bpo-45738: Fix computation of error location for invalid continuation characters in the parser (GH-29550) (GH-29552)

(cherry picked from commit 25835c518aa7446f3680b62c1fb43827e0f190d9)

4 files changed, 12 insertions, 11 deletions

diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
index eaa94ea92b..46f27d0444 100644
--- a/Lib/test/test_syntax.py
+++ b/Lib/test/test_syntax.py
@@ -953,7 +953,13 @@ def func2():
     def test_invalid_line_continuation_error_position(self):
         self._check_error(r"a = 3 \ 4",
                           "unexpected character after line continuation character",
-                          lineno=1, offset=(10 if support.use_old_parser() else 9))
+                          lineno=1, offset=8)
+        self._check_error('1,\\#\n2',
+                          "unexpected character after line continuation character",
+                          lineno=1, offset=4)
+        self._check_error('\nfgdfgf\n1,\\#\n2\n',
+                          "unexpected character after line continuation character",
+                          lineno=3, offset=4)
 
     def test_invalid_line_continuation_left_recursive(self):
         # Check bpo-42218: SyntaxErrors following left-recursive rules
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-11-14-00-14-45.bpo-45738.e0cgKd.rst b/Misc/NEWS.d/next/Core and Builtins/2021-11-14-00-14-45.bpo-45738.e0cgKd.rst
new file mode 100644
index 0000000000..b238034323
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-11-14-00-14-45.bpo-45738.e0cgKd.rst
@@ -0,0 +1,2 @@
+Fix computation of error location for invalid continuation characters in the
+parser. Patch by Pablo Galindo.
diff --git a/Parser/pegen/pegen.c b/Parser/pegen/pegen.c
index 98de05c5cd..efcf9ac1eb 100644
--- a/Parser/pegen/pegen.c
+++ b/Parser/pegen/pegen.c
@@ -348,14 +348,7 @@ tokenizer_error(Parser *p)
             msg = "too many levels of indentation";
             break;
         case E_LINECONT: {
-            char* loc = strrchr(p->tok->buf, '\n');
-            const char* last_char = p->tok->cur - 1;
-            if (loc != NULL && loc != last_char) {
-                col_offset = p->tok->cur - loc - 1;
-                p->tok->buf = loc;
-            } else {
-                col_offset = last_char - p->tok->buf - 1;
-            }
+            col_offset = p->tok->cur - p->tok->buf - 1;
             msg = "unexpected character after line continuation character";
             break;
         }
@@ -363,7 +356,8 @@ tokenizer_error(Parser *p)
             msg = "unknown parsing error";
     }
 
-    RAISE_ERROR_KNOWN_LOCATION(p, errtype, p->tok->lineno, col_offset, msg);
+    RAISE_ERROR_KNOWN_LOCATION(p, errtype, p->tok->lineno,
+                               col_offset >= 0 ? col_offset : 0, msg);
     return -1;
 }
 
diff --git a/Parser/tokenizer.c b/Parser/tokenizer.c
index 1a57db97c4..41bfdb853c 100644
--- a/Parser/tokenizer.c
+++ b/Parser/tokenizer.c
@@ -1752,7 +1752,6 @@ tok_get(struct tok_state *tok, const char **p_start, const char **p_end)
         c = tok_nextc(tok);
         if (c != '\n') {
             tok->done = E_LINECONT;
-            tok->cur = tok->inp;
             return ERRORTOKEN;
         }
         c = tok_nextc(tok);