Issue #20731: Properly position in source code files even if they

are opened in text mode. Patch by Serhiy Storchaka.

1 files changed, 12 insertions, 2 deletions

diff --git a/Parser/tokenizer.c b/Parser/tokenizer.c
index 8530723c26..660c0f042b 100644
--- a/Parser/tokenizer.c
+++ b/Parser/tokenizer.c
@@ -498,9 +498,13 @@ fp_setreadl(struct tok_state *tok, const char* enc)
 
     fd = fileno(tok->fp);
     /* Due to buffering the file offset for fd can be different from the file
-     * position of tok->fp. */
+     * position of tok->fp.  If tok->fp was opened in text mode on Windows,
+     * its file position counts CRLF as one char and can't be directly mapped
+     * to the file offset for fd.  Instead we step back one byte and read to
+     * the end of line.*/
     pos = ftell(tok->fp);
-    if (pos == -1 || lseek(fd, (off_t)pos, SEEK_SET) == (off_t)-1) {
+    if (pos == -1 ||
+        lseek(fd, (off_t)(pos > 0 ? pos - 1 : pos), SEEK_SET) == (off_t)-1) {
         PyErr_SetFromErrnoWithFilename(PyExc_OSError, NULL);
         goto cleanup;
     }
@@ -513,6 +517,12 @@ fp_setreadl(struct tok_state *tok, const char* enc)
     Py_XDECREF(tok->decoding_readline);
     readline = _PyObject_GetAttrId(stream, &PyId_readline);
     tok->decoding_readline = readline;
+    if (pos > 0) {
+        if (PyObject_CallObject(readline, NULL) == NULL) {
+            readline = NULL;
+            goto cleanup;
+        }
+    }
 
   cleanup:
     Py_XDECREF(stream);