bpo-45811: Improve error message when source code contains invisible control characters

Author: pablogsal

Lib/test/test_syntax.py

@@ -1528,6 +1528,9 @@ def test_error_parenthesis(self):
         for paren in ")]}":
             self._check_error(paren + "1 + 2", f"unmatched '\\{paren}'")
 
+    def test_invisible_characters(self):
+        self._check_error('print\x17("Hello")', "invalid non-printable character")
+
     def test_match_call_does_not_raise_syntax_error(self):
         code = """
 def match(x):

Misc/NEWS.d/next/Core and Builtins/2021-11-20-02-25-06.bpo-45811.B-1Gsr.rst

@@ -0,0 +1,2 @@
+Improve the tokenizer errors when encountering invisible control characters
+in the parser. Patch by Pablo Galindo

Parser/tokenizer.c

@@ -2045,6 +2045,12 @@ tok_get(struct tok_state *tok, const char **p_start, const char **p_end)
         break;
     }
 
+    if (!Py_UNICODE_ISPRINTABLE(c)) {
+        char hex[9];
+        (void)PyOS_snprintf(hex, sizeof(hex), "%04X", c);
+        return syntaxerror(tok, "invalid non-printable character U+%s", hex);
+    }
+
     /* Punctuation character */
     *p_start = tok->start;
     *p_end = tok->cur;