,7 +812,7 @@ invalid_diamond_op:
     }
 eq_bitwise_or[CmpopExprPair*]: '==' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Eq, a) }
 invalid_eqeqeq:
-    | a='==' b='=' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant '==' instead of '==='?") }
+    | a='==' b='=' { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "invalid syntax.  Maybe you meant 'is' instead of '==='?") }
 noteq_bitwise_or[CmpopExprPair*]:
     | (tok='!=' { _PyPegen_check_barry_as_flufl(p, tok) ? NULL : tok}) a=bitwise_or {_PyPegen_cmpop_expr_pair(p, NotEq, a) }
 lte_bitwise_or[CmpopExprPair*]: '<=' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, LtE, a) }

Lib/test/test_syntax.py

@@ -3507,12 +3507,12 @@ def test_ifexp_body_stmt_else_stmt(self):
 
     def test_diamond_operator(self):
         self._check_error(
-            "1 < > 2",
-            "Maybe you meant '!=' instead of '<>'?",
+            "1<>2",
+            r'Are you trying to overthrow the SC\?  Use operator "!="!',
             lineno=1,
             end_lineno=1,
-            offset=3,
-            end_offset=6,
+            offset=2,
+            end_offset=4,
         )
 
     def test_diamond_operator_barry_as_flufl(self):
@@ -3528,7 +3528,7 @@ def test_diamond_operator_barry_as_flufl(self):
     def test_triple_equal(self):
         self._check_error(
             "a === b",
-            "Maybe you meant '==' instead of '==='?",
+            "Maybe you meant 'is' instead of '==='?",
             lineno=1,
             end_lineno=1,
             offset=3,

Parser/action_helpers.c

@@ -931,6 +931,10 @@ _PyPegen_check_barry_as_flufl(Parser *p, Token* t) {
         return -1;
     }
     if (!(p->flags & PyPARSE_BARRY_AS_BDFL)) {
+        if (strcmp(tok_str, "<>") == 0) {
+            RAISE_SYNTAX_ERROR("Are you trying to overthrow the SC?  Use operator \"!=\"!");
+            return -1;
+        }
         return strcmp(tok_str, "!=");
     }
     return 0;