bpo-1514420: Do not attempt to open files with names in <>s when formatting an exception (GH-28143)

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Łukasz Langa <[email protected]>

Author: 3 people

Misc/NEWS.d/next/Core and Builtins/2021-09-03-16-18-10.bpo-1514420.2Lumpj.rst

@@ -0,0 +1 @@
+Interpreter no longer attempts to open files with names in angle brackets (like "<string>" or "<stdin>") when formatting an exception.

Python/traceback.c

@@ -396,6 +396,15 @@ _Py_DisplaySourceLine(PyObject *f, PyObject *filename, int lineno, int indent, i
     if (filename == NULL)
         return 0;
 
+    /* Do not attempt to open things like <string> or <stdin> */
+    assert(PyUnicode_Check(filename));
+    if (PyUnicode_READ_CHAR(filename, 0) == '<') {
+        Py_ssize_t len = PyUnicode_GET_LENGTH(filename);
+        if (len > 0 && PyUnicode_READ_CHAR(filename, len - 1) == '>') {
+            return 0;
+        }
+    }
+
     io = PyImport_ImportModuleNoBlock("io");
     if (io == NULL)
         return -1;