bpo-37947: Avoid double-decrement in symtable recursion counting (GH-15593)
With `symtable_visit_expr` now correctly adjusting the recursion depth for named expressions, `symtable_handle_namedexpr` should be leaving it alone. Also adds a new check to `PySymtable_BuildObject` that raises `SystemError` if a successful first symbol analysis pass fails to keep the stack depth accounting clean.
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@ -266,6 +266,7 @@ PySymtable_BuildObject(mod_ty mod, PyObject *filename, PyFutureFeatures *future)
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int i;
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PyThreadState *tstate;
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int recursion_limit = Py_GetRecursionLimit();
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int starting_recursion_depth;
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if (st == NULL)
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return NULL;
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@ -284,8 +285,9 @@ PySymtable_BuildObject(mod_ty mod, PyObject *filename, PyFutureFeatures *future)
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return NULL;
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}
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/* Be careful here to prevent overflow. */
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st->recursion_depth = (tstate->recursion_depth < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
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starting_recursion_depth = (tstate->recursion_depth < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
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tstate->recursion_depth * COMPILER_STACK_FRAME_SCALE : tstate->recursion_depth;
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st->recursion_depth = starting_recursion_depth;
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st->recursion_limit = (recursion_limit < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
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recursion_limit * COMPILER_STACK_FRAME_SCALE : recursion_limit;
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@ -329,6 +331,14 @@ PySymtable_BuildObject(mod_ty mod, PyObject *filename, PyFutureFeatures *future)
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PySymtable_Free(st);
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return NULL;
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}
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/* Check that the recursion depth counting balanced correctly */
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if (st->recursion_depth != starting_recursion_depth) {
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PyErr_Format(PyExc_SystemError,
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"symtable analysis recursion depth mismatch (before=%d, after=%d)",
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starting_recursion_depth, st->recursion_depth);
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PySymtable_Free(st);
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return NULL;
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}
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/* Make the second symbol analysis pass */
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if (symtable_analyze(st))
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return st;
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@ -1501,16 +1511,16 @@ symtable_handle_namedexpr(struct symtable *st, expr_ty e)
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PyErr_SyntaxLocationObject(st->st_filename,
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e->lineno,
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e->col_offset);
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VISIT_QUIT(st, 0);
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return 0;
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}
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if (st->st_cur->ste_comprehension) {
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/* Inside a comprehension body, so find the right target scope */
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if (!symtable_extend_namedexpr_scope(st, e->v.NamedExpr.target))
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VISIT_QUIT(st, 0);
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return 0;
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}
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VISIT(st, expr, e->v.NamedExpr.value);
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VISIT(st, expr, e->v.NamedExpr.target);
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VISIT_QUIT(st, 1);
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return 1;
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}
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static int
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